{"paper_id":"3df2f926-1837-441e-9223-dd3af7b6fdf6","body_text":"License and Terms: This document is copyright 2020 the Author(s); licensee Beilstein-Institut.\nThis is an open access work under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0). Please note that the reuse,\nredistribution and reproduction in particular requires that the author(s) and source are credited and that individual graphics may be subject to special legal provisions.\nThe license is subject to the Beilstein Archives terms and conditions: https://www.beilstein-archives.org/xiv/terms.\nThe definitive version of this work can be found at https://doi.org/10.3762/bxiv.2020.140.v1\nThis open access document is posted as a preprint in the Beilstein Archives at https://doi.org/10.3762/bxiv.2020.140.v1 and is\nconsidered to be an early communication for feedback before peer review. Before citing this document, please check if a final,\npeer-reviewed version has been published.\nThis document is not formatted, has not undergone copyediting or typesetting, and may contain errors, unsubstantiated scientific\nclaims or preliminary data.\nPreprint Title High-throughput free surface electrospinning using solution\nreservoirs with different depths and its preparation mechanism study\nAuthors Jing Yin, Adnan Ahmed and Lan Xu\nPublication Date 10 Dez. 2020\nArticle Type Full Research Paper\nORCID® iDs Jing Yin - https://orcid.org/0000-0002-4645-9517; Adnan Ahmed -\nhttps://orcid.org/0000-0002-5095-7463; Lan Xu -\nhttps://orcid.org/0000-0003-2185-4104\n\n1 \nHigh-throughput free surface electrospinning using solution reservoirs \nwith different depths and its preparation mechanism study \nJing Yin, Adnan Ahmed, Lan Xu* \n \nNational Engineering Laboratory for Modern Silk, College of Textile and \nEngineering, Soochow University, 199 Ren-ai Road, Suzhou 215123, China \n*Corresponding author.  \nE-mails: 20184215040@stu.suda.edu.cn (J. Yin), adnanahmed0070@outlook.com (A. \nAhmed), lanxu@suda.edu.cn (L. Xu). \n1 Jing Yin and Adnan Ahmed contributed equally to this paper. \nAbstract \nThis paper presented a self-made spherical section free surface electrospinning \n(SSFSE) using solution reservoirs with different depths for obtaining high-throughput \nproduction of nanofibers , and studied its preparation mechanism . The effects of the \nsolution reservoir  depth on the SSFSE process a s well as  the quality and yield of \npolyacrylonitrile (PAN) nanofibers were investigated experimentally using high-speed \ncamera, precise electronic balance and scanning electron microscopy, and were \nanalyzed th eoretically by response surface methodology (RSM)  and numerical \nsimulation. The values predicted by the established RSM model and the electric field \nsimulation results obtained by Maxwell 3D were all consistent with the experimental \ndata, which showed that the solution reservoir depth had little effects on the quality of \nPAN nanofibers, but had great effects on the yields of them. When the maximum depth \nof solution reservoir was 4.29 mm, the PAN nanofibers prepared have the best quality \nand the highest yields.  \nKeywords: Free surface electrospinning ; Nanofibers; High-throughput production; \nResponse surface methodology; Electric field simulation \n \n1. Introduction \nDue to their characteristics of high specific surface area and aspect ratio, nanofibers \nare widely used in tissue engineering [1, 2], filtration [3], wound dressings [4], sound-\nabsorbing materials [5], food preservation [6] and so on. At present, the technologies \nfor preparing nanofibers ha ve self-assembly [7], phase separation [2], electrospinning \n(ES) [8-11], and so on. ES is one of the easiest ways to prepare nanofibers continuously. \nWith the increasing demand for nanofibers, more and more attention has been paid to \nthe high-throughput production of nanofibers. However, the yield of traditional single-\nneedle ES  (0.01-1g/h) is too low, which limits its commercial application  [12-14]. \nMulti-needle ES is considered as an effective method to increase the yield of nanofibers, \nbut it has some disadvantages, such as complicated