Thermotropic polymer phase transitions

Other cases, polymers can undergo lyotropic or thermotropic liquid crystalline phase transitions, which can often be observed and recorded in a polarized light microscope. 

Large numbers of functionalized LB films have been prepared. Highly ordered LB films have been formed by the inclusion of surface-active cobaltous phthalocyanine [168] amphiphilic TCNQ was assembled to function as conducting LB films [169] liquid-crystalline LB films, potentially capable of undergoing thermotropic or lyotropic phase transitions [170, 171], have also been generated. Spacer groups introduced into polymeric surfactants (23) helped to stabilize the LB films which they formed by decoupling the motion of pendant polymers (see Fig. 13) [172]. 

Both polymer melts and polymer solutions sometimes form phases with orientational and positional ordci. Thermotropic polymer liquid crystals possess at least one liquid crystal phase between the glass-transition temperature and the transition temperature to the isotropic liquid. Lyotropic polymer liquid crystals possess at least one liquid cry stal phase for certain ranges of concentration and temperature. 

The isotropic-to-nematic transition is determined by the condition [1 — (2/3)TBBWBB/k T] = 0 whereas the spinodal line is obtained when the denominator of XAA is equal to zero. These conditions are evaluated in the thermodynamic limit (Q = 0) in Fig. 7 for a Maier-Saupe interaction parameter Web/I bT = 0.4xAb and for NA = 200, N = 800, vA = vB = 1. When the volume fraction of component A(a) is low, the isotropic-to-nematic phase transition is reached first whereas at high < >A the spinodal line is reached first. In the second case, the macromolecules do not have a chance to orient themselves before the spinodal line is reached. This RPA approach is a generalization of the Doi et al. [36-38] results (that were developed for lyotropic polymer liquid crystals) to describe thermotropic polymer mixtures. Both approaches cannot, however,... 

In contrast to that, the short fluorinated side groups of poly-XIII did not lead to thermotropic LC phases, but resulted in microphase-separated block copolymers caused by the hydrophobic and oleophobic character of fluorinated polymers. This interpretation was supported by DSC data, which gave the thermal transitions for both blocks. 

Liquid crystals (LCs) are described as a fluid phase that flows like a liquid and is oriented in a crystalline manner. LCs are divided into two types thermotropic LCs, where the LC phase transition is dependent on temperature or lyotropic LCs, where the LC phase transition occurs as a function of solvent concentration. To introduce liquid crystallinity to conjugated polymers, LC moieties can be introduced to the polymer side chains for side chain-type liquid crystallinity. On the other hand, designing conjugated polymers with rigid main chain structures with flexible alkyl side chains for solubility enables main chain-type liquid crystallinity. 

George, E., Porter, R. (1988). Depression of the Crystalnematic Phase Transition in Thermotropic Liquid Crystal Copolyesters. J. Polym. Sci., 26(1), 83-90. 

STRUCTURE-PROPERTY RELATIONS IN FLEXIBLE THERMOTROPIC MESOPHASE POLYMERS I. PHASE TRANSITIONS IN POLYESTERS BASED ON THE AZOXYBENZENE MESOGEN... 

The large body of thermotropic liquid crystalline polymers is polyesters [14], some of which have been successfully commercialized. And very recently, quite a lot of thermotropic liquid crystalline polyimides have been reported [15]. In this chapter, the crystallization behavior and phase transition kinetics of thermotropic polyesters and polyimides will be discussed. 

Effect of Polymers on Thermotropic Phase Behavior. In order to determine if the polymers had any direct effect on the bilayers, the gel-to-liquid crystalline phase transition temperature was measured for the samples. The gel-to-liquid crystalline phase transition temperature has been found to be a very sensitive measure of bilayer packing and order. If the polymers were directly interacting with the bilayer, it should be observed in the transition temperature and enthalpy. 

Some thermotropic polymer systems switch at a certain temperature reversibly between a highly transparent and a light scattering state. Such an optical effect can be caused either by a phase transition between an isotropic and an anisotropic (liquid crystalline) state or by a phase separation process. Two different classes of thermotropic polymer materials have been extensively studied in recent years polymer blends and polymer gels. 

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