Phase transition, liquid crystal

Frenkel D 1992 Computer simulations of phase transitions in liquid crystals Phase Transitions in Liquid Crystals ed S Martellucci and A N Chester (New York Plenum)... 

The results of differential scanning calorimetry(DSC) indicate the change in aggregation state. The trans micelle showed a main endothermic peak at 14 2°C(A H =1.0 kcal/mol), corresponding to a gel-liquid crystal phase transition, whereas the transition temperature for the cis micelle appeared at 11.9°C( AH = 0.8 kcal/mol). This is unequivocal evidence that the trans-cis photoisomerization is a sufficient perturbation to alter the state of molecular aggregation. 

The parameters of the JT distortions were calculated by the X -method for a series of crystals in good agreement with experimental melting temperatures [14]. The details of the theory and specific calculations seemingly require additional refinements, but the main idea of the JT origin of the liquid-crystal phase transition seems to be quite reasonable. This work thus makes an important next step toward a better understanding of the relation between the macroscopic property of SB and the microscopic electronic structure, the JT effect parameters. 

The gel to liquid crystal phase transition temperature of DHPC bilayers containing 5-oxo KSA or 12-oxo KSA, at the concentrations used here, is around 46 C (data not shown). 

DHPC l -dihexadecyl-sn-glycero-3-phosphocholine KSA potassium stearate 5-oxo KSA 5-oxo potassium stearate 12-oxo KSA 12-oxo potassium stearate 9HP 9-heptadecanone Tc temperature of the gel-to-liquid crystal phase transition of DHPC bilayers 43.41C... 

The rate and character of the molecular motions of both the molecules embedded in the lipid bilayer and lipid molecules themselves are strongly dependent on the temperature [19, 203], At a certain temperature tm, the gel-liquid crystal phase transition is known to occur for the membrane made of a synthetic lipid. For example, tm = 41.5 °C for the membranes from DPL. In the vesicles formed by a mixture of lipids, e.g. egg lecithin, the phase transition occurs smoothly rather than jumpwise and starts below 0 °C. Note that the permeability of lipid membranes increases notably upon transition from the liquid crystal state to the gel state [204]. 

Subsequent studies illustrated the complexity of the phase transitions in di-alkyl polysilanes and the dramatic effects these have on the optical and conductive properties. A general conclusion that could be reached was that the mobility of charge invariably decreases in going from the crystal to the liquid crystal phase, and if subsequent higher temperature liquid crystal phase transitions occur, these result... 

Lekkerkerker H N W, Buining P, Buitenhuis J, Vroege G J and Stroobants A 1995 Liquid crystal phase transitions in dispersions of rodlike colloidal particles Observation, Prediction and Simulation of Phase Transitions In Complex Fluids ed M Baus, L F Rull and J P Hansen (Dordrecht Kluwer) pp 53-112... 

Only near liquid to liquid-crystal phase transitions should this argument be inapplicable. 

The DSC thermogram of the liposome-embedded heme was measured to estimate the phase transition of the lipid bilayer of the liposome-embedded heme . The DMPC-liposome showed the endothermic peak at 24 °C, which was corresponding to the gel-liquid crystal phase transition temperature (T,) of the liposome . But for the liposome in which a simple heme such as I was embedded, the phase transition peak was broadened and shifted to lower temperature (22 °C). On the other hand, the peak was also observed at 24 °C for the DMPC liposome/lipid-heme. This suggests that the orientation of the phospholipid in the liposome is equivalent for the DMPC-liposome and the DMPC liposome/lipid-heme and that the compatibility of the lipid-heme with the phospholipid is large enough to form a stable liposome. 

Figure 9. NMR spectra of the plasma membranes of Acholeplasma laidlawii enriched in palmitic acid labeled at the 13-position (I3-Ai 16 0) and in oleic acid labeled at the 12-position (12-d2 18 1). Spectra were obtained at the growth temperature, 37°C. The temperatures of optimal growth, To, and the calorimetric gel to liquid crystal phase transition of the lipids in the membranes, T, are indicated. Details of sample preparation and spectral acquisition are given in Ref. 23 and 24.

H.N.W. Lekkerkerker, G.J. Vroege, Liquid crystal phase transitions in suspensions of mineral colloids new life from old roots. Phil. Trans. R. Soc. A 371, 20120263 (2013)... 

Table 11.1 Liquid crystal phase transition temperatures of Poly-1...

W.M. Gelbart and B. Barboy, A van der Waals picture of the isotropic-nematic liquid crystal phase transition, Accts. Chem. Res. 13(8), 290-296, (1980). doi 10.1021/ar50152a007... 

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