Phases thermotropic

Licjuid Crystals. Ferroelectric Hquid crystals have been appHed to LCD (Uquid crystal display) because of their quick response (239). Ferroelectric Hquid crystals have chiral components in their molecules, some of which are derived from amino acids (240). Concentrated solutions (10—30%) of a-helix poly(amino acid)s show a lyotropic cholesteric Hquid crystalline phase, and poly(glutamic acid ester) films display a thermotropic phase (241). Their practical appHcations have not been deterrnined. 

Comparison ot Tables V and VI demonstrates that the thermal behavior of MelOCOO-PPO and MelOCOO-PECH are very similar, with the glass transition temperatures converging with substitution. Therefore, it appears that when very long spacers are used with the same mesogen, the polymer backbone has little effect on the thermotropic phases formed. This conclusion is supported by additional unpublished experiments performed in our laboratory. 

Kostecka-Gugala, A., D. Latowski, and K. Strzalka. 2003. Thermotropic phase behaviour of alpha-dipalm-itoylphosphatidylchohne multibilayers is influenced to various extents by carotenoids containing different structural features—evidence from differential scanning calorimetry. Biochim. Biophys. Acta 1609 193-202. 

Sujak, A., K. Strzalka, and W.I. Gruszecki. 2007b. Thermotropic phase behaviour of lipid bilayers containing carotenoid pigment canthaxanthin A differential scanning calorimetry study. Chem. Phys. Lipids 145 1-12. 

Liquid crystalline phases1 can be divided into two classes thermotropic phases are obtained by temperature variations and exist in a limited temperature interval (see Figure 7.1) lyotropic phases are instead formed by mixing two or more substances, for example, water and amphiphilic compounds or polymers and a solvent. Especially for amphiphilic compounds in water, temperature may play a role in determining the phase behavior. 

Figure 7.1 Illustration of different aggregation states obtained (from left to right) by increasing temperature crystal (K), smectic C (SmC), nematic (N) and isotropic (I). Row a shows macroscopic appearance of samples in row b, short-range microscopic ordering is represented (each bar represents a molecule) thermotropic phase diagram of row c illustrates relevant transition temperatures (Tm melting temperature Tsmc-N transition temperature between SmC and N Tc clearing temperature) row d shows different texture of different states as seen through polarizing microscope (with crossed polars, isotropic phase appears black).

Rozycka-Roszak, B., Pruchnik, H. and Kaminski, E. (2000). The effect of some phenyltin compounds on the thermotropic phase behaviour and the structure of model membranes, Appl. Organomet. Chem., 14, 465 -72. 

Papahajopoulos, D., M. Moscarello, E.H. Eylar, and T. Isac. 1975. Effects of proteins on thermotropic phase transitions of phospholipid membranes. Biochim Biophys Acta 401 317-335. 

Besides these thermotropic phase transitions, a variety of pressure-induced phase transformations can be observed," and it has been demonstrated that temperature and pressure have non-congruent effects on the structural and phase behaviour of these systems. 

Thermotropic phases are those that occur in a certain temperature range. If the temperature is raised too high, thermal motion will destroy the delicate cooperative ordering of the LC phase, pushing the material into a conventional isotropic liquid phase. At too low a temperature, most LC materials will form a conventional (though anisotropic) crystal. Many thermotropic LCs exhibit a variety of phases as the temperature is changed. For instance, a particular mesogen may exhibit various smectic and nematic (and finally isotropic) phases as temperature is increased. 

The aggregates created by amphiphiles are usually spherical (as in the case of micelles), but may also be disc-like (bicelles), rodlike, or biaxial (all three micelle axes are distinct) (Zana, 2008). These anisotropic self-assembled nanostructures can then order themselves in much the same way as liquid crystals do, forming large-scale versions of all the thermotropic phases (such as a nematic phase of rod-shaped micelles). 

This statistical theory includes contributions from an attractive intermolecular potential. The anisotropic attraction stabilizes the parallel alignment of neighboring molecules, and the theory then considers a mean-field average of the interaction. Solved self-consistently, this theory predicts thermotropic phase transitions consistent with the experiment. 

Hays LM, et al. Antifreeze glycoproteins inhibit leakage from liposomes during thermotropic phase transitions. Proc Natl Acad Sci USA 1996 93 6835-6840. 

The influence of cholesterol concentration at various temperatures on the thermotropic phase behavior and organization of saturated PE bilayers has been studied by combining DSC, FT-IR, and 31P-NMR. It was found that incorporation of low levels of cholesterol into the bilayer caused a progressive reduction in the temperature, enthalpy, and overall cooperativity of the lipid hydrocarbon chain melting transition... 

Brandenburg, K., Blume, A. Investigations into the thermotropic phase behaviour of natural membranes extracted from Gram-negative bacteria and artificial membrane systems made from lipopolysaccharides and free lipid A. Thermochim Acta 119 (1987) 127-142. 

Krill, S. L., Knutson, K. and Higuchi, W. I. The stratum comeum lipid thermotropic phase behavior. Biochimica et Biophysica Acta 7772(2) 281-286, 1992. Golden, G. M. et al. Lipid thermotropic transitions in human stratum comeum. Journal of Investigative Dermatology 86 255-259, 1986. 

Thermotropic Phases. Figure lisa representation of the temperature of the Isotropic-cholesteric transition in the case of hydroxypropylcellulose (HPC) and fully acetylated acetoxypropylcellulose (APC) (15). The range of molecular weights Is rather large In the case of HPC, It extends from low masses (2000) to very high ones (1,000,000). Two main features appear ... 

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