Fe3O4 @SiO2 -hexamethyldisilazane amphiphilic magnetic emulsifier for viscosity-reduction of heavy oils via aquathermolysis reaction

Fe3O4 @SiO2 -hexamethyldisilazane amphiphilic magnetic emulsifier for viscosity-reduction of heavy oils via aquathermolysis reaction | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Fe 3 O 4 @SiO 2 -hexamethyldisilazane amphiphilic magnetic emulsifier for viscosity-reduction of heavy oils via aquathermolysis reaction Yaoyao Feng, Xiaoxun Li This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8769823/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 14 You are reading this latest preprint version Abstract Heavy oil accounts for a large share of global proven oil reserves and is thus a key energy resource. Yet its high viscosity and freezing point require complex, specialized processing. While chemical, microbial, and thermal recovery methods exist, a simple, controllable, and highly effective viscosity reduction method is still needed. Here, novel Fe₃O₄@SiO₂ nanoparticles capped with hexamethyldisilazane (HMDS) were synthesized as magnetic emulsifiers to reduce the viscosity of heavy oil. The as-synthesized Fe₃O₄@SiO₂-HMDS nanoparticles exhibit an average size of approximately 100 nm, along with good dispersion in oil and magnetic responsiveness. As emulsifiers, these nanoparticles promote the aquathermolysis reaction of extra-heavy crude oil at relatively low temperatures. Specifically, in our experiments, the amphiphilic emulsifier ME-8, with an SiO₂/HMDS molar ratio of 8:1, effectively reduced the apparent viscosity of three heavy oil samples (with initial viscosities of 27,500 cP, 58,000 cP, and 85,400 cP) by 67.27%, 68.96%, and 56.67%, respectively. These results were achieved under optimal conditions: an emulsifier mass fraction of 0.5%, a reaction temperature of 150°C, and a reaction time of 24 hours. This emulsifier-based method demonstrates promising potential for the exploitation of heavy crude oil. Heavy oil Emulsifier Fe3O4@SiO2-HMDS Viscosity-reduction Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1 Introduction Heavy oil, which constitutes a large portion of the world's proven oil reserves, serves as a major source of hydrocarbon energy. However, its high viscosity and high freezing point pose significant challenges to extraction and transportation (Santos et al. 2014 ; Li et al. 2021 ; Xiong et al. 2024 ; Xue et al. 2022 ; Nguyen et al. 2013; Karimov et al. 2024). Currently, most of the confirmed large deposits of bitumen and heavy oil are located in Venezuela, Canada, and the United States. In China, the proven and controlled heavy oil reserves amount to approximately 1.6 billion tons, accounting for about 30% of the world’s total heavy oil reserves. Compared with conventional crude oil, heavy oil contains a higher proportion of long-chain and cyclic hydrocarbons (Zhao et al. 2020 ; Ashrafizadeh et al. 2010; Hannisdal et al. 2006 ). These components contribute to its high viscosity, high density, and poor flowability, making extraction particularly difficult (Liu et al. 2024 ; Pratama et al. 2022; He et al. 2015 ; Yao et al. 2023 ). Therefore, reducing viscosity and enhancing mobility are crucial for the effective exploitation of heavy oil resources and there is an urgent need to develop novel and efficient viscosity-reduction methods to improve heavy oil production . Over the years, numerous techniques including thermal (Khelkhal et al. 2022 ; Bueno et al. 2022; Sun et al. 2024 ), chemical (Chen et al. 2010 ; Ding et al. 2020 ; Ahmadi et al. 2024; Liu et al. 2022 ; Zhang et al. 2025 ; Zhang et al. 2024 ), microbial recovery (Liurdes et al. 2022 ; Wu et al. 2022 ; Nadarajah et al. 2002 ), Nanoparticals (Al-Janabi et al. 2023 ; Sun et al. 2013 ; Sajid et al. 2023 ) other methods (Binks et al. 2007; Chen et al. 2023 ; Lu et al. 2020 ; Li et al. 2025 ) have been developed for heavy oil exploitation. For example, chemically induced oil-in-water (O/W) emulsions emerged as a potential means to reduce the viscosity of produced fluids (Al-Sabagh et al. 2011 ; Liang et al. 2015 ; Ali et al. 2015 ; Peng et al. 2012 ; Zhu et al. 2015 ). When low molecular-weight surfactants and water are injected into the flow system, the resulting O/W emulsion is particularly significant for the low-cost extraction of heavy oil due to its substantial viscosity reduction effect. However, the application of O/W emulsions in promoting the aquathermolysis of heavy oil remains limited, primarily due to the difficulty in breaking these emulsions. Traditionally, fine solids with appropriate surface wettability, such as montmorillonite, sandstone, alumina, clay, Ca(OH)₂, and silica, can stabilize emulsions and help them retain desired properties in produced fluids (Yan et al. 2001 ; Melle et al. 2005 ; Jiang et al. 2013 ; Binks et al. 2006). This stability is especially important in unconventional petroleum production. Therefore, the study of interfacial properties in particle-stabilized petroleum emulsions deserves special attention. For instance, Ramsden and Pickering prepared emulsions with long-term stability and found that particles with a solid–liquid contact angle close to 90° are most effective in stabilizing O/W emulsions (Liang et al. 2015 ).[35] Jung et al. suggested that silica nanoparticles are among the most promising nanomaterials for oil recovery because their oil compatibility can be greatly enhanced through surface modification with silane (Jung et al. 2012 ). Although such emulsions can improve heavy oil production efficiency, breaking these highly stable emulsions remains a major challenge during crude oil refining. To address this bottleneck, researchers have developed magnetite nanoparticles as demulsifiers that can be activated by an external magnetic field. These magnetic sub-micron particles can be easily recycled via magnetic separation and solvent washing, while the external field enhances the coalescence of magnetically tagged water droplets within the emulsion. Here, our study focuses on the application of magnetic nanoparticles for stabilizing emulsions and reducing the viscosity of heavy oil. We grafted HMDS (hexamethyldisilazane), a hydrophobic modifying agent, onto the surface of magnetic Fe₃O₄@SiO₂ nanoparticles to synthesize a novel magnetic emulsifier, Fe₃O₄@SiO₂-HMDS. This emulsifier demonstrated remarkable performance in reducing the viscosity of three types of extra-heavy oil during an aquathermolysis process simulated using a rolling apparatus to mimic flow conditions. The reduction in viscosity is attributed to the ability of the magnetic nanoparticles to promote the formation of stable oil-in-water (O/W) Pickering emulsions. The amphiphilic emulsifier ME-8, with an optimal SiO₂/HMDS molar ratio of 8:1, significantly reduced the apparent viscosity of heavy oil samples (initial viscosities: 27,500 cP, 58,000 cP, and 85,400 cP) by 67.27%, 68.96%, and 56.67%, respectively. These results were achieved under the following optimized conditions: emulsifier mass fraction of 0.5%, reaction temperature of 150°C, and reaction time of 24 h. In addition to its high efficiency in viscosity reduction, the Fe₃O₄@SiO₂-HMDS emulsifier can be easily recovered via magnetic separation due to its superparamagnetic properties, enabling recyclability and reducing operational costs. The combination of significant viscosity reduction and straightforward recovery highlights the potential of this magnetic emulsifier in sustainable heavy oil exploitation. 2 Material and methods 2.1 Materials Ferric chloride hexahydrate (FeCl 3 ·6H 2 O, analytical grade reagent (AR)), ethylene glycol ((CH 2 OH) 2 , AR), sodium citrate (Na 3 C 6 H 5 O 7 ·2H 2 O, AR), sodium acetate (C 2 H 9 NaO 5 , AR), and ammonium chloride (NH 4 Cl, AR) were purchased from Tianjin Kemiou Chemical Reagent Technology Company Ltd (Tianjin, China). Polyethylene glycol (HO(CH 2 CH 2 O) n H, molecular weight 4000, AR) was commercially obtained from Tianjin Fuyu Fine Chemical Company Ltd (Tianjin, China). Sodium silicate (Na 2 SiO 3 ·9H 2 O) was provided by Kaifeng Dongda Chemical Company Ltd (Kaifeng, China). 1,1,1,3,3,3-hexamethyldisilazane (C 6 H 19 NSi 2 , AR) was purchased from Hangzhou Guibao Chemical Company Ltd (Hangzhou, China). Industrial alcohol was provided by Tianjin Chengtongtai Chemical Company Ltd (Tianjin, China). The three kinds of heavy oil samples (viscosity at 50 o C: 27500 cP, 58000cP and 85400cP), coded as oil samples A, B and C, respectively, were produced at Shengli Oilfield (Dongying, China). 2.2 Preparation of Fe 3 O 4 @SiO 2 -HMDS magnetic emulsifier Figure 1 a schematically illustrates the preparation route of the Fe₃O₄@SiO₂-HMDS magnetic emulsifier. Briefly, core–shell structured Fe₃O₄ spheres were synthesized via a coprecipitation method, followed by coating with a SiO₂ layer using a modified Stöber method. The as-prepared Fe₃O₄@SiO₂ nanoparticles were retained in the reactor, and HMDS was gradually introduced to form a suspension. This suspension was then heated to 70°C and maintained at this temperature for 2 h, after which it was filtered. The filtered cake was repeatedly washed with deionized water until no Cl⁻ could be detected using aqueous silver nitrate. Finally, the product was vacuum-dried overnight to obtain the target Fe₃O₄@SiO₂-HMDS composite nanoparticles. By varying the molar ratio of silicon dioxide to HMDS as 4:1, 6:1, 8:1, 10:1, and 12:1, while keeping other parameters constant—a series of corresponding magnetic emulsifiers (abbreviated as ME-4, ME-6, ME-8, ME-10, and ME-12) were obtained. This approach allows for a balance between hydrophilic silanol groups and hydrophobic trimethylsilyl groups. As a result, the emulsifier exhibits improved dispersion at the oil–water interface and enhanced emulsifying capability. 