Liquid crystalline polymers phase diagrams

Figure 6 shows the phase diagrams plotting temperature T vs c for PHIC-toluene systems with different Mw or N [64], indicating c( and cA to be insensitive to T, as is generally the case with lyotropic polymer liquid crystal systems. This feature reflects that the phase equilibrium behavior in such systems is mainly governed by the hard-core repulsion of the polymers. The weak temperature dependence in Fig. 6 may be associated with the temperature variation of chain stiffness [64]. We assume in the following theoretical treatment that liquid crystalline polymer chains in solution interact only by hardcore repulsion. The isotropic-liquid crystal phase equilibrium in such a solution is then the balance between S and Sor, as explained in the last part of Sect. 2.2. 

Because biopolymers may have properties uncommon in synthetic systems, they can be very attractive as model systems to test specific ideas. An early example of this can be seen in the work on PBLG, a synthetic polypeptide. Although the motivation for its original synthesis failed, it provided a firm basis for many of the early studies on lyotropic liquid crystalline polymers. It was one of the first systems to have its phase diagram characterised, for comparison with Flory s predictions, and a study of its viscosity demonstrated that there is a non-monotonic increase in viscosity with concentration as the liquid crystalline phase is entered. 

FIGURE 11.11 Schematic diagram of (a) the nematic phase and (b) the smectic phase for main-chain liquid crystalline polymers, showing the director as the arrow. The relative ordering is the same for side-chain polymer liquid crystals. 

In summary, NMR studies can deal with a wide range of problems in surfactant science. These include, e.g., molecular transport, phase diagrams, phase structure, self-association, micelle size and shape, counterion binding and hydration, solubilization, and polymer-micelle interactions. NMR is fruitfully applied to isotropic or liquid crystalline bulk phases, to dispersions (vesicles, emulsions, etc.), to polymer-surfactant mixtures, and to surfactant molecules at solid surfaces. In all cases NMR can provide information on molecular interactions and dynamics as well as on microstructure. 

In SMPs with a liquid crystalline transition the specific heat capacity increases significantly up to the transition point due to long range fluctuations of the order parameter near the transition [49]. At the transition temperature, a first-order phase transition occurs. The recorded DSC peak of the liquid crystalline transition will be the mixture of these two contributions. A schematic example for a liquid crystalline polymer is shown in Fig. 2 (diagram e), showing transitions in the form of sharp endothermic peaks, Tc-n for the crystal-nematic transition and for the nematic-isotropic transition. 

Physical changes and measurements. These include melting, crystalline phase changes, ehanges in liquid and liquid crystalline states and in polymers, phase diagrams, heat capacity, glass transitions (Tg), thermal conductivity, difftisivity, emissivity, etc. 

Figure 6. Diagrammatic representation of the phase diagram of a rodlike liquid crystalline polymer in solution.

FIGURE 1.13. The phase diagram and molecular structure of the liquid crystalline polymers. Transition temperatures are in °C. 

Figure 6.30 Phase transitions in thermotropic liquid-crystalline polymers. The isotropization temperature (Tj) is shown in the diagram.

The X-ray difFraction patterns shown in Fig. 6.47 were obtained for a liquid-crystalline polymer at four different temperatures in order of increasing temperature. Make phase assignments and draw a phase diagram. 

Matkar et al. have hypothesized what would happen to crystalline blend phase diagrams if one relaxes the last assumption of the Floty diluent theory of crystalline polymer solutions, namely, the complete rejection of polymeric solvent from the crystalline phase [66, 67]. In addition, Xu et al. have developed a new theory for a binary crystalline polymer blends based on a combination of liquid-liquid phase separation and solid-liquid phase transition by taking into consideration the coupling interaction between the solid crystal and amorphous liquid phase [71]. 

If there are included among the diluents mixed with the crystalline polymer some which are sufficiently poor solvents, the phase diagram may then exhibit liquid-liquid phase separation, in addition to the liquid-crystal boundary curve. Examples are shown in Figs. 133... 

In the dynamic Monte Carlo simulations described earlier, we used a crystalline template to suppress supercooling (Sect. A.3). If this template is not present, there will be a kinetic interplay between polymer crystallization and liquid-liquid demixing during simulations of a cooling run. In this context, it is of particular interest to know how the crystallization process is affected by the vicinity of a region in the phase diagram where liquid-liquid demixing can occur. 

FIGURE 7.32. Phase diagram of PMOXA-b-PDMS-b-PMOXA in water and Cryo-TEM image of the lamellar phase formed at x = 50. x = polymer fraction in water in % w/w La = lamellar liquid crystalline phase. 

Liquid-crystalline solutions and melts of cellulosic polymers are often colored due to the selective reflection of visible fight, originating from the cholesteric helical periodicity. As a typical example, hydroxypropyl cellulose (HPC) is known to exhibit this optical property in aqueous solutions at polymer concentrations of 50-70 wt%. The aqueous solution system is also known to show an LCST-type of phase diagram and therefore becomes turbid at an elevated temperature [184]. 

It is interesting to note, however, that a polymer foam of sufficient durability could be produced even at high surfactant concentrations if, for example, a formulation of polymerising surfactant such as sodium co-acrylamidoundecanate or oleic alcohol is used [134]. This can be realised only in the region of the phase diagram corresponding to the existence of a lamellar liquid-crystalline structure. 

This article deals with some topics of the statistical physics of liquid-crystalline phase in the solutions of stiff chain macromolecules. These topics include the problem of the phase diagram for the liquid-crystalline transition in die solutions of completely stiff macromolecules (rigid rods) conditions of formation of the liquid-crystalline phase in the solutions ofsemiflexible macromolecules possibility of the intramolecular liquid-crystalline ordering in semiflexible macromolecules structure of intramolecular liquid crystals and dependence of die properties of the liquid-crystalline phase on the microstructure of the polymer chain. 

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