High resolution x-ray study of nematic-smectic-A and Smectic-A-reentrant nematic transitions in liquid crystal+aerosil gels

TL;DR

This study investigates how aerosil nanoparticle gels affect phase transitions in liquid crystal mixtures, revealing that reentrant characteristics remain stable while smectic order weakens with increased 6OCB concentration.

Contribution

It provides high-resolution x-ray diffraction analysis of disorder effects on nematic-smectic and reentrant nematic transitions in liquid crystals with aerosil gels, highlighting the stability of reentrant features.

Findings

Reentrant characteristics are largely unaffected by aerosil gels.

Short-range smectic order weakens with increased 6OCB concentration.

High- and low-temperature nematic phases are similar in structure.

Abstract

We have studied the effects of quenched random disorder created by dispersed aerosil nanoparticle gels on the nematic to smectic-A (N-SmA) and smectic-A to reentrant nematic (SmA- RN) phase transitions of thermotropic liquid crystal mixtures of 6OCB (hexyloxycyanobiphenyl) and 8OCB (octyloxycyanobiphenyl). These effects are probed using high-resolution synchrotron x-ray diffraction techniques. We find that the reentrant characteristics of the system are largely unchanged by the presence of the aerosil gel network. By comparing measurements of the smectic static structure amplitude for this 8OCB-6OCB+aerosil system with those for butyloxybenzilidene-octylaniline (4O.8)+aerosil gels, we find that the short-range smectic order in the smectic-A phase is significantly weaker in the reentrant system. This result is consistent with the behavior seen in pure 8OCB-6OCB mixtures. The strength of the smectic ordering decreases progressively as the 6OCB concentration is increased. Detailed line shape analysis shows that the high- and low-temperature nematic phases (N and RN) are similar to each other.