Thennotropic liquid crystals

Thennotropic liquid crystal phases are fonned by anisotropic molecules witli long-range orientational order and in many types of stmcture witli some degree of translational order. The main types of mesogen are Arose tlrat are rodlike or calamitic and Arose Arat are disclike or discotic. 

Thennotropic liquid crystal phases are fonned by rodlike or disclike molecules. However, in the following we consider orientational ordering of rodlike molecules for definiteness, although the same parameters can be used for discotics. In a liquid crystal phase, the anisotropic molecules tend to point along the same direction. This is known as the director, which is a unit vector denoted n. 

Recent Advances in the Rheology of Thennotropic Liquid Crystal Polymers... 

Lyotropic liquid crystals are those which occur on the addition of a solvent to a substance, or on increasing the substance concentration in the solvent. There are examples of cellulose derivatives that are both thennotropic and lyotropic. However, cellulose and most cellulose derivatives form lyotropic mesophases. They usually have a characteristic "critical concentration" or "A point" where the molecules first begin to orient into the anisotropic phase which coexists with the isotropic phase. The anisotropic or ordered phase increases relative to the isotropic phase as the solution concentration is increased in a concentration range termed the "biphasic region." At the "B point" concentration the solution is wholly anisotropic. These A and B points are usually determined optically. 

Thennotropic and lyotropic liquid crystals share a common state of matter with many analogies in their structural and physical properties. However, these two fields of liquid crystal research are usually treated completely separately. This is partially due to historical reasons, but also to striking differences in some aspects of these two classes of liquid crystals. One of these differences is the occurrence of thermotropic phases which do not have a lyotropic counterpart A compelling example of this is the thermotropic ferroelectric SmC phase. Due to its unique chirality effects, i.e. ferroelectricity and a helical configuration of the tilt-direction, this phase attracted considerable scientific interest over the last decades. However, there are no reports found in literature about a SmC analog phase in lyotropic liquid crystals. 

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