Polymer blends containing liquid-crystalline components

Section 10.6 is dedicated to blends containing liquid-crystalline components. The mesophase behavior of liquid crystals (LCs) and liquid crystal polymers (LCPs), as well as the crystallization processes and the superstructure of blends of crystallizable polymers with LCPs and blends of LCPs, is described. 

When dealing with crystallizable miscible polymer blends containing a noncrystallizable component, some refinements had to be made. Some modifications were proposed by Alfonso and Russell (1986) and by Cimmino et al. (1989) for blends in which the amorphous component is segregated into the interlamellar region (see also Sect. 3.2.2.1). First, the chemical potential of the liquid phase might be altered by the specific interactions that are often responsible for the miscibility of polymers (Olabisi et al. 1979). Such interactions may change the free energy required to form a critical nucleus as well as the mobility of both the crystalline and amorphous components. Second, the noncrystallizable component has to... 

The free volume of thermoplastic miscible blends has also been determined as a function of blend composition (Zhou et al. 2003 Campbell et al. 1997 Roland and Ngai 1991). Those studies have shown that the degree of blend miscibility alters the free volume behavior as a function of blend composition. On the other hand, Hsieh et al. (2000) have studied a number of blends containing only thermotropic liquid crystalline polymers TLCP s as the only components. That work showed that regardless of their various miscibilities, TLCP blends tend to display smaller, fewer free volume sites than expected from a weighted average. This observation has been ascribed to the intrinsic affinity of nematic TLCP s. 

Using blends containing PCL, Koleske and Lundberg extended previous studies of polymer blends of wholly amorphous polymers to ones in which one component is crystalline [2]. An inherently crystallisable component may crystallise from a miscible amorphous blend, in a liquid-solid phase separation, and exhibit a melting transition close to that of the homopolymer normally the crystalline material would be a pure single polymer it is feasible that both components of a binary blend may crystallise separately. 

A comment needs to be added for the stress expression (eqn [19]). This expression assumes that the components in the blends are isotropic and no mobile emulsifier is included in the sharp interface so that the interfadal interartion can be represented by a single scalar constant, F. Equation [19] is to be modified if these assumptions are invalid. Namely, the interfadal interaction is to be represented in a tensorial form if the blend components are anisotropic (such as liquid crystalline molecules), and a strain- and time-dependent contribution is to be added in eqn [19] if the blend contains mobile emulsifiers. Furthermore, a general expression of o is to be utilized instead of eqn [19] if the interface is diffuse (which is the case for weakly segregated blends such as those near the phase-separation point). Nevertheless, eqn [19] is applicable to a large fraction of polymer blends utilized in industry, and the description given later is limited to such blends. 

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