Liquid crystalline state phase diagrams

Figure 16 shows a schematic diagram of phase transformations for rigid-chain polymers separated from isotropic solutions by introducing a nonsolvent into the system (this is a usual method of obtaining fibres and films) (cf. >). The initial isotropic solution with the polymer concentration V2 and the value of the Huggins-Flory parameter is in the monophase region. The critical concentration of the transition into liquid crystalline state for this system is v. When a nonsolvent is introduced, i.e. when x is increased up to the value >0.5 (x ), two routes of the phase transition... 

With respect to the structure of the anisotropic phase, the authors stated the liquid crystals were lamellar. They presented two pieces of evidence to support this contention. First, on the basis of the phase diagram for the dodecanol/SDS/water system, only two liquid crystalline stationary phases will exist (1) hexagonal, or... 

Mesophase A liquid crystalline state existing between the solid crystalline states and isotropic states of a compound homogeneous region in a phase diagram containing a self-assembled aggregate structure. 

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. 

The phase equilibrium in systems containing rigid-chain polymers is characterized by the formation of a liquid-crystalline state, which fact can be illustrated by the diagram due to Flory reproduced in Figure 3. At x values below 0,the polymer-solvent system forms either an isotropic (one-phase) solution mixture of... 

The effect of pressure and temperature on the phase diagram of P4MP1 was studied by Rastogi et al. [104], see Fig. 7. The polymer crystalline under ambient conditions becomes amorphous reversibly on increasing pressure in two widely separated temperature regimes (20°C and 200°C). The transformation occurs via a liquid crystalline state. The lower-... 

A complete classification of smectic phases by texture is not always possible. It can happen that similar textures are observed with two liquid crystalline states separated by a phase transition.If so, an extremely useful and powerful tool for assessing the type of mesophase is the determination of the isobaric temperature-concentration diagrams of binary mixtures. According to Sackmann and Demus isomorphous liquid crystals are considered as equivalent and characterized by the same symbol. While uninterrupted miscibility establishes isomorphism, the converse is not necessarily true. Temperature-composition phase diagrams for liquid crystalline mixtures can be generated from thermal data or, because of the various optical features characteristic of each mesophase structure, from observations of microscopic textures of the mesophases between crossed polarizers. The latter method (also called the contact method allows great rapidity in the assessment of the phase diagram. 

Fig. 4.14. Typical concentration-temperature phase diagram for rod-like polymers in concentrated solution. Poly(n-hexyl isocyanate) (PHIC) in toluene. L and L.C. indicate isotropic and liquid-crystalline states of solution, respectively. ...

The number of defects is maximal in the amorphous and liquid states. The phase diagram in Figure 5 shows the volume-temperature relationships of the liquid, the crystalline form, and the glass (vitreous state or amorphous form) [14], The energy-temperature and enthalpy-temperature relationships are qualitatively similar. 

The crystallization process can be illustrated by a phase diagram that shows which state (liquid, crystalline, or amorphous solid [precipitate]) is stable under a variety of crystallization parameters. It provides a means of quantifying the influence of the parameters such as the concentrations of protein, precipitant(s), additive(s), pH, and temperature on the production of crystals. Hence phase diagrams form the basis for the design of crystal growth conditions (McPherson, 1999 Ducruix and Giege, 1992 Ducruix and Giege, 1999 Chayen et ah, 1996 and references therein). 

Phase transition is an important property of membranes. Below the phase transition temperature, lipids are tilted and highly ordered. They are in their solid or "gel" state. Increasing the temperature leads to a pre-transition, characterized by periodic undulations and straightening of the hydrocarbon chain. Further increase of the temperature causes the main phase transition. Above the main phase transition temperature, lipids are fluid or "liquid crystalline." Figure 3 shows the phase diagram for the interaction of water with a lipid as well as its inferred arrangements in a model membrane (5). Phase transitions in membranes and membrane models have been extensively studied by spectroscopic techniques and by differential scanning calorimetry. 

In this connection let us consider a fragment of a schematic phase diagram in the region of high concentrations of a polymer capable of forming the liquid crystalUne phase (Fig. 2). In a crystalUne polymer containing no solvent (100% polymer, vf), the transition from the crystalline state (c) to the Uquid crystalline state (Ic) must take place at the temperature T -.ic and further transition into isotropic state (i), at the temperature Such transitions are called thermotropic, and the system formed at I, is called the thermotropic liquid crystal. The transition to the Uquid crystalline state can also occur by adding to a polymer a solvent at a temperature below T -. c-... 

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