Constraint Release in Entangled Binary Blends of Linear Polymers: A Molecular Dynamics Study Export

@article{wang08, abstract = {We present extensive molecular dynamics simulations of the dynamics of diluted long probe chains entangled with a matrix of shorter chains. The chain lengths of both components are above the entanglement strand length, and the ratio of their lengths is varied over a wide range to cover the crossover from the chain reptation regime to tube Rouse motion regime of the long probe chains. Reducing the matrix chain length results in a faster decay of the dynamic structure factor of the probe chains, in good agreement with recent neutron spin echo experiments. The diffusion of the long chains, measured by the mean square displacements of the monomers and the centers of mass of the chains, demonstrates a systematic speed-up relative to the pure reptation behavior expected for monodisperse melts of sufficiently long polymers. On the other hand, the diffusion of the matrix chains is only weakly perturbed by the diluted long probe chains. The simulation results are qualitatively consistent with the theoretical predictions based on constraint release Rouse model, but a detailed comparison reveals the existence of a broad distribution of the disentanglement rates, which is partly confirmed by an analysis of the packing and diffusion of the matrix chains in the tube region of the probe chains. A coarse-grained simulation model based on the tube Rouse motion model with incorporation of the probability distribution of the tube segment jump rates is developed and shows results qualitatively consistent with the fine scale molecular dynamics simulations. However, we observe a breakdown in the tube Rouse model when the short chain length is decreased to around NS = 80, which is roughly 3.5 times the entanglement spacing NeP = 23. The location of this transition may be sensitive to the chain bending potential used in our simulations.}, address = {Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136}, author = {Wang, Zuowei and Larson, Ronald G.}, citeulike-article-id = {2897622}, citeulike-linkout-0 = {http://dx.doi.org/10.1021/ma800680b}, citeulike-linkout-1 = {http://pubs.acs.org/doi/abs/10.1021/ma800680b}, day = {1}, doi = {10.1021/ma800680b}, journal = {Macromolecules}, keywords = {binary, blend, constraint-release, linear, md}, month = {July}, number = {13}, pages = {4945--4960}, posted-at = {2009-04-30 22:02:05}, priority = {2}, title = {Constraint Release in Entangled Binary Blends of Linear Polymers: A Molecular Dynamics Study}, url = {http://dx.doi.org/10.1021/ma800680b}, volume = {41}, year = {2008} }

TY - JOUR ID - wang08 L3 - citeulike-article-id:2897622 N2 - We present extensive molecular dynamics simulations of the dynamics of diluted long probe chains entangled with a matrix of shorter chains. The chain lengths of both components are above the entanglement strand length, and the ratio of their lengths is varied over a wide range to cover the crossover from the chain reptation regime to tube Rouse motion regime of the long probe chains. Reducing the matrix chain length results in a faster decay of the dynamic structure factor of the probe chains, in good agreement with recent neutron spin echo experiments. The diffusion of the long chains, measured by the mean square displacements of the monomers and the centers of mass of the chains, demonstrates a systematic speed-up relative to the pure reptation behavior expected for monodisperse melts of sufficiently long polymers. On the other hand, the diffusion of the matrix chains is only weakly perturbed by the diluted long probe chains. The simulation results are qualitatively consistent with the theoretical predictions based on constraint release Rouse model, but a detailed comparison reveals the existence of a broad distribution of the disentanglement rates, which is partly confirmed by an analysis of the packing and diffusion of the matrix chains in the tube region of the probe chains. A coarse-grained simulation model based on the tube Rouse motion model with incorporation of the probability distribution of the tube segment jump rates is developed and shows results qualitatively consistent with the fine scale molecular dynamics simulations. However, we observe a breakdown in the tube Rouse model when the short chain length is decreased to around NS = 80, which is roughly 3.5 times the entanglement spacing NeP = 23. The location of this transition may be sensitive to the chain bending potential used in our simulations. IS - 13 JF - Macromolecules AD - Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 EP - 4960 TI - Constraint Release in Entangled Binary Blends of Linear Polymers: A Molecular Dynamics Study VL - 41 SP - 4945 KW - binary KW - blend KW - constraint-release KW - linear KW - md AU - Wang, Zuowei AU - Larson, Ronald PY - 2008/07/01/ UR - http://dx.doi.org/10.1021/ma800680b ER -