2.3 Evaluation of viscosity-reducing performance of Fe 3 O 4 @SiO 2 -HMDS magnetic emulsifiers for the aquathermolysis reaction of heavy oils The viscosity reduction performance of the magnetic emulsifiers, prepared for the hydrothermal cracking reaction of three heavy oils, was evaluated using an LHG-3 autoclave reactor (Fig. 1 b). Briefly, 100 g of heavy oil, 50 g of deionized water, and 0.5 g of the as-synthesized magnetic emulsifier were placed into the reactor. The mixture was heated to 150°C and maintained at that temperature for 24 hours to complete the aquathermolysis reaction. After the reaction, the system was allowed to cool naturally to room temperature.The viscosity of the oil samples before and after aquathermolysis was measured at 50°C using a Brookfield DV-III programmable viscometer. The viscosity reduction ratio was calculated as follows: Δη = (η₀ − η) / η₀ × 100% (1) where Δη (%) represents the viscosity reduction ratio, η₀ (cP) is the viscosity of the original heavy oil, and η (cP) is the viscosity of the heavy oil after the emulsion aquathermolysis reaction. In addition, column chromatographic separation was performed in accordance with the Chinese petroleum industry standard SY/T 5119 − 2008 to isolate four components, saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltenes (collectively referred to as SARA), from the oil samples. 2.4 Characterization of magnetic emulsifier As-prepared Fe 3 O 4 @SiO 2 -HMDS magnetic emulsifiers were characterized by transmission electron microscopy (TEM; JEM 2010; JEOL, Japan), X-ray diffraction (XRD; Bruker XRD D8 Advance diffractometer, Bruker Spectrum Instrument Company, Germany), and Fourier transform infrared spectroscopy (FTIR; AVATAR-360, Nigaoli Instrument Company, USA; wavenumber range 400–4000 cm − 1 ). 3 Results and discussion 3.1 Characterization of as-prepared Fe 3 O 4 @SiO 2 -HMDS magnetic emulsifier Figure 2 presents TEM images of the as-prepared Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂-HMDS composite nanoparticles. As shown in Fig. 2 a and 2 b, the Fe₃O₄@SiO₂ nanoparticles exhibit a spherical morphology with diameters ranging from 90 to 100 nm; however, a significant degree of aggregation is observed among these particles. This aggregation can be attributed to the presence of active surface silanol (–SiOH) groups, which promote interparticle hydrogen bonding and van der Waals interactions, leading to the assembly of individual nanoparticles into larger clusters. In contrast, after modification with HMDS, the Fe₃O₄@SiO₂-HMDS nanoparticles maintain their spherical shape but show a slight increase in diameter and a remarkable improvement in dispersibility, as illustrated in Fig. 2 c and 2 d. The grafting of hydrophobic trimethylsilyl groups via HMDS replaces the hydrophilic surface hydroxyl groups, thereby introducing steric hindrance that reduces particle–particle adhesion and agglomeration tendencies. As a result, the modified nanoparticles are better stabilized in organic media, and their crystal growth proceeds in a more controlled manner, yielding well-dispersed and structurally well-defined nanoparticles suitable for application in Pickering emulsion systems and interfacial catalysis . Figure 3 presents the XRD patterns of the ME-4, ME-6, ME-8, ME-10, and ME-12 magnetic nanoparticles. The weak and broad diffraction features observed in the 2θ range of 20°–30° correspond to amorphous silica (SiO₂), which is consistent with the typical characteristics of a non-crystalline SiO₂ coating. The intensity of this amorphous hump gradually decreases from ME-4 to ME-12, and it is weakest in the ME-0 sample (unmodified Fe₃O₄@SiO₂). This trend suggests that as the HMDS-to-SiO₂ ratio increases, the surface modification influences the long-range ordering of the silica shell, leading to a progressively less distinct amorphous signal. Simultaneously, the distinct diffraction peaks observed at 2θ values of 30.12°, 37.12°, 43.12°, 53.40°, 57.02°, and 62.56° are readily indexed to the (220), (311), (400), (422), (511), and (440) crystal planes, respectively, of magnetite (Fe₃O₄) with an inverse cubic spinel structure (JCPDS card no. 65-3107). This confirms that the core magnetic phase remains intact throughout the synthesis and modification process. When compared to the unmodified Fe₃O₄@SiO₂ (ME-0), the Fe₃O₄@SiO₂-HMDS samples exhibit a noticeable weakening in the intensity of these characteristic Fe₃O₄ peaks. This attenuation indicates that the surface capping by HMDS introduces a certain degree of structural distortion or reduces the coherent scattering domain size at the crystal surface, leading to a measurable reduction in the apparent crystallinity of the magnetite phase. However, the fact that the peak positions remain unchanged confirms that the underlying crystal structure of the ferrimagnetic Fe₃O₄ core is not altered by the hydrophobic surface modification, preserving the essential magnetic properties of the nanoparticles . Figure 4 presents the Fourier Transform Infrared Spectroscopy (FTIR) spectra of ME-8 and the unmodified reference sample ME-0 (Fe₃O₄@SiO₂). The spectrum of ME-0 exhibits characteristic absorption bands at 1096 cm⁻¹ and 797 cm⁻¹, which are attributed to the anti-symmetric stretching vibration and bending vibration of the Si–O–Si framework, respectively, confirming the formation of a silica (SiO₂) coating on the magnetic nanoparticles. Additionally, broad absorption bands observed at 3427 cm⁻¹ and 1634 cm⁻¹ correspond to the O–H stretching vibration and H–O–H bending vibration of adsorbed water molecules, indicating the presence of surface silanol (Si–OH) groups and physisorbed water in the as-synthesized composites. The presence of these hydroxyl groups is consistent with the hydrophilic nature of the unmodified silica surface, which tends to form hydrogen-bonded silanol nests that strongly adsorb water. In contrast, the spectrum of ME-8 shows additional peaks at 2966 cm⁻¹, 1254 cm⁻¹, and 845 cm⁻¹, which are assigned to the symmetric and asymmetric stretching vibrations of C–H bonds in –CH₃ groups and the stretching vibration of Si–C bonds, respectively. These features indicate the successful grafting of hexamethyldisilazane (HMDS) onto the silica surface, where the hydrophobic trimethylsilyl groups (–Si(CH₃)₃) have replaced the original hydrophilic silanol groups via covalent bonding. The reduction in intensity of the O–H stretching band at 3427 cm⁻¹ further supports the effective surface modification, confirming that HMDS capping reduces surface hydrophilicity and enhances the compatibility of the nanoparticles with organic media such as heavy oil. This covalent functionalization not only improves the dispersion of nanoparticles at the oil-water interface but also contributes to the amphiphilic character of the ME-8 emulsifier, which is essential for stabilizing Pickering emulsions and facilitating the aquathermolysis process during viscosity reduction. To further evaluate the hydrophobic characteristics of the magnetic emulsifiers, emulsions of ME-4, ME-6, ME-8, ME-10, and ME-12 were prepared using a rolling machine at room temperature, with the magnetic emulsifier concentration fixed at 4 × 10⁻³ g/L. The state of the resulting emulsions was observed using a digital camera. Concurrently, the water contact angles on the surfaces of compressed magnetic composite disks were measured using a solid–liquid interface analyzer (DM300, Kyowa Interface Science Co., Ltd., Japan) to quantitatively assess their wettability. As shown in Fig. 5a , ME-4 and ME-6 powders, exhibiting strong hydrophobicity, float entirely on the water surface, whereas ME-10 and ME-12 powders are completely dispersed in the aqueous phase. ME-8 presents an intermediate behavior: a portion of the powder floats while the emulsion appears somewhat turbid. Correspondingly, the water contact angles measured for ME-4, ME-6, ME-8, ME-10, and ME-12 are approximately 160°, 145°, 80°, 0°, and 0°, respectively (Fig. 5b). These results clearly indicate that as the HMDS dosage increases, the hydrophobicity of the Fe₃O₄@SiO₂ nanoparticles is significantly enhanced due to the progressive replacement of hydrophilic silanol groups (─SiOH) on the silica surface with hydrophobic trimethylsilyl groups (─Si(CH₃)₃) introduced by HMDS. The contact angle, as described by the Young-Laplace equation, reflects the balance of interfacial tensions at the solid–liquid–gas boundary, and its variation here directly correlates with the changing surface chemistry of the nanoparticles. It can therefore be inferred that surface modification with HMDS effectively tunes the wettability of the nanoparticles from hydrophilic to highly hydrophobic. As the SiO₂/HMDS molar ratio decreases from ME-12 to ME-4, the increasing coverage of trimethylsilyl groups reduces the surface free energy and enhances the affinity toward oil phases. ME-8, with its balanced composition, possesses both residual hydrophilic silanol groups and grafted hydrophobic trimethylsilyl groups, rendering it amphiphilic. This amphiphilic character allows ME-8 to act as an effective surfactant, facilitating the stabilization of oil, water interfaces, crucial for forming and stabilizing Pickering emulsions in heavy oil aquathermolysis processes . Figure 5. (a) The optical photos of the emulsifiers, a: ME-4, b: ME-6, c: ME-8, d: ME-10 and :e: ME-12 (b)Water contact angle measurements of compressed magnetic composite disks corresponding to the emulsifiers, a:160 o , b: 145 o , c: 80 o , d: 0 o and e: 0 o . Figure 6 presents the magnetic properties of the Fe₃O₄@SiO₂-HMDS microspheres measured at 300 K using a vibrating sample magnetometer (VSM). The saturation magnetization (Mₛ) value was determined to be 54.3 emu/g, which is lower than that of uncoated magnetite (typically ~ 90 emu/g for bulk Fe₃O₄) due to the diamagnetic contribution of the SiO₂ shell and the surface grafting of HMDS, both of which reduce the overall magnetic moment per unit mass. This high Mₛ ensures strong magnetic responsiveness, critical for magnetic separation and guidance. To demonstrate this, Fe₃O₄@SiO₂-HMDS microspheres were dispersed in diesel with and without an external magnetic field. After vigorous shaking, they formed a stable brown suspension, confirming good dispersibility in the organic medium, enabled by hydrophobic HMDS surface modification. When a magnet was applied, the microspheres rapidly aggregated toward the field source, cleanly separating from the diesel. This fast response reflects strong magnetic dipole interactions, typical of ferrimagnetic Fe₃O₄ with single- or multi-domain cores. The combination of field-free dispersibility and field-triggered aggregation demonstrates excellent magnetic controllability, key for demulsification and enhanced oil recovery: the particles uniformly disperse in heavy oil emulsions to promote interfacial activity, then are efficiently recovered via magnetic separation after reducing viscosity, improving process efficiency and lowering operational costs. 