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تسجيل مستخدم جديدThe Biaxial Smectic-A* Phase -- A New Phase, Already But Unknowingly Discovered?
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Karl Saunders
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The biaxial smectic-A* (Sm-A_B*) phase, appearing in the phase sequence Sm-A*--Sm-A*_B--Sm-C*, is analyzed using Landau theory. It is found to possess a helical superstructure with a pitch that is significantly shorter than the pitch of the Sm-C* helical superstructure. The Sm-A_B*--Sm-C* transition can be either 1st or 2nd order, and correspondingly there will be either a jump or continuous variation in the pitch. The behaviors of the birefringence and electroclinic effect are analyzed and found to be similar to those of a Sm-C*_alpha phase. As such, it is possible that the Sm-A_B* phase could be misidentified as a Sm-C*alpha phase. Ways to distinguish the two phases are discussed.
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Leiming Chen (College of Science
, The China University of Mining andn Technology
, Xuzhou
2011
We study the smectic $A$-$C$ phase transition in biaxial disordered environments, e.g. fully anisotropic aerogel. We find that both the $A$ and $C$ phases belong to the universality class of the XY Bragg glass, and therefore have quasi-long-ranged tr
anslational smectic order. The phase transition itself belongs to a new universality class, which we study using an $epsilon=7/2-d$ expansion. We find a stable fixed point, which implies a continuous transition, the critical exponents of which we calculate.
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We study theoretically the smectic A to C phase transition in isotropic disordered environments. Surprisingly, we find that, as in the clean smectic A to C phase transition, smectic layer fluctuations do not affect the nature of the transition, in sp
ite of the fact that they are much stronger in the presence of the disorder. As a result, we find that the universality class of the transition is that of the Random field XY model (RFXY).
We develop a theory of Smectic A - Smectic C phase transition with anomalously weak smectic layer contraction. We construct a phenomenological description of this transition by generalizing the Chen-Lubensky model. Using a mean-field molecular model,
we demonstrate that a relatively simple interaction potential suffices to describe the transition. The theoretical results are in excellent agreement with experimental data.
A high-resolution calorimetric study has been carried out on nano-colloidal dispersions of aerosils in the liquid crystal 4-textit{n}-pentylphenylthiol-4-textit{n}-octyloxybenzoate ($bar{8}$S5) as a function of aerosil concentration and temperature s
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