A RHEOLOGICAL STUDY ON THE CHAIN INTERDIFFUSION OF MISCIBLE POLYMER MELTS

A sandwich-like sample configuration of three polymer layers was designed and used for rheological probing of the chain interdiffusion of two miscible polydisperse polymers in the melt state. It was found that the interdiffusion process can be probed by the growth of the rheological responses with time as long as the polymer pair constituting the interface has an adequate difference in rheological properties and is miscible. To understand the theological signal of the interdiffusion process, a phenomenal rheological model combined with a fitted model for the experimental data was proposed. With the two models, two important model parameters concerning the interdiffusion dynamics were discussed. The results show that the interdiffusion process can be probed by rheological properties and the dynamics of inter diffusion is greatly affected by the difference in the molecular weight between the polymer pair. The first parameter, the exponent alpha for the time dependent behavior of the interpenetration distance,was found to be larger than the typical value of 1/2, which is ascribed to the dynamic dilution process as proposed in tube theories. While,by the other parameter, the characteristic time t(e), the interdiffusion coefficient can be estimated. It is noted that these two parameters were found to be frequency-dependent, which can be mainly ascribed to the polydispersity of the molecular weight. Finally, the results indicate that the fast-mode model is reasonable for the understanding of the interdiffusion process.