Transition hexatic-liquid

In the smectic B phase, the molecules within the layers are aligned perpendicularly to the layers, but the molecules of the Sp and Si phases within layers are tilted with respect to the layer normal by a tilt angle. The azimuthal of the tilt direction or the projections onto the smectic layers of the Sp and Si phases are different. In the former, the projections of molecules onto the layer point to the edge of the hexatic, while in the latter, to the apex. The difference seems not so significant, but Sp and Si liquid crystals are not miscible, and there is a phase transition between them when the temperature varies. 

Depending on a material, single smectic monolayers can exist in two different modificati(His, liquid-like and hexatic like. Properties of these monolayers are shown in Table 5.1. Upon melting, a two-dimensional hexatic layer undergoes the transition into the liquid-like layer. It is spectacular that hexatic layers like liquid layers do not support the in-plane shear [14]. The layer can be sheared by as small force (stress) as is wished. 

Free suspended films of smectic liquid crystals can show a change in the crystalline order from the quasi-two-dimensional to the three-dimensional one [11]. Very thin smectic B films (number of monolayers n < 10) are two dimensional with the hexatic in-plane order, and with (low temperatures) or without (higher temperatures) a tilt of molecules. With increasing n (n > 20) the transition to various three-dimensional crystalline structures is observed. 

To test the theoretically predicted thermal properties [37,38] related to the two-dimensional liquid-hexatic transition critically, we have carefully characterized the hexatic B phase in compound 54COOBC [30] and found that it does not display herringbone order. To make a clear distinction between these two cases, we propose to use hexatic B to denote the phase found in 54COOBC and use SmB for the phase found in the nmOBC compounds which has a clear indication of some degree of herringbone order. 

Using Monte-Carlo simulations, we have investigated the role of herringbone order on the liquid-hexatic transition of nmOBC [42]. Based on the coupled XY Hamilton-... 

As the hexatic to liquid transition is approached, is renormalized by the topological defects, in a way that may depend on t Therefore, it is not clear how to compare the... 

The study of stacked hexatics has yielded a complete classification of the large variety of thermotropic liquid crystal phases. It has also presented a single experiment which yields a simultaneous measurement of many crossover anisotropy exponents, previously obtained from separate complex experiments. It is also an excellent system to reveal dimensional crossover and the interplay between two- and three-dimensional physics. For very thin layers, the stacked hexatic layers can be used to extract the hexatic stiffness, or Frank constant, and thus test predictions of defect mediated transition theories. 

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