Phase transition-molecular weight relationship

EXAMPLES PHASE TRANSITIONS-MOLECULAR WEIGHT RELATIONSHIP... 

However, a PS-fo-PI/PI blend shows direct L G transitions without appearance of the PL phase. The L microdomain is more favourable than the PL phase since the volume fraction of the PI block component and the symmetry of microdomains is increased by the addition of PI homopolymer. Hence, the PL phase may not be formed as an intermediate structure if relatively high molecular weight PI homopolymer is added. The latter is not able to effectively fill the corners of the Wigner-Seitz cells in consequence packing frustration cannot be released and the PL phase is not favoured [152]. In contrast, the addition of low molecular weight PI homopolymer to the minor component of the PL phase reduces the packing frustration imposed on the block copolymers and stabilizes it [153]. Hence, transition from the PL to the G phase indicates an epitaxial relationship between the two structures, while the direct transition between L and G yields a polydomain structure indicative of epitaxial mismatches in domain orientations [152]. 

It has been the merit of Picken (1989, 1990) having modified the Maier-Saupe mean field theory successfully for application to LCPs. He derived the stability of the nematic mesophase from an anisotropic potential, thereby making use of a coupling constant that determines the strength of the orientation potential. He also incorporated influences of concentration and molecular weight in the Maier-Saupe model. Moreover, he used Ciferri s equation to take into account the temperature dependence of the persistence length. In this way he found a relationship between clearing temperature (i.e. the temperature of transition from the nematic to the isotropic phase) and concentration ... 

The system styrene-acrylonitrile copolymer (SAN) 28% acrylonitrile/ poly (methyl methacrylate) exhibits thermodynamic solubility relationships adequate for studying phase transition phenomena. The molecular weight properties of the polymers used in this study (Table III) were measured by gel permeation chromatography. The cloud-point curve for binary mixtures of these two polymers was determined by a technique developed previously (10). 

Macleod s relation provides a number of important relationships for analyzing the effects of molecular weight, glass transition, phase transition (crystallization), and chemical constitution on surface tension, as discussed below. 

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