3.2 The effect of Fe 3 O 4 @SiO 2 -HMDS magnetic emulsifiers on the aquathermolysis reaction of heavy oils Figure 7 illustrates the proposed mechanism of the viscosity-reduction process utilizing the Fe₃O₄@SiO₂-HMDS magnetic emulsifier. In this system, the SiO₂ shell (bearing silanol groups, –SiOH) serves as the hydrophilic moiety, while the long-chain HMDS grafted onto the surface acts as the hydrophobic moiety. When water and the emulsifier are introduced into the crude oil, the amphiphilic nature of the nanoparticles promotes the formation of oil-in-water (O/W) or water-in-oil (W/O) Pickering emulsions, depending on the three-phase contact angle, through vigorous shearing or rolling. The nanoparticles spontaneously migrate to and adsorb strongly at the oil–water interface, significantly lowering the interfacial tension and forming a rigid, elastic film that hinders droplet coalescence. This results in the creation of finely dispersed oil droplets within the aqueous phase. The reduction in average droplet size directly contributes to a substantial decrease in the apparent viscosity of the heavy oil, as described by the relationship between emulsion microstructure and bulk flow behavior . Figure 8 presents the viscosity reduction rates of three different heavy oil samples (A, B, and C) after a 24-hour aquathermolysis reaction at 150°C, using various magnetic emulsifiers at a mass fraction of 0.5%. In the absence of any emulsifier, the viscosity of all three heavy oils decreases only moderately under sole aquathermolysis conditions, indicating that thermal cracking alone has a limited effect on viscosity reduction. In contrast, the addition of emulsifiers leads to a marked enhancement in viscosity reduction. Among all tested formulations, ME-8 demonstrates superior performance​ in reducing the viscosity of each heavy oil sample compared to both more hydrophobic (ME-4, ME-6) and more hydrophilic (ME-10, ME-12) counterparts.This pronounced efficacy of ME-8 can be attributed to its optimized amphiphilic balance, achieved at a SiO₂/HMDS molar ratio of 8:1. Such balanced wettability enables ME-8 nanoparticles to exhibit high interfacial activity, accumulate strongly at the oil–water interface, and effectively reduce the interfacial tension, thereby improving emulsification efficiency and enhancing viscosity reduction. Moreover, the magnetic core allows the emulsifier to be dynamically concentrated at the reaction interface under the influence of external forces or recycled post-reaction, further boosting the catalytic aquathermolysis process and operational efficiency . Under optimal experimental conditions for the aquathermolysis reaction (emulsifier mass fraction: 0.5%; reaction temperature: 150°C; reaction time: 24 h), the amphiphilic emulsifier ME-8, with an SiO₂/HMDS molar ratio of 8:1, significantly reduced the apparent viscosity of three heavy oil samples (with initial viscosities of 27,500 cP, 58,000 cP, and 85,400 cP) from the Shengli Oilfield (Dongying, China) by 67.27%, 68.96%, and 56.67%, respectively. These results demonstrate its promising potential for downhole upgrading of heavy crude oils. Table 1 presents the SARA (saturated hydrocarbons, aromatics, resins, and asphaltenes) compositions of the tested heavy oils before and after the emulsion aquathermolysis reaction. It is evident that the asphaltene content in samples B and C is higher than that in sample A, which correlates well with their greater initial viscosities. After 24 hours of emulsion aquathermolysis at 150°C with 0.5% ME-8 emulsifier, the proportions of saturated and aromatic hydrocarbons increased, while the contents of resins and asphaltenes decreased. This indicates that the heavy components were effectively pyrolyzed into lighter components during the reaction. Table 1 The saturated hydrocarbon, aromatic hydrocarbon, resin and asphalt (expressed as SARA) compositions of the tested heavy oils before and after aquathermolysis reaction. Heavy oil samples Constituent (mass fraction, %) Saturated hydrocarbon Aromatic hydrocarbon Asphalt Resin A A + ME-8 B 26.94 30.34 23.66 27.85 32.65 29.36 9.56 8.54 14.75 35.65 28.47 32.23 B + ME-8 26.34 32.31 12.56 28.79 C 29.14 22.43 19.46 28.97 C + ME-8 31.86 26.35 16.37 25.42 The viscosity reduction of heavy oils is primarily governed by two synergistic mechanisms: emulsification​ and aquathermolysis. The ME-8 magnetic emulsifier, functionalized with hydrophilic silanol groups and hydrophobic trimethylsilyl groups, exhibits amphiphilic characteristics that allow it to disperse effectively at the interface between asphaltene aggregates and resin layers in the heavy oil matrix. This interfacial activity disrupts the native associative structure of heavy oil components, leading to the breakdown of rigid aggregates into looser, more mobile configurations. Within the heavy oil system, asphaltene supramolecules form micellar cores that strongly adsorb aromatic compounds and macromolecular resins through hydrogen bonding and π–π interactions, contributing to high viscosity. During the emulsion aquathermolysis process, the alkyl chains of ME-8 nanoparticles encapsulate asphaltene clusters, while the polar silanol groups interfere with the asphaltene layers, generating a shielding effect that establishes a non-polar microenvironment around the asphaltenes. This suppresses the recombination of asphaltenes with aromatic compounds, downgrades the supramolecular network, and releases trapped liquid hydrocarbons from the micellar structures (Fig. 9 a). As a result, the average size of the supramolecular assemblies is reduced, leading to a significant decrease in viscosity. Figure 9 b schematically illustrates the integrated emulsion aquathermolysis process.under elevated temperature and aqueous conditions, the aquathermolysis reaction is catalyzed by the magnetic nanoparticles. Steam and the emulsifier preferentially interact with heteroatoms (such as S, N, and O) present in heavy oil molecules, facilitating the cleavage of side chains and bridging bonds. Simultaneously, C–R bonds (where R = S, N, O, or C) are broken, generating lighter molecules including alkanes, ethers, thioethers, and amines, which further contribute to viscosity reduction. In summary, the novel magnetic emulsifier Fe₃O₄@SiO₂-HMDS not only significantly reduces the viscosity of heavy oil through the combined effects of emulsification and catalytic aquathermolysis but also allows for efficient recovery and potential reuse via magnetic separation, highlighting its practical potential in heavy oil exploitation . 4 Conclusions In this study, novel Fe₃O₄@SiO₂-HMDS magnetic emulsifiers were prepared by grafting hydrophobic hexamethyldisilazane (HMDS) onto the surface of Fe₃O₄@SiO₂ nanoparticles. These emulsifiers significantly enhanced the aquathermolysis reaction of heavy oils. The as-synthesized nanoparticles, with an average size of approximately 100 nm, exhibited good dispersion in oil and strong magnetic responsiveness, allowing easy recovery via magnetic separation. Particularly, the ME-8 emulsifier, possessing an optimal balance of hydrophilic silanol groups and hydrophobic trimethylsilyl groups, facilitated effective dispersion between asphaltene molecules and resin layers within the heavy oil matrix. Under optimized reaction conditions (emulsifier mass fraction: 0.5%; temperature: 150°C; time: 24 h), ME-8 efficiently promoted the aquathermolysis process, reducing the apparent viscosity of three types of heavy oils by 67.27%, 68.96%, and 56.67%, respectively. Therefore, we have developed a facile and novel synthesis method for magnetic emulsifiers, demonstrating promising potential for efficient heavy oil viscosity reduction. Declarations Acknowledgment: This work was financially supported by the National Natural Science Foundation of China (grant nos. 22102004), the National Postdoctoral Program for Innovative Talents (grant no. BX20200026), and the Fundamental Research Funds of Shaanxi Polytechnic University. Author contributions Yaoyao Feng : Investigation, Experimental data collection. Xiaoxun Li: Conceptualization, Formal analysis, Funding acquisition, Writing-review & editing. Funding This work was financially supported by the National Natural Science Foundation of China (grant nos. 22102004), the National Postdoctoral Program for Innovative Talents (grant no. BX20200026), and the Fundamental Research Funds of Shaanxi Polytechnic University. Data availability The author confirms that the data supporting the find[1]ings of this study are available within the article. Data will be made available on request. Conflict of interest There are no conflicts to declare. Ethics and Consent to Participate Not applicable. Consent to publish Not applicable. References Ahmadi M, Chen Z (2020) Challenges and future of chemical assisted heavy oil recovery processes. Adv. 