Effect of Solvent Casting on Morphology

While the equilibrium thermodynamic approaches of Meier (1969,1970, 1971) and Inoue et al (1970a,h) predict that particular compositions will have particular fine structures, several investigators have shown that materials cast from different solvents and subsequently dried differ from each other and from materials prepared from the melt. As an example, let us examine the effects of the following solvents on a typical styrene-butadiene-styrene block copolymer benzene/heptane 90/10 tetrahydro-furan/methyl ethyl ketone 90/10, and carbon tetrachloride (Beecher et al, 1969). The particular compositions were chosen to give selective solvating behavior. While benzene dissolves both blocks, the heptane component, which evaporates last, swells only the butadiene block. Tetrahydrofuran is also a mutual solvent it evaporates first, leaving methyl ethyl ketone, which swells only the polystyrene block. Pure carbon tetrachloride is a mutual solvent. (Examples of swelling crystalline block copolymers are considered in Chapter 6.) 

A serious doubt arises about the phase domain stability of solvent-cast materials. Certainly not all of them (perhaps none ) are in true thermodynamic equilibrium. Yet the difficulty of migration of one block type by diffusion through the A phase of the other, especially at room temperature and below, probably results in a series of pseudoequilibrium states that can maintain their identity for long periods of time. 

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