Fractional volume changes, phase transitions

Table 2. Fractional volume changes (in %, upper right) and related information (lower left) for phase transitions in mesophases of chiral compounds.

Yamada et al. [9,10] demonstrated that the copolymers were ferroelectric over a wide range of molar composition and that, at room temperature, they could be poled with an electric field much more readily than the PVF2 homopolymer. The main points highlighting the ferroelectric character of these materials can be summarized as follows (a) At a certain temperature, that depends on the copolymer composition, they present a solid-solid crystal phase transition. The crystalline lattice spacings change steeply near the transition point, (b) The relationship between the electric susceptibility e and temperature fits well the Curie-Weiss equation, (c) The remanent polarization of the poled samples reduces to zero at the transition temperature (Curie temperature, Tc). (d) The volume fraction of ferroelectric crystals is directly proportional to the remanent polarization, (e) The critical behavior for the dielectric relaxation is observed at Tc. 

We note that earlier research focused on the similarities of defect interaction and their motion in block copolymers and thermotropic nematics or smectics [181, 182], Thermotropic liquid crystals, however, are one-component homogeneous systems and are characterized by a non-conserved orientational order parameter. In contrast, in block copolymers the local concentration difference between two components is essentially conserved. In this respect, the microphase-separated structures in block copolymers are anticipated to have close similarities to lyotropic systems, which are composed of a polar medium (water) and a non-polar medium (surfactant structure). The phases of the lyotropic systems (such as lamella, cylinder, or micellar phases) are determined by the surfactant concentration. Similarly to lyotropic phases, the morphology in block copolymers is ascertained by the volume fraction of the components and their interaction. Therefore, in lyotropic systems and in block copolymers, the dynamics and annihilation of structural defects require a change in the local concentration difference between components as well as a change in the orientational order. Consequently, if single defect transformations could be monitored in real time and space, block copolymers could be considered as suitable model systems for studying transport mechanisms and phase transitions in 2D fluid materials such as membranes [183], lyotropic liquid crystals [184], and microemulsions [185],... 

This transition by which molecules self-assemble forming crystals is referred to as crystallization [2, 3]. In this case a discontinuous change in the specific volume is expected (Fig. 21.1). A classical experimental approach to characterize the nature of the crystals and the overall fraction of crystalhne phase mainly involves scattering and diffraction measurements [4]. Precise... 

Polymer phase transitions are traditionally probed by exploiting the temperature dependence of x to induce segregation. The location of the transition can be readily changed by adjusting the component volume fractions, ( > or N. Recently the effects of liquid organic solvents , homopolymer diluents and pressure have been studied in efforts to assess the phase behavior of blends and copolymers under realistic processing conditions. 

The measurement is based on the observation of phase transitions in fluid mixture of known mole fraction composition xi. In a closed system with the possibility to change (or measure) the volume V, the temperature T and the pressure P are recorded in the state when the number of phases changes, namely when the first liquid drop appears in the homogeneous vapor phase ( dew point ) or when the first vapor bubble appears in the... 

The normalized optical density variation as a function of the temperature of linear and microgel poly(NIPAM) is illustrated in Figure 9.23. The optical density increases with increasing the temperature for both linear thermally sensitive polymer and microgel particles. Such behavior is related to change in the refractive index of the polymer (ep. In fact, below the volume phase transition temperature, the polymer is highly hydrated (i.e., e + (1 4>)6p, O is the water fraction in... 

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