SOL OR GEL-LIKE BEHAVIOR OF IDEAL SILICA SILOXANE MIXTURES - PERCOLATION APPROACH

Properties of idealized silica-siloxane mixtures are described within the framework of a percolation process. Polymer chains are considered as bifunctional units of percolation. Silica particles are considered as units of percolation with a high functionality, f(c) (f(c) congruent-to 10(2)); f(c) is determined by the process of chain adsorption which results from the formation of hydrogen bonds with the silica surface. The state of gelation of a given mixture is characterized by using three variables: the initial specific amount of polymer Q(i), the specific amount of adsorbed polymer Q(r), and the chain molecular weight M(n)BAR. A diagram is proposed to distinguish domains where an infinite cluster is formed from domains in which the clusters formed have a finite size. Expressions of the modulus of elasticity above the threshold of percolation are proposed.