design and  potential clogging [14, \n15]. Therefore, needleless ES  (NES) is presented to overcome the disadvantages of \nmulti-needle electrospinning and realize the high-throughput preparation of nanofibers \n[16]. NES usually means that the free surface of the spinning solution is subjected to \n\n2 \nfluctuations under the action of a high electric field, overcoming the surface tension of \nthe solution, forming many jets and then stretching into nanofibers [17]. In recent years \nmany types of needleless ES have been proposed for mass production of nanofibers , \nsuch as rotating shaft ES [18], free surface electrospinning (FSE) [19], bubble ES (BE) \n[20], and so on [21]. \nIn our previous researches [4, 22-26], a series of self-made NES devices for mass \nproduction of nanofibers have been developed and applied, such as modified MBE [22-\n24], sloping FSE (SFSE) [4], oblique section FSE (OSFSE) [25], spherical section FSE \n(SSFSE) [26]. According to these researches it was found that SSFSE was the optimal \nNES device for preparing nanofibers with the highest quality and yield. On this basis, \nthe SSFSE with a replaceable solution reservoir was designed to obtain high-throughput \nproduction of nanofibers, as shown in Fig.1, and the influence of the solution reservoir \nradius on the spinning effects of SSFSE was studied, which indicated the SSFSE device \nusing the solution reservoir with a radius of 25mm could  provide the highest quality \nand yield of nanofibers [26].   \n \nFigure 1: Schematic of the SSFSE device with a replaceable solution reservoir \nIn this paper, the influences of the solution reservoir depth on the spinning effects of \nSSFSE were investigated experimentally  by a combination of high -speed camera, \nprecise electronic ba lance and scanning electron microscopy . Response surface \nmethodology (RSM) involving central composite design (CCD) was applied to model \nand optimize the SSFSE process for evaluating the influence of spinning parameters on \nthe yield of polyacrylonitrile (PAN) nanofibers. And the preparation mechanism of the \nSSFSE device was studied by simulating the electric field distribution in the spinning \nprocess using Maxwell 3D. The RSM predicted values and the electric field simulation \nresults were all consistent wit h the experimental data, which showed that  the SSFSE \ndevice with different solution reservoir could produce nanofibers with higher quality \nand yield, and the solution reservoir depth had great effects on the yields of them. When \nthe maximum depth of solution reservoir was 4.29 mm, the highest quality and yield of \nPAN nanofibers were fabricated.  \n2. Materials and methods    \n2.1. Materials \n\n\n3 \nPolyacrylonitrile (PAN, Mw = 15w)  was obtained from Beijing Lark Branch Co., \nLtd. (Beijing, China). Sodium dodecylbenzene sulfonate (SDBS) was purchased from \nSinopharm Chemical Reagent Co. Ltd. (Shanghai, China) . N, N-dimethylformamide \n(DMF) was supplied from Shanghai Chemical Reagent Co., Ltd. (Shanghai, China).  \nFor obtaining the spinning solutions, 10% PAN and 1% SDBS were dissolved in DMF \nunder magnetic stirring at 60°C for 4h to get transparent liquid using a thermostatic \nmagnetic stirrer (DF-101S, Xinrui Instrument Factory, Changzhou, China). \n2.2. Apparatus \nThe replaceable solution reservoir of the SSFSE is made of a copper cylinder with a \nheight of 40mm and a diameter of 50mm. There are five solution reservoirs with \ndifferent maximum depths, which are obtained by truncating the copper cylinder using \nspheres with a radius of 45  mm, 55 mm, 65 mm, 75 mm and 85 mm respectively, as \nillustrated in Fig. 2. And the maximum depths (h), the areas of spherical section (S) and \nthe solution storage volumes (V) of the five solution reservoirs are calculated according \nto the different sphere radii (R), as shown in Table 1. \n \nFigure 2: Schematic diagram of the SSFSE solution reservoir truncated by a sphere. \n(a) is the 3D schematic diagram. (b) indicates the sphere which truncate the solution \nreservoir. (c) is the longitudinal cross-section view \n \nTable 1 The