Phase behavior of polymers

A number of theoretical models have been proposed to describe the phase behavior of polymer—supercritical fluid systems, eg, the SAET and LEHB equations of state, and mean-field lattice gas models (67—69). Many examples of polymer—supercritical fluid systems are discussed ia the Hterature (1,3). 

Kammer, H. W., Kressler, H. and Kummerioewe, C Phase Behavior of Polymer Blends - Effects of Thermodynamics and Rheology. Vol. 106, pp, 31-86. 

Phase Behavior of Polymer Blends Volume Editor Freed, K. 

The high-pressure phase behavior of polymer-solvent-supercritical carbon dioxide systems was investigated experimentally The polymers used were poly(methyl methacrylate), polystyrene, polybutadiene, and poly(vinyl ethyl ether) at concentrations ranging from 5 to 10% in mixtures with toluene or tetrahydrofuran. The experiments were conducted for temperatures from 25 to 70°C and pressures up to 2200 psi in a high-pressure cell (Kiamos and Donohue, 1994). 

Table 3. Phase behavior of polymers having the same mesogenic group linked to the different main chains (AT = extent of the nematic phase)...

Vaia, R. A., Liu, W., and Koemer, H. Analysis of small-angle scattering of suspensions of organically modified montmorillonite Implications to phase behavior of polymer nanocomposites, J. Polym. Sci. B.Polym. Phys. (2003), 41, 3214-3236. 

Of course, nanocomposites are not the only area where mesoscale theories are being used to predict nanostructure and morphology. Other applications include—but are not limited to—block copolymer-based materials, surfactant and lipid liquid crystalline phases, micro-encapsulation of drugs and other actives, and phase behavior of polymer blends and solutions. In all these areas, mesoscale models are utilized to describe—qualitatively and often semi-quantitatively—how the structure of each component and the overall formulation influence the formation of the nanoscale morphology. 

Balazs, A. C., Ginzburg, V. V., Lyatskaya, Y., Singh, C., and Zhulina, E., Modeling the phase behavior of polymer-clay nanocomposites, in "Polymer-Clay Nanocomposites" (T. Pinnavaia, and G. Beall, Eds.), Wiley, Chichester, UK (2000). 

This article reviews the phase behavior of polymer blends with special emphasis on blends of random copolymers. Thermodynamic issues are considered and then experimental results on miscibility and phase separation are summarized. Section 3 deals with characteristic features of both the liquid-liquid phase separation process and the reverse phenomenon of phase dissolution in blends. This also involves morphology control by definite phase decomposition. In Sect. 4 attention will be focused on flow-induced phase changes in polymer blends. Experimental results and theoretical approaches are outlined. 

The phase behavior of polymer blends comprising amorphous polymers is experimentally well accessible in a window which is bounded at high temperatures by the thermal decomposition temperature of the polymer components and at low temperatures by the glass transition temperature of the system (cf. Fig. 1). Below the glass transition temperature the phase behavior can be estimated only tentatively. 

Finally, a challenging problem is to discuss the influence of hydrodynamic flow fields on the phase behavior of polymer blends. This is of fundamental interest and of technological importance as well since stresses and corresponding deformations are encountered during processing of blends. Extension of studies to blend systems under external flow is necessary for the better understanding of structure formation in polymer blends outside equilibrium. 

The first is to develop thermodynamic issues to understand the complex phase behavior of polymer blends. Experimental determination of miscibility regions provides the individual segmental interaction parameters necessary for predictions of various phase equilibria. 

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