CONSTRAINT RELEASE IN POLYMER MELTS - TUBE REORGANIZATION VERSUS TUBE DILATION

We consider the concepts of reptation and constraint release to model the dynamics of polydisperse linear polymers. The mechanisms of constraint release at work in concentrated polymer solutions can be divided into two categories. Tube dilation occurs when constraint release causes a widening of the effective tube confining the chain. Tube reorganization refers to relaxation of the tube due to motion of the surrounding chains without changing the effective tube diameter. By comparing the motion of the chain with the motion of the tube, we determine the effective tube diameter and conclude that the tube only dilates when some of the constraints are below the entanglement molecular weight. In binary mixtures of long and short chains that have entanglements between the long chains, Rouse motions of the tube are only allowed up to the length scale of entanglements between the long chains, a(L). We suggest that tube reorganization beyond those length scales occurs by reptation of the tube in the supertube of diameter a(L). Experimental tests are suggested to distinguish between the predictions of the newly proposed process of tube reptation and the older idea of tube dilation.