maximum depth (h), the area of spherical section (S), the solution storage \nvolume(V) of the solution reservoir obtained by different sphere radii \nR(mm) h (mm) S (mm2) V (mm3) \n45 7.58 2143.08 7673.36 \n55 6.01 2075.92 6010.73 \n65 5 2041 4974.19 \n75 4.29 2020.27 4250.08 \n85 3.76 2006.88 3718.82 \n \n2.3. Self-made SSFSE processes \nAccording to the reference [26], the SSFSE parameters were set as follows: the room \ntemperature was 20℃, the relative humidity was 70%, the receiving area was 200 mm \n× 200 mm, the receiving distance was 180 mm, and the applied voltages were 35 kV, \n40 kV and 45 kV. The spinning processes of the SSFSE solution reservoirs with \ndifferent depths were investigated by a high -speed camera (VRI Phantom -VEO-L, \nAmetek, California, USA),  and the initial voltage s of t hem were determined \n\n\n4 \nrespectively, as shown in Fig.3.  It could be seen that as the solution reservoir depth  \nincreased the initial voltage increased, due to the point discharge at the top edge of the \nreservoirs. And with the increase of the applied voltage, the number of jets on the \nsolution surface increased gradually. However, when the applied voltage was too high \n(45 kV), the jets became unstable and uneven. In addition, the decrease of the solution \nreservoir depth also enhanced the number of jets on the solution surface because of the \nhigher electric field intensity and more uniform electric field distribution . The \nexperiment results would be verified by simulating the electric field distribution in the \nSSFSE processes. \n    \nInitial voltage 25kV 35kV 40kV 45kV \n(a) SSFSE solution reservoir with a maximum depth of 7.58 mm \n    \nInitial voltage 26kV 35kV 40kV 45kV \n(b) SSFSE solution reservoir with a maximum depth of 6.01 mm \n    \nInitial voltage 28kV 35kV 40kV 45kV \n(c) SSFSE solution reservoir with a maximum depth of 5 mm \n    \nInitial voltage 30kV 35kV 40kV 45kV \n(d) SSFSE solution reservoir with a maximum depth of 4.29 mm \n    \nInitial voltage 32kV 35kV 40kV 45kV \n(e) SSFSE solution reservoir with a maximum depth of 3.76 mm \n\n\n5 \nFigure 3: Pictures of SSFSE processes of the solution reservoirs with different depths \nat different voltages \n2.4. Characterization \n2.4.1. Yield of nanofibers \nThe masses of PAN nanofibers prepared after spinning for 30 min were measured by \na precise electronic balance  (XJ120A, P recisa, Shanghai, China), and each of the \nmeasurements was repeated  five times to obtain the average value. Due to the same \narea of spinning surface, the calculation method of yield is as follows: \n𝑊 = (𝑊1 − 𝑊0) 𝑡⁄                          (1) \nwhere W is the yield of nanofibers, W0 and W1 are the masses of the aluminum foils \nbefore and after spinning respectively, and t is the spinning time. \n2.4.2. Morphology of nanofibers \nThe scanning electron microscopy (SEM, Hitachi S4800, Hitachi, Tokyo, Japan) was \nused to investigate the morphology of PAN nanofibers. And 10 SEM pictures and 100 \nnanofibers at random in each SEM picture of every sample were used to analyze the \ndiameter distribution of nanofibers by Image J software (National Institute of Mental  \nHealth, Bethesda, MD, USA). \n2.4.3. Response surface method and design of experiments \nThe r esponse surface method  (RSM) can be  applied to optimize and design \nexperiments, which  has the advantages of fewer experiments, higher accuracy and \nbetter predictable performance.  Central composite design (CCD)  as a standard RSM \ndesign can be used for modeling, analysis and optimization of electrospinning [26]. \nBecause the  solution reservoir  depth was determined by the radius of a sphere that \ntruncated the reservoir, two factors were two SSFSE parameters: the sphere radius and \napplied voltage, and the response was the yield of PAN nanofibers. The two factors and \nfactor levels were exhibited in Table 2. Based on CCD, an approximate mathematical \nrelationship between the response and the two factors (A: Sphere radius and B: voltage) \ncould be established by the following quadratic polynomial model [27, 28]: \nY = βo + β1A + β2B + β3A2 + β4B2 + β5AB             (2) \nwhere Y is the value of the yield of nanofibers, A is the value of the sphere radius, B is \nthe value of  the applied voltage, β0, β1, β2, β3, β4 and β5 are undetermined coefficients \nwhich can be estimated by experimental data. \nThe probability value (P-value) is presented to investigate the statistical significance \nof factors. P-values lower than 0.05 are considered as statistically meaningful values, \nwhich illustrate the factors have significant effects on the response [29]. R-squared (R2) \nis a n important indicator to indicate the statistical significance of the model , which \ndetermines how well the model agrees with the experimental results. \nTable 2 The factors and factor levels for experimental design \nFactors Factors levels \nA: Sphere radius (mm) 45, 55, 65, 75, 85 \nB: Applied voltage (kV) 35, 40, 45 \n2.4.4. Simulation of the electric field \nThe electric field distributions from the solution reservoir to the collector  in the  \nSSFSE processes with solution reservoirs of different depths were simulated using \nMaxwell 3D. The electric field simulations for these SSFSE processes were performed \nby the following experimental parameters: the copper reservoirs as positive poles were \ncylinders with a diameter of 50 mm and a height of 40 mm, which were truncated by \nspheres with a radius  of 45mm, 55mm, 65mm, 75mm and 85mm, respectively , t he \n\n6 \nelectric conductivity of copper was 5.8 × 10 11 μs/cm, the electric conductivity of PAN \nsolution was 2372 μs/cm, the applied voltage was 40 kV , and the distance from the \nsolution surface to the collector was 180 mm. \n3. Result and discussion \n3.1. Yield of PAN nanofibers \nFig.4 illustrated the yields of PAN nanofibers fabricated by the different SSFSE \ndevices at the different applied voltage. It could be found that with the increase of the \nvoltage the yield of PAN nanofibers obtained by the same SSFSE device increased, and \nwith the decrease of the solution reservoir depth the yield of nanofibers first increased \nand then decreased at the same voltage.  When the maximum depth of the solution \nreservoir was 3.76 mm at the applied voltages of 40 kV and  45 kV , the yields of \nnanofibers were all lower than those when the maximum depth of the solution reservoir \nwas 4.29 mm. This was because lots of jets were unstable and spread outward due to  \ntoo high electric field intensity, as indicated in Fig.3 (e). These outward expanding jets \nand too high spinning speed made it difficult for nanofibers to be collected on the \ncollector, leading to the decrease of the yield of nanofibers.  When the applied voltage \nwas 45 kV and the maximum depth of the solution reservoir was 4.29 mm, the yield of \nnanofibers reached a maximum of 27.34 g/h. The experiment results agreed with the \nobserved phenomena by a high-speed camera, which would be confirmed by RSM and \nelectric field simulation analysis . In addition, it was noticed that when the maximum \ndepths of the solution reservoirs  were 5 mm,  4.29 mm and 3.76 mm , the yield s of \nnanofibers prepared at 40 kV were similar to those at 45 kV. Considering the stability \nof the spinning process, the effect of the solution reservoir depth on the morphology of \nPAN nanofibers prepared at 40 kV would be investigated. \n \nFigure 4: Yield of PAN nanofibers prepared by different SSFSE solution reservoirs at \ndifferent voltages \n3.2. Morphology of nanofibers \nFig.5 showed the morphology of PAN nanofibers prepared by five SSFSE solution \nreservoirs with different depths at the voltage of 40 kV and the corresponding nanofiber \ndiameter distributions. Meanwhile, the average diameters and co nfidence intervals of \nthese nanofibers were indicated in Fig.5 (a-2,b-2,c-2,d-2,e-2). It could be seen that these \nPAN nanofibers were of good quality due to the good spinning effects of these SSFSE \n\n\n7 \nprocesses with five solution reservoirs of different depths. But as the solution reservoir \ndepth decreased, the average diameter of the prepared PAN nanofibers first increased \nand then decreased , and the uniformity