Multiscale rheology model for entangled Nylon 6 melts
HY Liang and K Yoshimoto and M Kitabata and U Yamamoto and JJ de Pablo, JOURNAL OF POLYMER SCIENCE, 60, 3071-3084 (2022).
A multiscale simulation method is used to calculate the rheological properties of entangled Nylon 6 melts, including the stress relaxation modulus, storage and loss moduli, and the melt viscosity. The three- level multiscale approach includes all-atom, coarse-grained and slip- spring models, each operating at different levels of resolution and encompassing a wide range of length scales and over nine orders of magnitude in time. These models are unified by matching the polymer chain structure and dynamics as well as the stress relaxation, and together predict the rheological master curves at various temperatures using time-temperature superposition. The calculated viscosity agrees reasonably with experiment. The effect of polydispersity on rheology is also studied by simulating a polydisperse melt with chain lengths follow the Schulz-Zimm distribution. Under the same weight-average molecular weight, the polydisperse melt shows faster stress relaxation and lower viscosity compared to the monodisperse melt. For polymers that undergo rapid degradation at elevated temperatures, such as Nylon, the proposed approach offers a useful means to investigate rheology over a wide range of conditions. Importantly, the approach is fully predictive in that calculations of rheology are generated without relying on experimental information, and it therefore offers potential for design of polymeric materials on the basis of purely molecular models.
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