Diffuse interface between polymers: Structure and kinetics

Abstract

AbstractThe interfacial structure and diffusion kinetics of two compatible polymers, poly(methyl methacrylate) and poly(vinylidene fluoride) are studied in the melt. The interdiffusion rates of the two components are found to be unequal, giving unequal diffusion coefficients, a net mass flow across the interface, and an asymmetric interfacial composition profile. The structure and kinetics confirm the predictions of the reptation theory. The interfacial thickness d grows with t1/2, and the interdiffusion coefficient is proportional to M−2, where t is the time and M is the molecular weight. The scaling law for the interfacial thickness is therefore d ∝ M−1t1/2. The number of chains per unit area crossing the original interface reaches a constant value independent of diffusion time after a short induction time on the order of the tube disengagement time (about 0.1–10 s in the present cases depending on the molecular weights). The adhesive bond strength σ is scaled by σ ∝ t1/4M−1/2 and σ/σ∞ ∝ t1/4M−1/2 [1‐ (Mc/M)]−1, where σ ∞is the σ at infinite molecular weight and Mc is the entanglement molecular weight.