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Energy Fuels 39(35): 16628-16651. https://doi.org/10.1021/acs.energyfuels.5c02478 Lu Y, Li R, Manica R, Liu Q, Xu Z (2020) Enhancing oil-solid and oil-water separation in heavy oil recovery by CO2-responsive surfactants. AIChE J. 67(1): e17033. https://doi.org/10.1002/aic.17033 Li Z, Lu, Y, Huang R, Chang J, Yu X, Jiang R, Yu X, Roskilly A (2021) Applications and technological challenges for heat recovery, storage and utilisation with latent thermal energy storage. Appl. Energy 283(1): 116277. https://doi.org/10.1016/j.apenergy.2020.116277 Melle S, Lask M, Fuller G (2005) Pickering Emulsions with Controllable Stability. Langumir 21(6): 215-2162. https://doi.org/10.1021/la047691n Nadarajah N, Singh A, Ward O (2002) De-emulsification of petroleum oil emulsion by a mixed bacterial. Culture. Process Biochem. 37(10): 1135-1141. https://doi.org/10.1016/S0032-9592(01)00325-9 Nguyen D, Balsamo V (2013) Emulsification of heavy oil in aqueous solutions of poly(vinylalcohol): a method for reducing apparent viscosity of production fluids. Energy Fuels 27(4): 1736-1747. https://doi.org/10.1021/ef3014986 Peng J, Liu Q, Xu Z, Masliyah J (2012) Synthesis of interfacially active and magnetically responsive nanoparticles for multiphase separation applications. Adv. Funct. Mater. 22(8): 1732-1740. https://doi.org/10.1002/adfm.201102156 Pratama R, Babadagli T (2022) A review of the mechanics of heavy-oil recovery by steam injection with chemical additives. J Petrol. Sci. Eng. 208: 109717. https://doi.org/10.1016/j.petrol.2021.109717 Sajid M, Shuja S, Rong H, Zhang J (2023) Size-controlled synthesis of Fe 3 O 4 and Fe 3 O 4 @SiO 2 nanoparticles and their superparamagnetic properties tailoring. Prog. Nat. Sci-Mater. 33(1): 116-119. https://doi.org/10.1016/j.pnsc.2022.08.003 Sakkaf M, Onaizi S (2024) Effects of emulsification factors on the characteristics of crude oil emulsions stabilized by chemical and Biosurfactants: A review. Fuel 361(1): 130604. https://doi.org/10.1016/j.fuel.2023.130604 Santos R, Loh W, Bannwart A, Trevisan O (2014) An overview of heavy oil properties and its recovery and transportation methods. Braz. J. Chem. Eng. 31(3): 571-590. https://doi.org/10.1590/0104-6632.20140313s00001853 Sun H, Wang H, Cao X, Shu Q, Fan Z, Wu G, Yang Y, Wu Y (2024) Innovations and applications of the thermal recovery techniques for heavy oil. Energy Geosci. 5(4): 100332. https://doi.org/10.1016/j.engeos.2024.100332 Sun W, Sun W, Kessler M, Bowler N, Dennis K, McCallum R, Li Q, Tan X (2013) Multifunctional properties of cyanate ester composites with SiO 2 coated Fe 3 O 4 fillers. ACS Appl. Mater. Interfaces 5(5): 1636-1642. https://doi.org/10.1021/am302520e Wu B, Xiu J, Yu L, Huang L, Yi L, Ma Y (2022) Research advances of microbial enhanced oil recovery. Heliyon 8(11): e11424. https://doi.org/10.1016/j.heliyon.2022.e11424 Xiong R, Guo J, Kiyingi W, Gao C, Wang L, Luo J, Song H, Wang X (2024) Technical transformation of heavy/ultra-heavy oil production in China driven by low carbon goals: A review. J. Clean. Prod. 458(15): 142531. https://doi.org/10.1016/j.jclepro.2024.142531 Xue L, Liu P, Zhang Y (2022) Development and research status of heavy oil enhanced oil recovery. Geofluids 2022: 5015045. https://doi.org/10.1155/2022/5015045 Yan N, Gray M, Masliyah J (2001) On water-in-oil emulsions stabilized by fine solids. Colloid Surf. Physicochem. Eng. Asp. 193(1): 97-107. https://doi.org/10.1016/S0927-7757(01)00748-8 Yao Y, Sun D, Xu J, Wang B, Peng G, Sun B (2023) Evaluation of enhanced oil recovery methods for mature continental heavy oil fields in China based on geology, technology and sustainability criteria. Energy 278: 127962. https://doi.org/10.1016/j.energy.2023.127962 Zhang L, Gao Z, Liu Y, Li Y, Zhou K, Wang P, Zhang K, Wang C, Zhang M (2025) Study on rapid screening method for different chemical flooding methods in heavy-oil reservoirs. Processes 13(9): 2992. https://doi.org/10.3390/pr13092992 Zhang X, Guo J, Fei D, Wang L, Peng Z, Li J, Dong J (2024) Polymer surfactants as viscosity reducers for ultra-heavy oil: Synthesis and viscosity reduction mechanism. Fuel 357: 129871. https://doi.org/10.1016/j.fuel.2023.129871 Zhao H, Kang W, Yang H, Huang Z, Zhou B, Sarsenbekuly B (2020) Emulsification and stabilization mechanism of crude oil emulsion by surfactant synergistic amphiphilic polymer system. Colloid Surf. Physicochem. Eng. Asp. 609(20): 125726. https://doi.org/10.1016/j.colsurfa.2020.125726 Zhu Y, Jiang J, Liu K, Cui Z, Binks B (2015) Switchable pickering emulsions stabilized by silica nanoparticles hydrophobized in situ with a conventional cationic surfactant. Langmuir 31(11): 3301-3307. https://doi.org/10.1021/acs.langmuir.5b00295 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 09 Apr, 2026 Reviews received at journal 25 Feb, 2026 Reviews received at journal 20 Feb, 2026 Reviews received at journal 12 Feb, 2026 Reviewers agreed at journal 10 Feb, 2026 Reviewers agreed at journal 09 Feb, 2026 Reviewers agreed at journal 08 Feb, 2026 Reviewers agreed at journal 08 Feb, 2026 Reviews received at journal 06 Feb, 2026 Reviewers agreed at journal 06 Feb, 2026 Reviewers invited by journal 06 Feb, 2026 Editor assigned by journal 06 Feb, 2026 Submission checks completed at journal 03 Feb, 2026 First submitted to journal 02 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8769823","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":589024707,"identity":"d6bf5348-9865-4171-acb1-7a84baaf2816","order_by":0,"name":"Yaoyao Feng","email":"","orcid":"","institution":"Shaanxi Polytechnic University","correspondingAuthor":false,"prefix":"","firstName":"Yaoyao","middleName":"","lastName":"Feng","suffix":""},{"id":589024708,"identity":"c9d93b2c-1c7a-48ba-ad8d-b98c84155363","order_by":1,"name":"Xiaoxun Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA40lEQVRIie3SsQqCQBjA8ZODc/my9Q4jX+FEaOphLlobhKA1QbBX0LeoNygcbolaHRoKweYImho6S4KW07Hh/iCfy48P70TIZPrH8GcMiB2pwdWz7UiAwLYraQJERfPaRrjEl7KXnMBh18oNQzR0CmHdQw1hMQn8LKmAuLMgSDkKWCGwm2pIH6MRvSV5TawSOJqsC0EwaAjB9oNOasLkOVdk2Ur6GJotFPn1FsHbCIth7qcHReD9LdTP9pfY1RF+lJsSFvnQW0l1Ys+x58jp7q4jP6lrpWpYUVfw/RNMJpPJ9NsLvUM/YF/vf8YAAAAASUVORK5CYII=","orcid":"","institution":"Shaanxi Polytechnic University","correspondingAuthor":true,"prefix":"","firstName":"Xiaoxun","middleName":"","lastName":"Li","suffix":""}],"badges":[],"createdAt":"2026-02-03 01:53:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8769823/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8769823/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102745599,"identity":"70c52329-8876-4dd8-80b9-46daedaa176e","added_by":"auto","created_at":"2026-02-16 08:52:39","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":169188,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic illustration of the routes to preparing Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e-HMDS nanoparticles. (b) The oil reducing process via the novel emulsifier.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8769823/v1/01906cac60247ab1d902917c.png"},{"id":102420229,"identity":"59eaeeb2-56b8-47ed-91ed-7ab837c91a58","added_by":"auto","created_at":"2026-02-11 13:34:28","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":373674,"visible":true,"origin":"","legend":"\u003cp\u003eTEM images of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e ((a) and (b)) and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e-HMDS ((c) and (d)) nanoparticles.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8769823/v1/c109fbc090fa7684e5526eb6.png"},{"id":102420221,"identity":"e2ac9798-9443-4362-8e0b-1aa93007d522","added_by":"auto","created_at":"2026-02-11 13:34:28","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":58558,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of various as-prepared magnetic nanoparticles.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8769823/v1/77599027b4d4c692d6b11c5e.png"},{"id":102745485,"identity":"f8b88231-fa85-4d92-b3a6-d322dc3ff332","added_by":"auto","created_at":"2026-02-16 08:51:06","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":39898,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of ME-0 and ME-8.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8769823/v1/ecc427ddec35e9e1a86d0b55.png"},{"id":102962237,"identity":"f66d03ff-49ef-418c-8943-47611c7221c9","added_by":"auto","created_at":"2026-02-19 04:05:56","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":172298,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The optical photos of the emulsifiers, a: ME-4, b: ME-6, c: ME-8, d: ME-10 and :e: ME-12 (b)Water contact angle measurements of compressed magnetic\u003cstrong\u003e \u003c/strong\u003ecomposite disks corresponding to the emulsifiers, a:160\u003csup\u003eo\u003c/sup\u003e, b: 145\u003csup\u003eo\u003c/sup\u003e, c: 80\u003csup\u003eo\u003c/sup\u003e, d: 0\u003csup\u003eo \u003c/sup\u003eand e: 0\u003csup\u003eo \u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8769823/v1/5235ea324a06338ee8d11ba3.png"},{"id":103049213,"identity":"44bce9d0-f757-4e0f-8b99-2bec7ee54add","added_by":"auto","created_at":"2026-02-20 07:38:22","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":54377,"visible":true,"origin":"","legend":"\u003cp\u003eThe magnetic hysteresis loops of pure ME-8. The inset is the effect of external magnetic field on the dispersion of magnetic emulsifier ME-8 in diesel.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8769823/v1/3bb46fa5bad55f10375339cd.png"},{"id":102745893,"identity":"f1a59aee-9ea3-4201-85d0-fab0a358b4d1","added_by":"auto","created_at":"2026-02-16 08:54:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":103726,"visible":true,"origin":"","legend":"\u003cp\u003eThe\u003cstrong\u003e \u003c/strong\u003eillustration of emulsification mechanism of the novel Fe3O4@SiO2-HMD emulsifier.