The Revealing of Heterogeneities by Free Linear Chains in a Network

Abstract

Using Small-Angle Neutron Scattering (SANS) we first, studied Methylmethacrylate (MMA) gels with no free chains of polystyrene (PSD) inside them. Gels show increased scattering compared to the solutions, contrary to the predictions of the classical theories. Second, linear PSD chains (their c<c*) were introduced in the system: again increased scattering is observed from chains in the gel compared to the chains in an equivalent semi-dilute solution. These results imply that when the translational entropy of free PSD chains is weak (especially for the larger ones) they would tend to mix less efficiently with the gel than with the solution. At low q, the scattering from the PSD chains increases with molecular weight and progressively tends to a master curve varying as q^-2.5. We discuss an explanation of this effect in terms of the percolation model of heterogeneities. The larger molecular weight PSD chains define the contour of the large percolation clusters in the gel.