Structure of polymer solutions containing fumed silica.

Small angle neutron scattering is employed to estimate the interactions in complex multicomponent systems. The method is applied to describe a ternary system, poly(dimethyl siloxane) toluene with silica filler particles. Contrast variation by solvent deuteration is used to distinguish the three different partial structure factors of filled polymer samples, S(pp)(q), S(pf)(q), and S(ff)(q), where the subscripts p and f refer to polymer and filler. This procedure allows changes to be detected in the distribution of the polymer close to the solid surface. Independent dynamic light scattering measurements are used to validate the method. A comparison is made between the behavior of different filled poly(dimethyl siloxane) PDMS samples. It is found that the polymer distribution is perturbed in the vicinity of the solid surfaces. In the case of weak interactions, the solvent removes the polymer almost completely from the filler particles, while, when the interaction is strong, the surface remains covered.