Molecular dynamics of a short range ordered smectic phase nanoconfined into porous silicon

TL;DR

This study investigates the molecular dynamics of 8CB liquid confined in porous silicon, revealing a gradual slowdown and glass-like behavior due to confinement, culminating in crystallization at low temperatures.

Contribution

First detailed investigation of molecular dynamics of 8CB in porous silicon using quasielastic neutron scattering, highlighting confinement effects on phase behavior.

Findings

Significant reduction in molecular dynamics due to confinement.

Continuous glass-like slowdown of dynamics with cooling.

Crystallization occurs in two steps at low temperature.

Abstract

4-n-octyl-4-cyanobiphenyl (8CB) has been recently shown to display an unusual sequence of phases when confined into porous silicon (PSi). The gradual increase of oriented short-range smectic (SRS) correlations in place of a phase transition has been interpreted as a consequence of the anisotropic quenched disorder induced by confinement in PSi. Combining two quasielastic neutron scattering experiments with complementary energy resolutions, we present the first investigation of the individual molecular dynamics of this system. A large reduction of the molecular dynamics is observed in the confined liquid phase, as a direct consequence of the dynamical boundary conditions imposed by the confinement. Temperature fixed window scans (FWS) reveal a continuous 'glass-like' reduction of the molecular dynamics of the confined liquid and SRS phases on cooling down to 250 K, where a solid-like behavior is finally reached by a two steps crystallization process.