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8769823/v1/912a94cac7f0d6b9e529cb3b.png"},{"id":102420227,"identity":"aa8db084-2e9b-4d17-9b05-89ac841f47cd","added_by":"auto","created_at":"2026-02-11 13:34:28","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":23243,"visible":true,"origin":"","legend":"\u003cp\u003eViscosity reduction rate of heavy oil samples A, B and C after 24 h of aquathermolysis reaction at 150 \u003csup\u003eo\u003c/sup\u003eC in the presence of various magnetic emulsifiers.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8769823/v1/dc7df0cf17f40c6870897c0d.png"},{"id":102420228,"identity":"87126546-7aa2-4d45-85ed-50170d204d9a","added_by":"auto","created_at":"2026-02-11 13:34:28","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":22777,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic process of emulsion aquathermolysis.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-8769823/v1/6a41ff0b998aa8ab86691a38.png"},{"id":103503864,"identity":"d1ea8a33-0b07-4664-a057-083d3150b627","added_by":"auto","created_at":"2026-02-26 13:03:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1714838,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8769823/v1/d5b2cb53-3ba8-4141-a0e9-dd66ff02d5f1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eFe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e @SiO\u003csub\u003e2\u003c/sub\u003e -hexamethyldisilazane amphiphilic magnetic emulsifier for viscosity-reduction of heavy oils via aquathermolysis reaction\u003c/p\u003e","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eHeavy oil, which constitutes a large portion of the world's proven oil reserves, serves as a major source of hydrocarbon energy. However, its high viscosity and high freezing point pose significant challenges to extraction and transportation (Santos et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Xiong et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Xue et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Nguyen et al. 2013; Karimov et al. 2024). Currently, most of the confirmed large deposits of bitumen and heavy oil are located in Venezuela, Canada, and the United States. In China, the proven and controlled heavy oil reserves amount to approximately 1.6\u0026nbsp;billion tons, accounting for about 30% of the world\u0026rsquo;s total heavy oil reserves. Compared with conventional crude oil, heavy oil contains a higher proportion of long-chain and cyclic hydrocarbons (Zhao et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Ashrafizadeh et al. 2010; Hannisdal et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). These components contribute to its high viscosity, high density, and poor flowability, making extraction particularly difficult (Liu et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Pratama et al. 2022; He et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Yao et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Therefore, reducing viscosity and enhancing mobility are crucial for the effective exploitation of heavy oil resources and there is an urgent need to develop novel and efficient viscosity-reduction methods to improve heavy oil production .\u003c/p\u003e \u003cp\u003eOver the years, numerous techniques including thermal (Khelkhal et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Bueno et al. 2022; Sun et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), chemical (Chen et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Ding et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Ahmadi et al. 2024; Liu et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Zhang et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Zhang et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), microbial recovery (Liurdes et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Wu et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Nadarajah et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2002\u003c/span\u003e), Nanoparticals (Al-Janabi et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Sun et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Sajid et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) other methods (Binks et al. 2007; Chen et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Lu et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) have been developed for heavy oil exploitation. For example, chemically induced oil-in-water (O/W) emulsions emerged as a potential means to reduce the viscosity of produced fluids (Al-Sabagh et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Liang et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Ali et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Peng et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Zhu et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). When low molecular-weight surfactants and water are injected into the flow system, the resulting O/W emulsion is particularly significant for the low-cost extraction of heavy oil due to its substantial viscosity reduction effect. However, the application of O/W emulsions in promoting the aquathermolysis of heavy oil remains limited, primarily due to the difficulty in breaking these emulsions. Traditionally, fine solids with appropriate surface wettability, such as montmorillonite, sandstone, alumina, clay, Ca(OH)₂, and silica, can stabilize emulsions and help them retain desired properties in produced fluids (Yan et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Melle et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Jiang et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Binks et al. 2006). This stability is especially important in unconventional petroleum production. Therefore, the study of interfacial properties in particle-stabilized petroleum emulsions deserves special attention. For instance, Ramsden and Pickering prepared emulsions with long-term stability and found that particles with a solid\u0026ndash;liquid contact angle close to 90\u0026deg; are most effective in stabilizing O/W emulsions (Liang et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).[35] Jung et al. suggested that silica nanoparticles are among the most promising nanomaterials for oil recovery because their oil compatibility can be greatly enhanced through surface modification with silane (Jung et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Although such emulsions can improve heavy oil production efficiency, breaking these highly stable emulsions remains a major challenge during crude oil refining. To address this bottleneck, researchers have developed magnetite nanoparticles as demulsifiers that can be activated by an external magnetic field. These magnetic sub-micron particles can be easily recycled via magnetic separation and solvent washing, while the external field enhances the coalescence of magnetically tagged water droplets within the emulsion.\u003c/p\u003e \u003cp\u003eHere, our study focuses on the application of magnetic nanoparticles for stabilizing emulsions and reducing the viscosity of heavy oil. We grafted HMDS (hexamethyldisilazane), a hydrophobic modifying agent, onto the surface of magnetic Fe₃O₄@SiO₂ nanoparticles to synthesize a novel magnetic emulsifier, Fe₃O₄@SiO₂-HMDS. This emulsifier demonstrated remarkable performance in reducing the viscosity of three types of extra-heavy oil during an aquathermolysis process simulated using a rolling apparatus to mimic flow conditions. The reduction in viscosity is attributed to the ability of the magnetic nanoparticles to promote the formation of stable oil-in-water (O/W) Pickering emulsions. The amphiphilic emulsifier ME-8, with an optimal SiO₂/HMDS molar ratio of 8:1, significantly reduced the apparent viscosity of heavy oil samples (initial viscosities: 27,500 cP, 58,000 cP, and 85,400 cP) by 67.27%, 68.96%, and 56.67%, respectively. These results were achieved under the following optimized conditions: emulsifier mass fraction of 0.5%, reaction temperature of 150\u0026deg;C, and reaction time of 24 h. In addition to its high efficiency in viscosity reduction, the Fe₃O₄@SiO₂-HMDS emulsifier can be easily recovered via magnetic separation due to its superparamagnetic properties, enabling recyclability and reducing operational costs. The combination of significant viscosity reduction and straightforward recovery highlights the potential of this magnetic emulsifier in sustainable heavy oil exploitation.\u003c/p\u003e"},{"header":"2 Material and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eFerric chloride hexahydrate (FeCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO, analytical grade reagent (AR)), ethylene glycol ((CH\u003csub\u003e2\u003c/sub\u003eOH)\u003csub\u003e2\u003c/sub\u003e, AR), sodium citrate (Na\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO, AR), sodium acetate (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003eNaO\u003csub\u003e5\u003c/sub\u003e, AR), and ammonium chloride (NH\u003csub\u003e4\u003c/sub\u003eCl, AR) were purchased from Tianjin Kemiou Chemical Reagent Technology Company Ltd (Tianjin, China). Polyethylene glycol (HO(CH\u003csub\u003e2\u003c/sub\u003eCH\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e\u003cem\u003en\u003c/em\u003e\u003c/sub\u003eH, molecular weight 4000, AR) was commercially obtained from Tianjin Fuyu Fine Chemical Company Ltd (Tianjin, China). Sodium silicate (Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO) was provided by Kaifeng Dongda Chemical Company Ltd (Kaifeng, China). 1,1,1,3,3,3-hexamethyldisilazane (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e19\u003c/sub\u003eNSi\u003csub\u003e2\u003c/sub\u003e, AR) was purchased from Hangzhou Guibao Chemical Company Ltd (Hangzhou, China). Industrial alcohol was provided by Tianjin Chengtongtai Chemical Company Ltd (Tianjin, China). The three kinds of heavy oil samples (viscosity at 50 \u003csup\u003eo\u003c/sup\u003eC: 27500 cP, 58000cP and 85400cP), coded as oil samples A, B and C, respectively, were produced at Shengli Oilfield (Dongying, China).