of their diameter distributions all increased. \nWhen the maximum depth of the solution reservoir was 7.58 mm, the average diameter \nof the prepared nanofibers was smaller, but its diameter distributions was the most \nnonuniform due to the tip discharge generated by the sharpest top edge of the reservoir. \nWhen the maximum depth of the solution reservoir was 3.76 mm, the average diameter \nof nanofibers was the largest and its diameter distribution was mo st uniform because \ntoo fast spinning speed made the jet not fully stretched due to  the smallest reservoir \ndepth and the weakening of the tip discharge phenomenon. When the maximum depth \nof the solution reservoir was 4.29 mm, the average diameter of nanofibers was  \nminimum and its diameter distribution was more uniform. \n  \n(a) SSFSE solution reservoir with a maximum depth of 7.58 mm \n  \n(b) SSFSE solution reservoir with a maximum depth of 6.01 mm \n   \n(c) SSFSE solution reservoir with a maximum depth of 5 mm \na-1 \nb-1 \nc-1 \na-2 \nb-2 \nc-2 \n\n8 \n  \n(d) SSFSE solution reservoir with a maximum depth of 4.29 mm \n  \n(e) SSFSE solution reservoir with a maximum depth of 3.76 mm \nFigure 5: SEM pictures and the corresponding diameter distributions of PAN nanofiber \nprepared by the SSFSE solutions reservoirs with different depths  \n3.3. Response function \nThe effects of different  sphere radius (A) and applied voltage ( B) on the yield of \nPAN nanofibers were studied using the CCD technique. The 15 groups of experiments \ndesigned by the CCD method were shown in Table 3.  \nTable 3 Experimental design and response. \nRun Factors (actual values) Response (actual values) \nA: Sphere radius (mm) B: Voltage (kV) Yield (g/h) \n1 45 35 7.494 \n2 45 40 8.225 \n3 45 45 13.77 \n4 55 35 9.12 \n5 55 40 12.72 \n6 55 45 18.55 \n7 65 35 9.82 \n8 65 40 21.205 \n9 65 45 21.765 \n10 75 35 13.1775 \n11 75 40 26.80 \n12 75 45 27.34 \n13 85 35 15.808 \n14 85 40 25.91 \n15 85 45 26.96 \nTo obtain a quadratic polynomial equation and statistical analysis of the acquired \ndata, the analysis of variance (ANOVA) was performed according to Eq. (2), and P -\nd-1 \ne-1 \nd-2 \ne-2 \n\n9 \nvalues and R2 were determined [28], which were listed in Table 4. It indicated P-values \nfor the model and terms (A and B) were less than 0.05, which demonstrated the model \nand the two terms had significant influence on the response ( the yield of nanofibers ). \nR2 was 0.9208, which showed that the predicted value of the model agreed with the \nactual value. Therefore, the quadratic response surface model for the yield of nanofibers \ncould be expressed as the following equation:  \n          Y = 19.78 + 7.02A + 5.30B + 1.45A2 − 1.61B2 − 2.59AB        (3) \nAccording to Eq.  (3), the predicted yields of nanofibers were plotted, as shown in \nFig. 6. The actual values of yields of nanofibers were distributed along the predicted \ncurve, which indicated  the predicted values were in agreement with the experimental \ndata, illustrating that the model was suitable for the experimental data. \nTable 4 ANOVA for the quadratic regression model. \nSource Sum of \nsquares \nDegree of \nfreedom \nMean \nsquare F-value p-value Status \nModel 689.90 5 137.98 20.93 0.0001 Significant \nA-Radius 369..66 1 369.66 56.07 ＜0.0001 Significant \nB-Voltage 280.51 1 280.51 42.55 0.0001 Significant \nAB 10.49 1 10.49 1.59 0.2388 not Significant \nA2 6.84 1 6.84 1.04 0.3349 not Significant \nB2 22.39 1 22.39 3.40 0.0984 not Significant \nResidual 59.33 9 6.59 - - - \nTotal 749.23 14 - - - - \nR2 0.9208 - - - - - \n \n \nFigure 6: Predicted yields versus actual yields of electrospun PAN nanofibers \n  The relationship between the response and the factors can be visualized by the \ncontour and three-dimensional response surface plots. Fig. 7 exhibited the contour and \nthree-dimensional response surface plots of the yield of PAN nanofibers as a function \nof sphere radius  and applied voltage. It was obvious that when  the sphere radius \nremained constant, the yield of nanofibers increased with the increase of the voltage . \nAnd when the applied voltage kept