Melting point, liquid crystals

Table 3.1-5 Melting points and heats of fusion for isomeric [BMIM][PFg] and [PMIM][PFs] ionic liquids, showing melting point and crystal stability increasing with the degree of branching in the alkyl substituent.

NMR cryoporometry relies on the melting point depression, i.e., the difference in the melting point of crystals with a finite size d, Tm(d), relative to the value of the bulk liquid Tm, which is given by the simplified Gibbs-Thomson equation [16] ... 

Stannic Chloride Pentahydrate. Stannic chloride pentahydrate [10026-06-9] is a white, crystalline, deliquescent solid that is soluble in water or methanol and stable at 19—56°C. It is used in place of the anhydrous chloride where anhydrous conditions are not mandatory. It is easier to handle than the fuming anhydrous liquid form. The pentahydrate is prepared by dissolving stannic chloride in hot water, thereby forming the pentahydrate at a temperature above the melting point and crystallizing by cooling. The cake is broken into small lumps for packaging. 

Processes are now available to provide controlled release to liquid pesticides, molten lower melting point pesticides, and solid higher melting point pesticide crystals in the size range and volume demanded of pesticide products. These processes will continue to develop into more robust and simpler systems. New processes wiU be developed. 

The vapor pressure of liquid iodine at its freezing point, 114° C, is 90 mm Hg. This is exactly the same as the vapor pressure of the crystals at this temperature, as described in the section before the preceding one. That is, iodine gas at a pressure of 90 mm Hg is in equilibrium with the liquid at 114° C, the freezing point of the liquid, and this gas is also in equilibrium with iodine crystals at this temperature, their melting point. The crystals and the liquid are in equi librium at the freezing point (melting point), and they then have exactly the same vapor pressure. If the two phases had different vapor pressures the phase with the larger vapor pressure would continue to evaporate, and the vapor would continue to condense at the other phase, until the first phase had disappeared. 

Phenol has a low melting point, it crystallizes in colourless prisms and has a characteristic, slightly pungent odor. In the molten state, it is a clear, colourless, mobile liquid. In the temperature range T < 68.4 °C, its miscibility with water is limited above this temperature it is completely miscible. The melting and sohdification points of phenol are quite substantially lowered by water. A mixture of phenol and ca 10% water is called phenolum liquefactum, because it is actually a liquid at room temperature. Phenol is readily soluble in most organic solvents (aromatic hydrocarbons, alcohols, ketones, ethers, acids, halo-genated hydrocarbons etc.) and somewhat less soluble in aliphatic hydrocarbons. Phenol forms azeotropic mixtures with water and other substances. 

Subcooling means that a liquid (or melt) can be cooled below its melting point without crystallization. It is one of the main reasorrs to add a suitoble rmcleating agent. 

Other alcohols from the Augusta facility include some production of ALCHEM 123 and 145 and ISALCHEM 123 and 145 alcohols. These alcohols are obtained from freeze fractionation of some of the LIAL 123 and LIAL 145 alcohols. This process is similar to the one practiced in the fats and oils industry called winterization. The neat alcohol is cooled with or without a solvent. The linear terminal alcohols have fairly high melting points and crystallize from the liquid. 

The best known of the chiral liquid crystal phases is the cholesteric phase or chiral nematic (N ). Here an asterisk is used to indicate a chiral phase. The cholesteric phase (Figure 2.10) was the first liquid crystal to be discovered by Reinitzer in 1888. Reinitzer observed pure cholesterol benzoate under the microscope and noticed two apparent melting points solid crystal to the phase that is now known as cholesteric and then a second melting point to the isotropic liquid phase. Cholesterol is a chiral molecule. 

From considerations similar to those outlined above in the section on nucleation it is expected that considerable superheating above the melting point would be required for the homogeneous nucleation of melting in a crystal. Such nucleation has, however, not yet been observed. When a crystal is heated above its melting point liquid is invariably observed to form at the free surfaces at negligible departures from equilibrium. The melting process... 

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