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e-HMDS magnetic emulsifier\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea schematically illustrates the preparation route of the Fe₃O₄@SiO₂-HMDS magnetic emulsifier. Briefly, core\u0026ndash;shell structured Fe₃O₄ spheres were synthesized via a coprecipitation method, followed by coating with a SiO₂ layer using a modified St\u0026ouml;ber method. The as-prepared Fe₃O₄@SiO₂ nanoparticles were retained in the reactor, and HMDS was gradually introduced to form a suspension. This suspension was then heated to 70\u0026deg;C and maintained at this temperature for 2 h, after which it was filtered. The filtered cake was repeatedly washed with deionized water until no Cl⁻ could be detected using aqueous silver nitrate. Finally, the product was vacuum-dried overnight to obtain the target Fe₃O₄@SiO₂-HMDS composite nanoparticles. By varying the molar ratio of silicon dioxide to HMDS as 4:1, 6:1, 8:1, 10:1, and 12:1, while keeping other parameters constant\u0026mdash;a series of corresponding magnetic emulsifiers (abbreviated as ME-4, ME-6, ME-8, ME-10, and ME-12) were obtained. This approach allows for a balance between hydrophilic silanol groups and hydrophobic trimethylsilyl groups. As a result, the emulsifier exhibits improved dispersion at the oil\u0026ndash;water interface and enhanced emulsifying capability.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Evaluation of viscosity-reducing performance of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e-HMDS magnetic emulsifiers for the aquathermolysis reaction of heavy oils\u003c/h2\u003e \u003cp\u003eThe viscosity reduction performance of the magnetic emulsifiers, prepared for the hydrothermal cracking reaction of three heavy oils, was evaluated using an LHG-3 autoclave reactor (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Briefly, 100 g of heavy oil, 50 g of deionized water, and 0.5 g of the as-synthesized magnetic emulsifier were placed into the reactor. The mixture was heated to 150\u0026deg;C and maintained at that temperature for 24 hours to complete the aquathermolysis reaction. After the reaction, the system was allowed to cool naturally to room temperature.The viscosity of the oil samples before and after aquathermolysis was measured at 50\u0026deg;C using a Brookfield DV-III programmable viscometer. The viscosity reduction ratio was calculated as follows:\u003c/p\u003e \u003cp\u003eΔη = (η₀ \u0026minus; η) / η₀ \u0026times; 100% (1)\u003c/p\u003e \u003cp\u003ewhere Δη (%) represents the viscosity reduction ratio, η₀ (cP) is the viscosity of the original heavy oil, and η (cP) is the viscosity of the heavy oil after the emulsion aquathermolysis reaction. In addition, column chromatographic separation was performed in accordance with the Chinese petroleum industry standard SY/T 5119\u0026thinsp;\u0026minus;\u0026thinsp;2008 to isolate four components, saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltenes (collectively referred to as SARA), from the oil samples.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Characterization of magnetic emulsifier\u003c/h2\u003e \u003cp\u003eAs-prepared Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e-HMDS magnetic emulsifiers were characterized by transmission electron microscopy (TEM; JEM 2010; JEOL, Japan), X-ray diffraction (XRD; Bruker XRD D8 Advance diffractometer, Bruker Spectrum Instrument Company, Germany), and Fourier transform infrared spectroscopy (FTIR; AVATAR-360, Nigaoli Instrument Company, USA; wavenumber range 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3.1 Characterization of as-prepared Fe\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO\u003c/b\u003e\u003csub\u003e\u003cb\u003e4\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e@SiO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e-HMDS magnetic emulsifier\u003c/b\u003e\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents TEM images of the as-prepared Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂-HMDS composite nanoparticles. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, the Fe₃O₄@SiO₂ nanoparticles exhibit a spherical morphology with diameters ranging from 90 to 100 nm; however, a significant degree of aggregation is observed among these particles. This aggregation can be attributed to the presence of active surface silanol (\u0026ndash;SiOH) groups, which promote interparticle hydrogen bonding and van der Waals interactions, leading to the assembly of individual nanoparticles into larger clusters. In contrast, after modification with HMDS, the Fe₃O₄@SiO₂-HMDS nanoparticles maintain their spherical shape but show a slight increase in diameter and a remarkable improvement in dispersibility, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed. The grafting of hydrophobic trimethylsilyl groups via HMDS replaces the hydrophilic surface hydroxyl groups, thereby introducing steric hindrance that reduces particle\u0026ndash;particle adhesion and agglomeration tendencies. As a result, the modified nanoparticles are better stabilized in organic media, and their crystal growth proceeds in a more controlled manner, yielding well-dispersed and structurally well-defined nanoparticles suitable for application in Pickering emulsion systems and interfacial catalysis .\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents the XRD patterns of the ME-4, ME-6, ME-8, ME-10, and ME-12 magnetic nanoparticles. The weak and broad diffraction features observed in the 2θ range of 20\u0026deg;\u0026ndash;30\u0026deg; correspond to amorphous silica (SiO₂), which is consistent with the typical characteristics of a non-crystalline SiO₂ coating. The intensity of this amorphous hump gradually decreases from ME-4 to ME-12, and it is weakest in the ME-0 sample (unmodified Fe₃O₄@SiO₂). This trend suggests that as the HMDS-to-SiO₂ ratio increases, the surface modification influences the long-range ordering of the silica shell, leading to a progressively less distinct amorphous signal. Simultaneously, the distinct diffraction peaks observed at 2θ values of 30.12\u0026deg;, 37.12\u0026deg;, 43.12\u0026deg;, 53.40\u0026deg;, 57.02\u0026deg;, and 62.56\u0026deg; are readily indexed to the (220), (311), (400), (422), (511), and (440) crystal planes, respectively, of magnetite (Fe₃O₄) with an inverse cubic spinel structure (JCPDS card no. 65-3107). This confirms that the core magnetic phase remains intact throughout the synthesis and modification process. When compared to the unmodified Fe₃O₄@SiO₂ (ME-0), the Fe₃O₄@SiO₂-HMDS samples exhibit a noticeable weakening in the intensity of these characteristic Fe₃O₄ peaks. This attenuation indicates that the surface capping by HMDS introduces a certain degree of structural distortion or reduces the coherent scattering domain size at the crystal surface, leading to a measurable reduction in the apparent crystallinity of the magnetite phase. However, the fact that the peak positions remain unchanged confirms that the underlying crystal structure of the ferrimagnetic Fe₃O₄ core is not altered by the hydrophobic surface modification, preserving the essential magnetic properties of the nanoparticles .\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e presents the Fourier Transform Infrared Spectroscopy (FTIR) spectra of ME-8 and the unmodified reference sample ME-0 (Fe₃O₄@SiO₂). The spectrum of ME-0 exhibits characteristic absorption bands at 1096 cm⁻\u0026sup1; and 797 cm⁻\u0026sup1;, which are attributed to the anti-symmetric stretching vibration and bending vibration of the Si\u0026ndash;O\u0026ndash;Si framework, respectively, confirming the formation of a silica (SiO₂) coating on the magnetic nanoparticles. Additionally, broad absorption bands observed at 3427 cm⁻\u0026sup1; and 1634 cm⁻\u0026sup1; correspond to the O\u0026ndash;H stretching vibration and H\u0026ndash;O\u0026ndash;H bending vibration of adsorbed water molecules, indicating the presence of surface silanol (Si\u0026ndash;OH) groups and physisorbed water in the as-synthesized composites. The presence of these hydroxyl groups is consistent with the hydrophilic nature of the unmodified silica surface, which tends to form hydrogen-bonded silanol nests that strongly adsorb water. In contrast, the spectrum of ME-8 shows additional peaks at 2966 cm⁻\u0026sup1;, 1254 cm⁻\u0026sup1;, and 845 cm⁻\u0026sup1;, which are assigned to the symmetric and asymmetric stretching vibrations of C\u0026ndash;H bonds in \u0026ndash;CH₃ groups and the stretching vibration of Si\u0026ndash;C bonds, respectively. These features indicate the successful grafting of hexamethyldisilazane (HMDS) onto the silica surface, where the hydrophobic trimethylsilyl groups (\u0026ndash;Si(CH₃)₃) have replaced the original hydrophilic silanol groups via covalent bonding. The reduction in intensity of the O\u0026ndash;H stretching band at 3427 cm⁻\u0026sup1; further supports the effective surface modification, confirming that HMDS capping reduces surface hydrophilicity and enhances the compatibility of the nanoparticles with organic media such as heavy oil. This covalent functionalization not only improves the dispersion of nanoparticles at the oil-water interface but also contributes to the amphiphilic character of the ME-8 emulsifier, which is essential for stabilizing Pickering emulsions and facilitating the aquathermolysis process during viscosity reduction.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further evaluate the hydrophobic characteristics of the magnetic emulsifiers, emulsions of ME-4, ME-6, ME-8, ME-10, and ME-12 were prepared using a rolling machine at room temperature, with the magnetic emulsifier concentration fixed at 4 \u0026times; 10⁻\u0026sup3; g/L. The state of the resulting emulsions was observed using a digital camera. Concurrently, the water contact angles on the surfaces of compressed magnetic composite disks were measured using a solid\u0026ndash;liquid interface analyzer (DM300, Kyowa Interface Science Co., Ltd., Japan) to quantitatively assess their wettability. As shown in \u003cb\u003eFig.