Chain dynamics in binary polymer mixtures

In disagreement with the previous theories, the new experimental data indicate that the terminal relaxation time associated with the long chains decreases systematically with the short chain length and with the weight fraction &phis; of the long chains. These experimental observations have inspired the proposal of a new reptation theory to account for (1) the tube dilation due to the constraint release by short chains, (2) impedance of the long chain's curvilinear diffusion and (3) enhanced contour length fluctuation, all resulting from the incorporation of the short chains of length N_S.; Furthermore, we have studied the diffusion and rheological behavior of binary mixtures over the full composition using pulse-gradient NMR and oscillatory shear measurements. These experimental observations along with additional theoretical analyses have allowed a clear identification of different regimes in a dynamic “phase” diagram where the two axes are the probe chain's molecular weight N_P and matrix molecular weight N _M respectively.; In the dilute limit of the long chains, we focuses on the comparison between the theoretical predictions and rheological measurements of mixtures made of the entangling long chains dissolved in matrices of short chains of length N_M with either N_M > N_e or N_M < N_e, where N_e is the critical chain length for entanglement. This investigation allows us to establish the trace chain dynamics in the various regimes.