Liquid crystals transition temperatures

The correlation between molecular structure, liquid crystal transition temperatures and physical properties of the nematic phase of these materials of relevance to individual types LCDs is dealt with extensively in Chapter 3. 

Significant variations in the magnitude of the physical properties, such as the liquid crystal transition temperatures, viscosity, birefringence and the elastic and dielectric constants, of alkenyl-substituted compounds with a carbon-... 

The temperature of the hydration step should be above the gel-liquid crystal transition temperature of the lipid to allow the lipid to hydrate in its fluid phase with adequate agitation. Hydration time may differ slightly among lipid species and structures. We believe that good hydration prior to sonication makes the sizing process easier and improves the homogeneity of the preparation. 

T solid to nematic liquid crystal transition temperature... 

Tm), -A- liquid crystal-to-liquid crystal transition temperature and clearing temperature (T ) on spacer... 

The obtained polymer (Ma, 351 D) was confirmed to be the intended substance by infrared spectroscopy and nuclear magnetic-resonance spectroscopy and found to have a liquid crystal transition temperature of 135°C by thermal analysis. 

The membranes are prepared by vacuum filtration and stored at different temperatures. Salbutamol sulphate is used as a model drug across the COC-embedded membrane. It is evident that both manufacturing and store temperature significantly affect the characteristic of membranes. The thermally on-off switching membrane can be obtained by preparing the membranes above the liquid crystal transition temperature. 4 refs. 

The inclusion of cholesterol disturbs the crystalline structure of the gel phase, and the phospholipid chains are more mobile than in its absence. This prevents the crystallization of the hydrocarbon chains into the rigid crystalline gel phase. In the more fluid liquid crystalline phase, the rigid cholesterol molecules restrict the movement of the hydrocarbon chains. In consequence, the addition of cholesterol to lipid bilayers or lamellar mesophases gradually diminishes the gel-liquid crystal transition temperature and the enthalpy and broadens the DSC transition peak [72,73]. No transition can be detected by DSC at 50% cholesterol [73,74] (curve/of Fig. 7), which is the maximum concentration of cholesterol that can be incorporated before phase separation. However, laser Raman spectroscopic studies show that a noncooperative transition occurs over a very wide temperature range [75]. 

From here, a AF correction factor can be calculated that should be applied to all the temperatures measured in cooling runs. When this correction factor is calculated from several LC LC and LC I (where LC = liquid crystal) transition temperatures, it must be averaged to obtain an effective correction factor. 

Typically, the length ofa simulation varies between 1 and 10 ns. Even though such a simulation requires approximately 10 -10 time steps, it is not a sufficiently long time to collect complete, direct statistics about solute translocation. Thus, special techniques, described below, must be used to calculate both the distribution of a solute in the bilayer and the membrane permeability to a solute. The temperature of the system is usually held at a value in the 300-350 K range. Two considerations motivate the choice of the temperature. First, in some studies e.g., on anesthetic solutes) it is desired to simulate physiological conditions. Second, since the membrane permeability depends sensitively on the lipid phase, it is usually required that the bilayer be clearly above the gel-to-liquid-crystal transition temperature. 

The liquid-crystal transition between smectic-A and nematic for some systems is an AT transition. Depending on the value of the MacMillan ratio, the ratio of the temperature of the smectic-A-nematic transition to that of the nematic-isotropic transition (which is Ising), the behaviour of such systems varies continuously from a k-type transition to a tricritical one (see section A2.5.91. Garland and Nounesis [34] reviewed these systems in 1994. 

A liquid crystal compound in more cases Ilian not takes on more than one type of mesomorphic structure as the conditions of temperature or solvent are changed. In thermotropic liquid crystals, transitions between various... 

Recently, a molecular dynamics study of the phospholipid DLPE was reported by Damodaran et al. using a united atom model. The model was built from the crystal structure of DLPE reported by Elder et al. The fully hydrated DLPE bilayer has an interlamellar water layer of 5 A. The bilayer was solvated by 553 SPCE waters ( 11 water molecules/lipid) in the head group region. This lipid has a gel-to-liquid-crystalline transition temperature of... 

Transition-temperature determinations for liquid crystals have been the subject of numerous investigations 112-20). Not only can the melting points be determined, but also the liquid-crystal transitions. One of the first such determinations was that by Barrall ei al. (12) on anisaldazine, which is illustrated in Figure 7.41. A stable, linear heating rate is necessary because a rJC sudden departure for linearity can appear as a glass transition point on the DTA curve. The two curves in Figure 7.41 illustrate the use of temperature-axis amplification in order to separate closely spaced peaks. In... 

The coefficient of expansion is not very different in glassy and crystalline state. In the glassy state, the long ranged order of crystals does not occur-glasses are frozen-in liquids. The transition temperature depends on cooUng rate. 

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