The Impact of Nanoparticles on the Previtreous Behavior: Glass-Forming Nematogenic E7 Mixture-Based Nanocolloids

The report discusses the impact of nanoparticles on the previtreous behavior of glass-forming systems. The presented studies were carried out via broadband dielectric spectroscopy (BDS) in nanocolloids composed of nematogenic liquid crystalline (LC) mixture E7 and paraelectric BaTiO3 nanoparticles. Tests started in the isotropic liquid phase, showing critical-like dielectric constant changes associated with prenematic fluctuations and weakly discontinuous isotropic–nematic phase transition. Subsequently, evolutions of the dielectric constant, two primary relaxation times (related to  τ and α τ' processes), and DC electric conductivity are considered in the nematic phase, down to the glass temperature Tg. The prevalence of the portrayal via the ‘double exponential’ MYEGA equation is shown for dynamic properties. Monitoring of the dielectric constant revealed the exogenic impact of nanoparticles, leading to the permanent arrangement of rod-like LC molecules. For the primary loss curve, critical-like changes of its maximum (peak) are evidenced: peak''∝1T-Tg* for Tg<T<Tg+25K, where Tg*<Tg is the extrapolated singular temperature. Such behavior is shown for both pure E7 and nanocolloids. The heuristic model commenting on this unique behavior is presented. It recalls a hypothetical link between the glass transition and a hidden near-critical phase transition, avoiding a symmetry change.