Glassy liquid crystals stable

Figure 6, Representative morphologically stable glassy liquid crystals.

A dithienylethene-based liquid crystal material has been synthesized. This provides a morphologically stable, photoresponsive glassy nematic system in which the refractive index and optical birefringence can be modulated by photochemical means (Equation 7) <2004CSR85>. 

In the 1930 s it was shown by E. Vorlander [Trans. Faraday Soc., 29, 907 (1933)] that some liquid crystals could be quick frozen to a metastable brittle glassy state. By working with a polymeric molecule, a synthetic polypeptide called poly-y-benzyl-L-glutamate, we have been able to obtain stable solid films with a liquid crystalline local structure. These films can be obtained in conditions describable as rubbery, leathery, or glassy, as is common for polymer films. The unusual local structure of the molecules in the liquid crystalline phase gives rise to magnetic and optical properties heretofore not obtainable with polymeric systems. 

Similar to the other liquid crystal polymers described in Section 11.16, these materials offer the possibiUty of locking the chiral nematic phase into the glassy state by rapid supercooUng to temperatures below T. This leads to a preservation of the structure and, of course, the reflected color, thereby leading to the formation of stable, lightfast, monochromatic films, when suitable systems are used. 

L. Wolf and K. Ristau1 observed that colourless phosphorus can be obtained pure only in a darkened room, in the absence of oxygen and moisture. It is best obtained in an atm. of nitrogen either by fractional distillation, or by fractional crystallization. It is either a colourless, transparent, glassy mass, or it is white and finely crystalline. It melts to a clear, colourless liquid. It is stable under the above-named conditions, but rapidly becomes yellow in light. 

Fig. 5. Temperature dependence of the entropy difference between various supercooled liquids and their stable crystals, A5. is the entropy change upon melting, and is the melting temperature. (Reprinted with permission from W. Kauzmann. The nature of the glassy state and the behavior of liquids at low temperatures. Chem. Rev. (1948) 43 219. Copyright 1948, American Chemical Society.)...

Sometimes (18) the water molecules that fail to freeze on lowering the temperature are denoted as bound. This notion is open to criticism, however. It is true that collagen shares with other polymers the property that a considerable fraction of water remains unfrozen on lowering the temperature. On the basis of the number of grams of water per g of polymer the values are 0.5, 0.3 and 0.3 for collagen, elastin, and methyl-cellulose, respectively. For different reasons the polymer chains are essentially immobile. For collagen the crystalline, rodlike, molecules are apparently in close contact with each other and in elastin and methylcellulose the amorphous polymers are in the glassy state. At temperatures below 0 C ice is the stable phase in bulk. In the narrow, fixed, polymer interstices, however, space requirements are insufficient to form three-dimensional ice crystals. Other options available to the water molecules are to remain in the interstices in liquid form, or to form ice outside the polymer as a separate phase. 

Figure 1. Schematic phase diagram of noncrystalline water. Liquid water is stable above the melting temperature line 7m (/). Below this temperature and above the homogeneous nucleation temperature 7h F) liquid water is metastable (supercooled). The no man s land is the region where crystallization cannot be avoided experimentally. Glassy water exists below the crystallization temperature 7x F) T (F) is the glass transition temperature above which glassy water becomes an ul-traviscous liquid. For glassy water at 1 bar, 7 136K it is not clear yet what the...

This chromophore has a very low tendency to crystallize. After melting (102°C) on cooling the liquid phase, no crystallization occurs, and the amorphous liquid phase is stable at room temperature over days in a glassy state (Tg = 37 C). Glassy amorphous films can be easily obtained by spin coating from DMF solution, and... 

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