constant, the yield of nanofibers increased first and \nthen decreased with the increase of the sphere radius. \n\n\n10 \n \nFigure 7: Contour (a) and three-dimensional (b) response surface plots of yield of \nPAN nanofiber as a function of sphere radius and applied voltage \n3.4. Simulating electric field \nIn order to study the preparation mechanism of the SSFSE device, Maxwell 3D was \nused to simulate the electric field distributions in the SSFSE processes  with solution \nreservoirs of different  depths, as shown in Fig. 8. More uniform electric field \ndistribution can help to produce finer and more uniform fiber [29]. Fig. 8 (a-1, b-1, c-\n1, d-1, e-1) represented the scalar plots of two -dimensional center section of the 3D \nelectric field simulations in these SSFSE processes and the according local magnified \nview of the reservoir top edge. It could be seen that the maximum electric field \nintensities all distributed at the top edge of the copper reservoir, making it easier to \nproduce jets. Fig.8 (a-3, b-3, c-3, d-3, e-3) showed the vector plots of the corresponding \nelectric field simulations in the same areas . It was found that the directions of the \nelectric fields were oriented directly towards to the collector  due to the cylindrical \nsymmetry of the solution reservoir and the cancellation of the vertical field components, \ncausing the jets to be subjected to the upward electric field force.  Fig. 8 (a-2, b-2, c-2, \nd-2, e-2) and Fig. 8 (a-4, b-4, c-4, d-4, e-4) exhibited the electric field distributions in \nthe axial (0 -180mm) direction and radial (0 -100mm) direction on the upper surface \ncenter of the five SSFSE reservoirs, respectively . It illustrated that the electric field \nintensities in the axial direction decreased as the distance from the solution surface \nincreased, and the electric field intensities in the radial direction first increased sharply, \nreached the maximum value at the top edge of the reservoir  because of the electron \ntransition from the solution to the copper, and then dropped sharply due to the electron \ntransition from the copper to the air. \n\n\n11 \n \n(a) SSFSE solution reservoir with a maximum depth of 7.58 mm \n \n(b) SSFSE solution reservoir with a maximum depth of 6.01 mm \n\n\n12 \n \n(c) SSFSE solution reservoir with a maximum depth of 5 mm \n \n(d) SSFSE solution reservoir with a maximum depth of 4.29 mm \n\n\n13 \n \n(e) SSFSE solution reservoir with a maximum depth of 3.76 mm \nFigure 8: Simulation of the electric field distributions in five SSFSE devices with \nsolution reservoirs of different depths at 40kV \nTo further compare the uniformity of electric field distributions of these five SSFSE \nprocesses, a parameter ƒ is introduced, which is calculated by the following formula \n[25]. The smaller its value, the more uniform the electric field distribution [25]. \n                           ƒ =\n𝐸max\n𝐸av\n                             (4) \nwhere Emax is the maximum electric field intensity and Eav is the average electric field \nintensity. \nThe calculated values of Emax, Eav and f in the radial (0 -20 mm more than the \ncorresponding radius) and axial (0-180 mm) directions of these five SSFSE processes \nwere displayed in Table 5, respectively. It could be seen that  as the solution reservoir \ndepth decreased the values of Emax and f in the radial directions all decreased, but the \nvalues of Eav in the radial directions as well as the values of Emax, Eav and f in the axial \ndirections all increased. When the maximum depth of the  solution reservoir was 7.58 \nmm, the values of Emax, Eav and f in the axial direction as well as Eav in the radial \ndirection were all minimum because of the deepest reservoir depth, but the values of \nEmax and f in the radial direction were maximum due to the tip discharge generated by \nthe sharpest top edge of the reservoir , leading to the most non -uniform electric field \ndistribution and relatively few jets  produced, as indicated in Fig. 3 (a). When the \nmaximum depth of the solution reservoir was 4.29 mm, the values of f in the axial and \nradial directions