Relaxation of concentration fluctuations in entangled polymer mixtures .1.

The dynamics of composition fluctuations in entangled compatible polymer blends are considered theoretically using the reptation model. Both symmetric and asymmetric (long + short chains) mixtures are considered. It is shown that the relaxation dynamics is generally non-exponential and is characterized by 4 sets of modes: two reptation modes (fast and slow) corresponding to diffusion of mainly short chains and mainly long chains respectively, and two Rouse modes. It is also shown that two theoretical concepts of fast and slow diffusion are both valid in a Limited region of wave-lengths, where the theories adequately describe the corresponding relaxation processes.