SANS study of the thermodynamics and demixing of highly interacting PaMSAN/dPMMA blends

Spinodal decomposition of partially miscible polymer blends has the potential to generate well-defined polymeric nanostructured materials. While the Cahn-Hilliard (CH) theory prediction for the initial spinodal lengthscale generally holds, phase sizes attained by thermally-induced demixing are, however, stubbornly much greater that Rg. Using Small Angle Neutron Scattering (SANS), we investigate a series of LCST poly(a-methyl styrene-co-acrylonitrile) and deuterated poly(methyl methacrylate) (PaMSAN/dPMMA) blends which exhibit a remarkably steep temperature dependence of G’’ (and thus c), the driving force for demixing [1,2]. We explore the role of PMMA molecular mass (MW= 40-130 kg/mol), tacticity, composition, and temperature and to map G’’ and c as a function of these parameters in the one-phase region, employing Random Phase Approximation theory. We then carry out a series of rapid jumps into the unstable and metastable regions, establishing a comprehensive map of lengthscales achieved and theoretically expected, and limits and opportunities for bicontinuous nanostructure design by this approach.
[1] J. T. Cabral and J.S. Higgins, Prog. Polym. Sci. 81, 1-21 (2018).
[2] J.S. Higgins et al., Macromolecules 22, 3674-3681 (1989).