A New Twist on the Electroclinic Critical Point: Type I and Type II Smectic $C^*$ Systems
Abstract
This analysis of the electroclinic effect in ferroelectric liquid crystals with a first order Smectic---Smectic- (Sm---Sm-) transition, shows they can be either Type I or Type II. In temperature--field parameter space Type I systems exhibit a macroscopically achiral (in which the Sm- helical superstructure is expelled) low-tilt (LT) Sm---high-tilt (HT) Sm- critical point, which terminates a LT Sm---HT Sm- first order boundary. This boundary extends to an achiral-chiral triple point where the achiral LT Sm- and HT Sm- phases coexist with the chiral Sm- phase. In Type II systems the critical point, triple point, and first order boundary are replaced by a Sm- region, between LT and HT achiral Sm- phases, at low and high fields respectively. When the field is ramped up, the Type II system displays a reentrant Sm---Sm--Sm- phase sequence. A discontinuity in the tilt of the optical axis at each of the two phase transitions means the Type II system is tristable. The system is Type I or Type II depending on the ratio of two length scales, one is the zero-field Sm- helical pitch, the other depends on the latent heat at the zero-field first order Sm---Sm- transition. A system could be experimentally tuned by varying enantiomeric excess, between Type I and Type II behavior. We also show this Type I vs Type II behavior is the Ising universality class analog of Type I vs Type II behavior in XY universality class systems. Lastly, we make a complete mapping of the phase boundaries in temperature--field--enantiomeric excess parameter space (not just near the critical point) which shows a variety of interesting features, including a multicritical point, tricritical points and a doubly reentrant Sm---Sm--Sm---Sm- phase sequence.
Keywords
Cite
@article{arxiv.1902.05606,
title = {A New Twist on the Electroclinic Critical Point: Type I and Type II Smectic $C^*$ Systems},
author = {Josh Ziegler and Sean Echols and Matthew J. Moelter and Karl Saunders},
journal= {arXiv preprint arXiv:1902.05606},
year = {2019}
}
Comments
52 pages, 19 figures