Mechanically induced sorption of siloxane on silica: Experimental and theoretical investigations of chain binding, collective behaviour and multiple-aggregate processes

The purpose of the present paper is to propose a two-parameter model to describe the sorption of siloxane chains onto silica particles immersed in the polymeric liquid at room temperature. Random adsorbed systems were obtained from mechanical mixing. One parameter of the model is the probability θ B that a polymer chain is simultaneously bound to two silica particles; the other one, π, attempts to describe the possible collective character of the binding of a single chain. The model was compared with values of the residual amount of polymer Q r measured siloxane-silica mixtures after removal of all free polymer chains. The number of available chain binding sites per unit mass of silica was varied by using a silica surface treated to a variable extent. Typical relative numbers of silicon chains ( M n ⋍ 3.6 × 10 5 ) simultaneously bound to two or three particles were found to be 0.21 and 0.49, respectively, in a mixture determined from an initial siloxane-silica weight-to-weight ratio equal to 2.5. Also, it was shown that a chain binding site can be divided into four subsites; on average, any chain is torn off from the surface whenever it occupies less than two subsites.