were relatively small er and the value of Eav was higher, which \ndemonstrated the electric field distribution was  more uniform and the electric field \nintensities were higher, leading to lots of uniform and stable jets  produced from the \nsolution surface, as exhibited in Fig. 3  (d), as well as  the nanof ibers obtained with \nhighest quality and yield, as shown in Fig. 5 (d) and Fig. 4. When the maximum depth \nof the solution reservoir was 3.76 mm, due to the smallest reservoir depth, the values \nof Emax, Eav and f in the axial direction as well as Eav in the radial direction were all \nmaximum, but the values of Emax and f in the radial direction were minimum, which \nmeant the electric field had the highest average intensity and the most uniform \ndistribution. This led to the formation of unstable and outward expanding jets  as well \nas too fast spinning speed , as illustrated in Fig. 3 (e), which made  it difficult for \nnanofibers to be fully stretched and collected, resulting in the nanofibers prepared with \nthe largest diameter and lower yield, as indicated in Fig. 5 (e) and Fig. 4. The analysis \n\n\n14 \nresults of the electric field distributions were consistent with the experimental results, \nas shown in Fig.3, Fig. 4 and Fig. 5. \nTable 5 The calculated values of Emax, Eav and f on the radial (0-20mm more than the \ncorresponding radius) and the axial  (0-180mm) directions of these five SSFSE \nprocesses. \nh \n(mm) \nEmax (V/m) Eav (V/m) f \nRadial Axial Radial Axial Radial Axial \n7.58 2.51×106 4.25×105 5.86×105 2.07×105 4.28 2.05 \n6.01 2.28×106 4.43×105 5.97×105 2.10×105 3.77 2.11 \n5 2.24×106 4.64×105 6.04×105 2.12×105 3.75 2.19 \n4.29 2.06×106 4.62×105 6.08×105 2.13×105 3.39 2.17 \n3.76 2.00×106 4.81×105 6.12×105 2.14×105 3.27 2.25 \n \n4. Conclusion  \nIn this paper, the effects of the solution reservoir depth on the SSFSE process as well \nas the quality and yield of  PAN nanofibers were investigated experimentally and \nanalyzed theoretically. The SSFSE process was observed by a high-speed camera, the \nmorphology and the y ield of PAN  nanofibers obtained  using the SSFSE were \ndetermined by a scanning electron microscopy (SEM) and a precise electronic balance, \nrespectively. According to the experimental data, a RSM model was established to  \noptimize the SSFSE process and evaluate the effect of the solution reservoir depth and \nthe applied voltage on the yield of nanofibers. The values predicted by RSM indicated \nthat the solution reservoir depth and the applied voltage all had great influences on the \nyield of nanofibers, which were consistent with the experimental results. Furthermore, \nthe numerical simulation of the electric field distribution by Maxwell 3D in the SSFSE \nprocess demonstrated the preparation mechanism of SSFSE, which illustrated that PAN \nnanofibers with the highest quality and yield c ould be obtained by the SSFSE device \nusing a solution reservoir with a maximum depth of 4.29 mm due to its higher average \nelectric field intensity and more uniform electric field distribution.  The simulation \nresults were verified by experimental data. \n \nAcknowledgments \nThe work is supported financially by National Natural Science Foundation of China \n(Grant No. 11672198), Jiangsu Higher Education Institutions of China  (Grant No. \n20KJA130001), Six Talent Peaks Project of Jiangsu Province (Grant No.GDZB -050), \nScience and Technology Guiding Project of China National Textile and Apparel \nCouncil (2020013), and PAPD (A Project Funded by the Priority Academic Program \nDevelopment of Jiangsu Higher Education Institutions). \n \nReferences \n1. Huerta, R. R.; Silva, E. K.; El-Bialy, T. Saldaña M. D. A.; Ultrason Sonochem. \n2019. \n2. Kang, J.; Hwang, J. Y.; Huh, M.; Yun, S. I. Macromol. Res. 2020. \n\n15 \n3. Avci, H.; Akkulak, E.; Gergeroglu, H.; Ghorbanpoor, H.; Uysal, O.; Sariboyaci, \nA.E.; Demir, B.; Soykan, M . N.; Pat, S .; Mohammadigharehbagh, R .; Ozel, C .; \nCabuk, A.; Guzel, F. D. J Appl. Polym. Sci. 2020, 137. \n4. Yin, J.; Xu, L. Int. J. Biol. 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