An ultrasonic method to study the interdiffusion phenomenon between two polydimethylsiloxanes

We present an original method that allows the monitoring of the interdiffusion process between two miscible polymers. This acoustical method is nondestructive, and does not need any chain marking. It is based on the variations of the angular reflection coefficient R(θ) measured at fixed frequency, caused by the ultrasonic parameters modifications in the interphase during the diffusion process. We applied it to the interdiffusion between two polydimethylsiloxanes A and B of very different molecular weights. The evolution of R(θ) was also computed using successively the slow and the fast theories of diffusion, after calculation of the concentration profiles. The adjustment of the theoretical reflection spectra given by the slow theory on the experimental spectra allowed us to find the value the interdiffusion coefficient D0, which is characteristic of the system. This value is very near the value determined from the molecular dynamics laws (Rouse, reptation, Stokes–Einstein). But in the studied time domain, the fast theory accounts for the experimental results as well as the slow theory. Finally, we discuss the precision of the method and the means to improve it.