New technique allowing the quantification of diffusion at polymer polymer interfaces using rheological analysis: Theoretical and experimental results

A new technique allowing the quantification of diffusion at polymer/polymer interfaces and also measurement of the self-diffusion coefficient of polymer melts using rheological tools has been developed. The technique consists of measuring the dynamic moduli as a function of time for a multilayer sandwich-like assembly at temperature slightly above Tg. The technique was tested on a polystyrene/polystyrene (PS/PS) system sheared in oscillatory mode under small amplitudes of deformation for different times of welding. The experimental results showed that the dynamic complex shear modulus increased with the elapsed time of welding. The increase was attributed to the diffusion of polymer chains at the superimposed interface layers. Based on the reptation theory, an analytical expression for the self-diffusion coefficient as a function of polymer rheological material functions was derived. Graessley's expression [Graessley (1980)] for the bulk self-diffusion coefficient is recovered as a special case. The obtained self-diffusion coefficient for polystyrene was found to be in good agreement with the literature data reporting the self-diffusion coefficient of PS measured by classical techniques. (C) 1999 The Society of Rheology. [S0148-6055(99)01303-6].