\u0026nbsp;5a\u003c/b\u003e, ME-4 and ME-6 powders, exhibiting strong hydrophobicity, float entirely on the water surface, whereas ME-10 and ME-12 powders are completely dispersed in the aqueous phase. ME-8 presents an intermediate behavior: a portion of the powder floats while the emulsion appears somewhat turbid. Correspondingly, the water contact angles measured for ME-4, ME-6, ME-8, ME-10, and ME-12 are approximately 160\u0026deg;, 145\u0026deg;, 80\u0026deg;, 0\u0026deg;, and 0\u0026deg;, respectively (Fig.\u0026nbsp;5b). These results clearly indicate that as the HMDS dosage increases, the hydrophobicity of the Fe₃O₄@SiO₂ nanoparticles is significantly enhanced due to the progressive replacement of hydrophilic silanol groups (─SiOH) on the silica surface with hydrophobic trimethylsilyl groups (─Si(CH₃)₃) introduced by HMDS. The contact angle, as described by the Young-Laplace equation, reflects the balance of interfacial tensions at the solid\u0026ndash;liquid\u0026ndash;gas boundary, and its variation here directly correlates with the changing surface chemistry of the nanoparticles. It can therefore be inferred that surface modification with HMDS effectively tunes the wettability of the nanoparticles from hydrophilic to highly hydrophobic. As the SiO₂/HMDS molar ratio decreases from ME-12 to ME-4, the increasing coverage of trimethylsilyl groups reduces the surface free energy and enhances the affinity toward oil phases. ME-8, with its balanced composition, possesses both residual hydrophilic silanol groups and grafted hydrophobic trimethylsilyl groups, rendering it amphiphilic. This amphiphilic character allows ME-8 to act as an effective surfactant, facilitating the stabilization of oil, water interfaces, crucial for forming and stabilizing Pickering emulsions in heavy oil aquathermolysis processes\u003c/p\u003e \u003cp\u003e.\u003c/p\u003e \u003cp\u003e \u003cb\u003eFigure 5.\u003c/b\u003e (a) The optical photos of the emulsifiers, a: ME-4, b: ME-6, c: ME-8, d: ME-10 and :e: ME-12 (b)Water contact angle measurements of compressed magnetic composite disks corresponding to the emulsifiers, a:160\u003csup\u003eo\u003c/sup\u003e, b: 145\u003csup\u003eo\u003c/sup\u003e, c: 80\u003csup\u003eo\u003c/sup\u003e, d: 0\u003csup\u003eo\u003c/sup\u003e and e: 0\u003csup\u003eo\u003c/sup\u003e .\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e presents the magnetic properties of the Fe₃O₄@SiO₂-HMDS microspheres measured at 300 K using a vibrating sample magnetometer (VSM). The saturation magnetization (Mₛ) value was determined to be 54.3 emu/g, which is lower than that of uncoated magnetite (typically\u0026thinsp;~\u0026thinsp;90 emu/g for bulk Fe₃O₄) due to the diamagnetic contribution of the SiO₂ shell and the surface grafting of HMDS, both of which reduce the overall magnetic moment per unit mass. This high Mₛ ensures strong magnetic responsiveness, critical for magnetic separation and guidance. To demonstrate this, Fe₃O₄@SiO₂-HMDS microspheres were dispersed in diesel with and without an external magnetic field. After vigorous shaking, they formed a stable brown suspension, confirming good dispersibility in the organic medium, enabled by hydrophobic HMDS surface modification. When a magnet was applied, the microspheres rapidly aggregated toward the field source, cleanly separating from the diesel. This fast response reflects strong magnetic dipole interactions, typical of ferrimagnetic Fe₃O₄ with single- or multi-domain cores. The combination of field-free dispersibility and field-triggered aggregation demonstrates excellent magnetic controllability, key for demulsification and enhanced oil recovery: the particles uniformly disperse in heavy oil emulsions to promote interfacial activity, then are efficiently recovered via magnetic separation after reducing viscosity, improving process efficiency and lowering operational costs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2 The effect of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e-HMDS magnetic emulsifiers on the aquathermolysis reaction of heavy oils\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e illustrates the proposed mechanism of the viscosity-reduction process utilizing the Fe₃O₄@SiO₂-HMDS magnetic emulsifier. In this system, the SiO₂ shell (bearing silanol groups, \u0026ndash;SiOH) serves as the hydrophilic moiety, while the long-chain HMDS grafted onto the surface acts as the hydrophobic moiety. When water and the emulsifier are introduced into the crude oil, the amphiphilic nature of the nanoparticles promotes the formation of oil-in-water (O/W) or water-in-oil (W/O) Pickering emulsions, depending on the three-phase contact angle, through vigorous shearing or rolling. The nanoparticles spontaneously migrate to and adsorb strongly at the oil\u0026ndash;water interface, significantly lowering the interfacial tension and forming a rigid, elastic film that hinders droplet coalescence. This results in the creation of finely dispersed oil droplets within the aqueous phase. The reduction in average droplet size directly contributes to a substantial decrease in the apparent viscosity of the heavy oil, as described by the relationship between emulsion microstructure and bulk flow behavior .\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003e presents the viscosity reduction rates of three different heavy oil samples (A, B, and C) after a 24-hour aquathermolysis reaction at 150\u0026deg;C, using various magnetic emulsifiers at a mass fraction of 0.5%. In the absence of any emulsifier, the viscosity of all three heavy oils decreases only moderately under sole aquathermolysis conditions, indicating that thermal cracking alone has a limited effect on viscosity reduction. In contrast, the addition of emulsifiers leads to a marked enhancement in viscosity reduction. Among all tested formulations, ME-8 demonstrates superior performance​ in reducing the viscosity of each heavy oil sample compared to both more hydrophobic (ME-4, ME-6) and more hydrophilic (ME-10, ME-12) counterparts.This pronounced efficacy of ME-8 can be attributed to its optimized amphiphilic balance, achieved at a SiO₂/HMDS molar ratio of 8:1. Such balanced wettability enables ME-8 nanoparticles to exhibit high interfacial activity, accumulate strongly at the oil\u0026ndash;water interface, and effectively reduce the interfacial tension, thereby improving emulsification efficiency and enhancing viscosity reduction. Moreover, the magnetic core allows the emulsifier to be dynamically concentrated at the reaction interface under the influence of external forces or recycled post-reaction, further boosting the catalytic aquathermolysis process and operational efficiency .\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUnder optimal experimental conditions for the aquathermolysis reaction (emulsifier mass fraction: 0.5%; reaction temperature: 150\u0026deg;C; reaction time: 24 h), the amphiphilic emulsifier ME-8, with an SiO₂/HMDS molar ratio of 8:1, significantly reduced the apparent viscosity of three heavy oil samples (with initial viscosities of 27,500 cP, 58,000 cP, and 85,400 cP) from the Shengli Oilfield (Dongying, China) by 67.27%, 68.96%, and 56.67%, respectively. These results demonstrate its promising potential for downhole upgrading of heavy crude oils. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents the SARA (saturated hydrocarbons, aromatics, resins, and asphaltenes) compositions of the tested heavy oils before and after the emulsion aquathermolysis reaction. It is evident that the asphaltene content in samples B and C is higher than that in sample A, which correlates well with their greater initial viscosities. After 24 hours of emulsion aquathermolysis at 150\u0026deg;C with 0.5% ME-8 emulsifier, the proportions of saturated and aromatic hydrocarbons increased, while the contents of resins and asphaltenes decreased. This indicates that the heavy components were effectively pyrolyzed into lighter components during the reaction.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe saturated hydrocarbon, aromatic hydrocarbon, resin and asphalt (expressed as SARA) compositions of the tested heavy oils before and after aquathermolysis reaction.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eHeavy oil samples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eConstituent (mass fraction, %)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSaturated hydrocarbon\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAromatic hydrocarbon\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAsphalt\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eResin\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA\u003c/p\u003e \u003cp\u003eA\u0026thinsp;+\u0026thinsp;ME-8\u003c/p\u003e \u003cp\u003eB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26.94\u003c/p\u003e \u003cp\u003e30.34\u003c/p\u003e \u003cp\u003e23.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.85\u003c/p\u003e \u003cp\u003e32.65\u003c/p\u003e \u003cp\u003e29.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9.56\u003c/p\u003e \u003cp\u003e8.54\u003c/p\u003e \u003cp\u003e14.