Soft versus hard confinement effects on the phase transitions, and intra- and inter-molecular dynamics of 6BT liquid crystal constrained in electrospun polymer fibers and in nanopores

This work examines the behavior of a liquid crystal (LC) under soft confinement, resulting from interactions between polymer and guest liquid crystalline molecules, and under hard confinement, imposed by rigid pore walls. It studies the confinement effects for electrospun fibers composed of poly(epsilon-caprolactone) (PCL) and different weight content of 4-hexyl-4'-isothiocyanatobiphenyl (6BT) liquid crystal, and 6BT enclosed in nanoporous alumina, with pore diameters of 200 nm, 120 nm, 80 nm and 40 nm. Differential scanning calorimetry, broadband dielectric and Fourier-transform infrared spectroscopy were employed to gain detailed insights into the effects of both forms of confinement on 6BT. The crystallization process of 6BT was found to be enhanced in the composite fibers, but fully suppressed for the material confined in pores. The relaxation rates of the rotational motion of the LC molecules around their short axis in the 25.6 wt% 6BT and 17 wt% 6BT PCL/6BT fibers are in line with those found for 6BT in the 200 nm and 80 nm pores. Two-dimensional correlation spectroscopy (2D-COS) analysis of infrared spectra confirmed that soft and hard confinement have different impacts on the intramolecular dynamics of 6BT. The study also discusses the influence of guest molecules on the intramolecular potentials of PCL. (C) 2021 Elsevier B.V. All rights reserved.