Reduced Glass Transition Temperature with Preserved Super-Arrhenius Dynamics in Nanoconfined Glass-Forming Nematic

Abstract

The molecular dynamics and glass-forming behavior of 4-cyano-3-fluorophenyl 4-butylbenzoate (4CFPB) liquid crystal was investigated by broadband dielectric spectroscopy in anodic aluminum oxide cylindrical nanopores of 35 and 73 nm diameter. The primary $α$-relaxation was analyzed using the Vogel-Fulcher-Tammann (VFT) and Mauro-Yue-Ellison-Gupta-Allan (MYEGA) models. Confinement reduces the glass transition temperature from 217 K in bulk to 208-210 K, while preserving the super-Arrhenius character of the $α$-relaxation and a fragility index of approximately 60. Unlike in previously studied 6 and 8 nm pores, the secondary $β$-relaxation remains detectable, with possible intramolecular contributions examined by density functional theory calculations. Next to the pore-size-dependent changes in molecular dynamics and glass transition temperature, cold crystallization is not observed. These findings highlight the distinct effects of geometrical confinement on molecular relaxation, glass formation, and crystallization kinetics.