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e35.65\u003c/p\u003e \u003cp\u003e28.47\u003c/p\u003e \u003cp\u003e32.23\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eB\u0026thinsp;+\u0026thinsp;ME-8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e28.79\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e28.97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u0026thinsp;+\u0026thinsp;ME-8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe viscosity reduction of heavy oils is primarily governed by two synergistic mechanisms: emulsification​ and aquathermolysis. The ME-8 magnetic emulsifier, functionalized with hydrophilic silanol groups and hydrophobic trimethylsilyl groups, exhibits amphiphilic characteristics that allow it to disperse effectively at the interface between asphaltene aggregates and resin layers in the heavy oil matrix. This interfacial activity disrupts the native associative structure of heavy oil components, leading to the breakdown of rigid aggregates into looser, more mobile configurations. Within the heavy oil system, asphaltene supramolecules form micellar cores that strongly adsorb aromatic compounds and macromolecular resins through hydrogen bonding and π\u0026ndash;π interactions, contributing to high viscosity. During the emulsion aquathermolysis process, the alkyl chains of ME-8 nanoparticles encapsulate asphaltene clusters, while the polar silanol groups interfere with the asphaltene layers, generating a shielding effect that establishes a non-polar microenvironment around the asphaltenes. This suppresses the recombination of asphaltenes with aromatic compounds, downgrades the supramolecular network, and releases trapped liquid hydrocarbons from the micellar structures (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003ea). As a result, the average size of the supramolecular assemblies is reduced, leading to a significant decrease in viscosity. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003eb schematically illustrates the integrated emulsion aquathermolysis process.under elevated temperature and aqueous conditions, the aquathermolysis reaction is catalyzed by the magnetic nanoparticles. Steam and the emulsifier preferentially interact with heteroatoms (such as S, N, and O) present in heavy oil molecules, facilitating the cleavage of side chains and bridging bonds. Simultaneously, C\u0026ndash;R bonds (where R\u0026thinsp;=\u0026thinsp;S, N, O, or C) are broken, generating lighter molecules including alkanes, ethers, thioethers, and amines, which further contribute to viscosity reduction. In summary, the novel magnetic emulsifier Fe₃O₄@SiO₂-HMDS not only significantly reduces the viscosity of heavy oil through the combined effects of emulsification and catalytic aquathermolysis but also allows for efficient recovery and potential reuse via magnetic separation, highlighting its practical potential in heavy oil exploitation .\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eIn this study, novel Fe₃O₄@SiO₂-HMDS magnetic emulsifiers were prepared by grafting hydrophobic hexamethyldisilazane (HMDS) onto the surface of Fe₃O₄@SiO₂ nanoparticles. These emulsifiers significantly enhanced the aquathermolysis reaction of heavy oils. The as-synthesized nanoparticles, with an average size of approximately 100 nm, exhibited good dispersion in oil and strong magnetic responsiveness, allowing easy recovery via magnetic separation. Particularly, the ME-8 emulsifier, possessing an optimal balance of hydrophilic silanol groups and hydrophobic trimethylsilyl groups, facilitated effective dispersion between asphaltene molecules and resin layers within the heavy oil matrix. Under optimized reaction conditions (emulsifier mass fraction: 0.5%; temperature: 150\u0026deg;C; time: 24 h), ME-8 efficiently promoted the aquathermolysis process, reducing the apparent viscosity of three types of heavy oils by 67.27%, 68.96%, and 56.67%, respectively. Therefore, we have developed a facile and novel synthesis method for magnetic emulsifiers, demonstrating promising potential for efficient heavy oil viscosity reduction.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment:\u0026nbsp;\u003c/strong\u003eThis work was financially supported by the National Natural Science Foundation of China (grant nos. 22102004), the National Postdoctoral Program for Innovative Talents (grant no. BX20200026), and the Fundamental Research Funds of Shaanxi Polytechnic University.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions Yaoyao Feng\u003c/strong\u003e: Investigation, Experimental data collection. Xiaoxun Li: Conceptualization, Formal analysis, Funding acquisition, Writing-review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e This work was financially supported by the National Natural Science Foundation of China (grant nos. 22102004), the National Postdoctoral Program for Innovative Talents (grant no. BX20200026), and the Fundamental Research Funds of Shaanxi Polytechnic University.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e The author confirms that the data supporting the find[1]ings of this study are available within the article. Data will be made available on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e There are no conflicts to declare.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics and Consent to Participate\u003c/strong\u003e\u0026ensp;\u0026nbsp;Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to publish\u003c/strong\u003e Not applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAhmadi M, Chen Z (2020) Challenges and future of chemical assisted heavy oil recovery processes. Adv. Colloid Interface Sci. 275: 102081. https://doi.org/10.1016/j.cis.2019.102081\u003c/li\u003e\n \u003cli\u003eAli N, Zhang B, Zhang H, Li W, Zaman W, Tian L, Zhang Q (2015) Novel Janus magnetic micro particle synthesis and its applications as a demulsifier for breaking heavy crude oil and water emulsion. 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Langmuir 31(11): 3301-3307. https://doi.org/10.1021/acs.langmuir.5b00295\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"brazilian-journal-of-chemical-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bjce","sideBox":"Learn more about [Brazilian Journal of Chemical Engineering](http://link.springer.com/journal/43153)","snPcode":"43153","submissionUrl":"https://www.editorialmanager.com/bjce/default2.aspx","title":"Brazilian Journal of Chemical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Heavy oil, Emulsifier, Fe3O4@SiO2-HMDS, Viscosity-reduction","lastPublishedDoi":"10.21203/rs.3.rs-8769823/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8769823/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHeavy oil accounts for a large share of global proven oil reserves and is thus a key energy resource. Yet its high viscosity and freezing point require complex, specialized processing. While chemical, microbial, and thermal recovery methods exist, a simple, controllable, and highly effective viscosity reduction method is still needed. Here, novel Fe₃O₄@SiO₂ nanoparticles capped with hexamethyldisilazane (HMDS) were synthesized as magnetic emulsifiers to reduce the viscosity of heavy oil. The as-synthesized Fe₃O₄@SiO₂-HMDS nanoparticles exhibit an average size of approximately 100 nm, along with good dispersion in oil and magnetic responsiveness. As emulsifiers, these nanoparticles promote the aquathermolysis reaction of extra-heavy crude oil at relatively low temperatures. Specifically, in our experiments, the amphiphilic emulsifier ME-8, with an SiO₂/HMDS molar ratio of 8:1, effectively reduced the apparent viscosity of three heavy oil samples (with initial viscosities of 27,500 cP, 58,000 cP, and 85,400 cP) by 67.27%, 68.96%, and 56.67%, respectively. These results were achieved under optimal conditions: an emulsifier mass fraction of 0.5%, a reaction temperature of 150\u0026deg;C, and a reaction time of 24 hours. This emulsifier-based method demonstrates promising potential for the exploitation of heavy crude oil.\u003c/p\u003e","manuscriptTitle":"Fe3O4 @SiO2 -hexamethyldisilazane amphiphilic magnetic emulsifier for viscosity-reduction of heavy oils via aquathermolysis reaction","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-11 13:34:18","doi":"10.21203/rs.3.rs-8769823/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-09T16:58:39+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-25T12:11:15+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-20T22:16:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-12T09:28:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"30314379343030950158829804470418880931","date":"2026-02-10T13:55:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"176938540306682866317052808947183311134","date":"2026-02-09T08:56:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"65744067241064568888171852629528625555","date":"2026-02-09T04:19:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"88597160924249428678037715206021090567","date":"2026-02-08T05:33:39+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-06T16:59:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"205474028342643434918746915458599771878","date":"2026-02-06T16:32:45+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-06T15:35:30+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-06T15:25:20+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-03T17:33:47+00:00","index":"","fulltext":""},{"type":"submitted","content":"Brazilian Journal of Chemical Engineering","date":"2026-02-03T01:36:52+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"brazilian-journal-of-chemical-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bjce","sideBox":"Learn more about [Brazilian Journal of Chemical Engineering](http://link.springer.com/journal/43153)","snPcode":"43153","submissionUrl":"https://www.editorialmanager.com/bjce/default2.aspx","title":"Brazilian Journal of Chemical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"355b426e-34b2-4ade-bd7c-ba507954af95","owner":[],"postedDate":"February 11th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-06T12:10:12+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-11 13:34:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8769823","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8769823","identity":"rs-8769823","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}