The dynamics of polymer blends: interdiffusion and the glass transition

Abstract

In this paper it is shown, on the basis of a simple mean field approach to the dynamics of concentration and density fluctuations, that the interdiffusion coefficient D _int(ϕ) in a blend (A/B) of composition ϕ can be related to the self-diffusion coefficients D*_A/B of the pure melts. However, the relation is predicted to be a linear combination of the so-called fast and slow modes: D ⁻¹_int =(1−U){D ^*_slow }⁻¹+ U{D ^*_fast }⁻¹.

The parameter U=U(T) is given and is shown to be a measure of the nearness of the glass transition to the experimental temperature T. Far above the glass transition (U→0) the interdiffusion coefficient reduces to D*_slow and should show the simple linear dependence on concentration according to {D ^*_slow }⁻¹={ϕD ^*_A }⁻¹+{(1−ϕ) D ^*_B }⁻.