Crystallization isotropic

The variation of the transition temperatures of these polybibenzoates with the number of methylene units in the spacer is shown in the lower part of Fig. 5. Melting temperatures, Tm, (crystal-isotropic melt transition) are obtained [9] for m > 7 and m = 3 (monotropic behavior), while for the other members, Tm really represents the... 

The hydrotropic action of a dicarboxylic acid is discussed against the general features of hydro-tropic action the liquid crystal/isotropic solution equilibrium. It is shown that the hydrotropic action of the dicarboxylic acid in question, 8-[5(6)-carboxy-4-hexyl-cyclohex-2-enyl] octanoic acid, depends on its conformation at an interface. 

The second group involves polymers with three-dimensional ordering of side branches (e.g., those forming Mj-phaseXTable 5). On X-ray patterns of these polymers 3-4 narrow reflexes at wide angles are observed. As a rule, the authors define this type of structure as crystalline, or ascribe a smectic type of structure, characteristic for ordered smectics in SE or SH phases. The heats of transition from anisotropic state to isotropic melt are usually small and do not exceed the heats of transition smectic liquid crystal — isotropic melt . The similarity of structural parameters of three-dimensionally ordered smectics and that of crystalline polymers of the type here considered, make their correct identification quite a difficult task. 

The polymers of 284 are hydrogels and can take up a moderate amount of water. The ROMP of 285 only proceeds to completion if the polystyrene side chains are kept reasonably short (n = 4, 7 or 9). Polymers of monomers such as 286 exhibit a nematic or smectic mesophase resulting from side-chain crystallization. Isotropization temperatures increase with increasing MW, becoming constant at about 30-50 repeat units. Side-chain crystallization tends to be suppressed as the MW increases. 

Fig. 31. Illustration of some possible thermodynamic relationships between crystal, isotropic, and liquid-crystal phases.

Figure 4. Crystal-isotropic (k-i), crystal-nematic (k-n), and nematic-isotropic (n-i) transition temperatures as a function of mole fraction of -(Cl ) q- spacer pertaining to the series of MBPE-8,10 copolyethers, containing methylbiphenyl ethane mesogen and randomly distributed -(CH,)0- and -(CH,).n- spacers (adapted from ref. 15).

There are various types of molecular orientations possible in the surfactant film. The surfactant molecules may be in the form of crystals, isotropic gels or one or more of several different types of mesophases (33). The techniques which may be used to study the molecular orientations inside these surfactant films have been reviewed by Singer (34). 

The areas bounded by the curves represent the conditions for the stable existence of the four single phases, solid crystals, liquid crystals, isotropic liquid, and vapour. 

In this modified Flory model, the liquid crystal-isotropic transition of rods in a solution occurs at... 

A liquid-solid phase diagram established for blends of iPP/POE by means of DSC and LS is presented at the top left of Fig. 7.12, displaying four distinct regions isotropic (I), coexistence of crystal-isotropic (Ci +1), coexistence of crystal-crystal-isotropic (C1+C2 + I), and crystal-crystal (Ci + C2- -C3). Cj and C2 represent the a- and y-form crystals of iPP, respectively, while C3 is designated for POE crystals (31). The blend preparation is identical to the procedure conducted for sPP/POE blend specimens. These iPP/POE blends are found to be completely miscible in the melt state, showing little or no depression of the melting point with composition. 

Figure 7.12 (a) Solid-liquid phase diagram for the iPP/POE blends displaying isotropic (I), coexistence of crystal-isotropic (Cj -f 1), two crystals form—isotropic (Cj + C2 +1) regions, and crystal-crystal (Ci+ C2 + Cj) (Cl and C2 correspond to a- and -y-forms of iPP and C3 corresponds to crystal of POE), obtained by means of LS and DSC. (b-f) Optical micrographs displaying the dependence of supercooling on crystalline structure in the blend of iPP/POE (10/90) isothermally crystallized at various indicated temperatures. 

Table I. Liquid Crystal/Isotropic Liquid Transition Temperatures...

Table 1 Thermal pressure coefficients y, transition volumes A 7, and volume-dependent transition entropies ASy of n-alkanes and polyoxyethylene (POE) for the crystal-isotropic (Cl) phase transitions conformational entropy changes estimated by the rotational isomeric state approximation are included for comparison...

This may be demonstrated by extruding two identical pieces of pure, high molecular weight PHB homopolymer lace from the melt into air at ambient conditions using, for example, a simple MFI grader. If one piece is left to crystallize isotropically as a control, while the other is stretched immediately by 50-100%, then the latter will remain elastic for several minutes after the former has fully crystallized. Both samples, however, eventually harden to the same isotropically crystalline and very brittle condition. 

Fig. 7. Schematic representation of a liquid crystal-isotropic phase diagram for rigid rods in solution.

So far, the role of phase separation in gelation has been limited to polymers which are regarded as flexible in solution. Thermoreversible gels can be formed from solutions of many rod-like polymers. " Miller et have reviewed the phase separation and networks formed by some rod-like polymers. The nature of the restoring force in such networks of rods must clearly be different from that of a rubber-like, flexible polymer network. However, that network formation occurs via a phase separation remains a possibility. Flory has developed a detailed theory for the liquid crystal-isotropic phase behaviour of rod-like particles in a diluent. 

Wee EL, Miller WG (1971) Liquid crystal-isotropic phase equilibriums in the system poly (y-benzyl a-L-glutamate)-methylformamide. J Phys Chem 75 1446-1452... 

Arguments for the minimal model system being the traveling cholesteric liquid crystal-isotropic liquid phase boundary are given in this section. The sample is prepared so that the length scale imposed on it by the non-equilibrium driving forces is comparable to the cholesteric liquid crystal s equilibrium length, its pitch. In a pattern formation context, knows time ... 

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