Strengthening of a polymer interface: Interdiffusion and cross-linking

In many industrial processes, pieces of the same polymer material are broug ht into contact at a temperature above the glass transition. Interdiffusion takes place across the interface and leads to a strengthening of the junct ion. Often, a cross-linker agent is also added in order to improve the glob al mechanical properties of the material, as in the formation of latex film s from dispersed solutions of polymer particles. We studied theoretically t he competition between the interdiffusion and the cross-linking reaction, a nd found that the control parameter tuning; the balance between these two p rocesses is alpha = Q tau (0)A(0)*N(3)b(3)/N-e, where Q tau (0) accounts fo r the reactivity of the cross-linker, A(0)* is the initial concentration of sites capable of cross-linking on the polymer chains, N is the polymerizat ion index, N, the number of segments between entanglements, and b a distanc e comparable to the segment length. The case of practical interest is alpha much less than 1: the reaction locks the interfacial chains once a signifi cant mixing has developed, resulting in films with goad mechanical properti es.