  We study stress relaxation in bi-disperse entangled polymer solutions.
Shorter chains embedded in a majority of longer ones are known to be oriented
by coupling to them. We analyze the mechanism for this both by computer
simulation and theoretically. We show that the results can be understood in
terms of stress fluctuations in a polymer melt and chain screening. Stress
fluctuations are frozen on the relaxation time of the longer chains, and these
will induce strong orientational couplings in the shorter chains.
