TRACER DIFFUSION IN FLUCTUATING BLOCK-COPOLYMER MELTS

We present a theoretical investigation of the tracer diffusion of dibl ock copolymers and homopolymers in a thermally fluctuating block copol ymer melt above the order-disorder transition (ODT) temperature. Entan glement effects and differences in monomeric friction coefficients are ignored; hence, the theory should be most applicable to short copolym ers with theologically similar blocks. Overall, we find that the diffu sion rates of both tracer block copolymers and homopolymers in a block copolymer melt are suppressed when compared with diffusivities in a s trictly homogeneous medium with the same average composition. This mob ility suppression is due to thermally excited composition fluctuations in block copolymer melts near the ODT; the latter result in transient potential barriers to diffusion. We explore the dependence of the tra cer diffusion coefficient on molecular weights and compositions of bot h matrix and tracer, as well as temperature. A comparison of our theor etical predictions to recent experiments by T. Lodge and coworkers sho ws qualitative agreement. (C) 1996 John Wiley & Sons, Inc.