Critical Behavior of a Noncritical Field: Destruction of Smectic Order at the Smectic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>A</mml:mi><mml:mtext>−</mml:mtext><mml:mi>C</mml:mi></mml:mrow></mml:math>Tricritical Point and Implications for de Vries Behavior

We conduct an in-depth analysis of the electroclinic effect in chiral, ferroelectric liquid crystal systems that have a first order Smectic-A *-Smectic-C * (Sm-A *-Sm-C *) transition, and show that such systems can be either Type I or Type II. In temperature-field parameter space Type I systems exhibit a macroscopically achiral (in which the Sm-C * M helical superstructure is expelled) low-tilt (LT) Sm-C * U-high-tilt (HT) Sm-C * U critical point, which terminates a LT Sm-C * U-HT Sm-* CU first order boundary. Notationally, Sm-C * M /Sm-C * U denote the Sm-C * phase with/without a modulated superstructure. This boundary extends to an achiral-chiral triple point at which the macroscopically achiral LT Sm-C * U and HT Sm-C * U phases coexist along with the chiral Sm-C * M phase. In Type II systems the critical point, triple point, and first order boundary are replaced by a Sm-C * M region, sandwiched between LT and HT Sm-C * U phases, at low and high fields respectively. Correspondingly, as the field is ramped up, the Type II system will display a reentrant Sm-C * U-Sm-C * M-Sm-C * U phase sequence. Moreover, discontinuity in the tilt of the optical axis at each of the two phase transitions means the Type II system is tristable, in contrast to the bistable nature of the LT Sm-C * U-HT Sm-C * U transition in Type I systems. Whether the system is Type I or Type II is determined by the ratio of two length scales, one of which is the zero-field Sm-C * helical pitch. The other length scale depends on the size of the discontinuity (and thus the latent heat) at the zero-field first order Sm-A *-Sm-C * transition. We note that this Type I vs Type II behavior in this ferroelectric smectic 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 all regions of temperature-fieldenantiomeric excess parameter space (not just near the critical point) and show that a variety of interesting features are possible, including a multicritical point, tricritical points and a doubly reentrant Sm-C * U-Sm-C * M-Sm-C * U-Sm-C * M phase sequence.

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Critical Behavior of a Noncritical Field: Destruction of Smectic Order at the SmecticA−CTricritical Point and Implications for de Vries Behavior

Cited by 2 publications

References 20 publications

Layer contraction of smectic liquid crystals and the compensation model

Layer contraction of smectic liquid crystals and the compensation model

Type-I and type-II smectic-C*systems: A twist on the electroclinic critical point

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