Recent investigations of the structure–property relationships in polymer nanocomposites have elucidated the role of nanoparticles in improving mechanical, optical and electrical properties in materials that then find their way into a wide array of applications. A critical challenge in obtaining such properties, however, is the fabrication of functionalized nanoparticles that are able to disperse well and favorably interact with the polymer matrix. In this work, we examine the thermodynamical interactions of polystyrene (PS) grafted onto spherical silica nanoparticles blended with a chemically-distinct poly(vinyl methyl ether) (PVME) matrix using light, x-ray and neutron scattering techniques. PS/PVME systems are of particular interest as they are known to exhibit a lower critical solution temperature, with blending behaviors greatly affected by the chain length of the components. Using scattering techniques, we study the enthalpic and entropic contribution to the dispersion of PS-grafted nanoparticles in a chemically-distinct matrix, especially as the system approaches a phase boundary. We also examine the effect of molecular weight on the blend thermodynamics, as well as the interplay among the tunable characteristics of the nanoparticles, on the phase behavior and concentration fluctuations for strongly interacting polymer blends of PS-silica hybrids and PVME. X-ray scattering data of the structure factor reveal that for a grafted deuterated polystyrene brush in a PVME matrix of 33,000 g/mol and 226,000 g/mol molecular weight, respectively, an initial dispersion of nanoparticles occurs at low temperatures. The system then gradually transitions to an aggregated state as temperature is increased, suggesting the presence of strong inter-particle interactions that lead to fractal formation as the system approaches a phase boundary. Complementary neutron scattering experiments confirm this phenomenon.

Phase behavior of polymer-grafted nanoparticles in a polymer matrix

249th National Meeting (2015)

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