Spinodal decomposition, tests

Thermodynamics and kinetics of phase separation of polymer mixtures have benefited greatly from theories of spinodal decomposition and of classical nucleation. In fact, the best documented tests of the theory of spinodal decomposition have been performed on polymer mixtures. 

Cahn s linear theory for spinodal decomposition is difficult to test in mixtures of simple liquids, because phase separation occurs so rapidly that the range of validity of the linear theory is typically exceeded before data can be acquired. In polymeric mixtures, however, phase separation is much slower, and tests of the theory are easier. For polymers of not-too-... 

Two sets of experiments on phase separation kinetics have been performed. The first series of experiments was designed to demonstrate the feasibility of using excimer fluorescence to test Cahn s kinetic treatment of the early stages of spinodal decomposition. 

Research on the spinodal decomposition of polymer solutions and mixtures began in relatively recent years, but a considerable body of experimental data has already been accumulated by several groups of workers. Major findings have been reviewed by Hashimoto [ 19, 20] and Nose [21], along with a relevant summary of the related theories. In this section, we describe some typical studies on polymer spinodal decomposition performed mainly to test the theoretical predictions mentioned in the preceding sections. We do not intend an extensive or complete survey of related papers. 

Snyder et al. [23] were among the earlier workers who studied the early stage of spinodal decomposition of polymer blends, with the distinct aim of testing the Cahn-Hilliard theory. They measured /total as a function of time for three PS/PVME blends and found that ln(/total ) increased linearly with time t over a certain range of early time. If R k) defined by eq 2.8 has a sharp maximum at fc = Fni> eq 2.7 may be approximated by u x,t) e.xp (//(fcni)t), so that exp (2/ (fcm)t). Therefore, the initial slope of ln(/totai ) vs. t can be equated to R(km)- Snyder et al. used this idea to analyze their data (the same idea had already been used by Nishi et al. [11]). However, we have to note that the peak of R k) given by eq 2.8 is not so sharp as to justify the approximation used. 

Typical Data As cited by Hashimoto 119] and Nose [21], many experiments have ben done concerning the later stage (defined here as the intermediate plus the late) of spinodal decomposition of condensed binary polymer mixtures. Actually, much of them has focused on testing the dynamic scaling laws for S k,t), km, and discussed in Section 2.6. 

Flory P.J. Principles of Polymer Chemistry. Ithaca, NY Cornell University Press, 1971 de Gennes P.G. Scaling Concepts in Polymer Physics. Ithaca, NY Cornell University Press, 1979 Hashimoto T., Itakura M., Hasegawa H. Late stage spinodal decomposition of a binary polymer mixture. I. Critical test of dynamical scaling on scattering function. J. Chem. Phys. 1986 85 6118-6128... 

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