Polymer-Polymer Interdiffusion

We correct an earlier theory of polymer diffusion for a mixture of long (L) and short (S) chains in a melt, all chains being chemically identical. The mixing can be understood by analogy with the kinetics of polymer dissolution: up to a time τ L (the reptation time of the L component) the L chains behave like a gel, progressively swollen by the S chains. Marker particles cannot move with respect to the gel, and follow its boundary displacement x ( t ). We find x ( t ) ∼ ( D S t ) 1/2 in agreement with a number of recent data. But the overall density of the mixture remains constant everywhere, and the process has nothing to do with an uneven distribution of vacancies.