Insights into the tensile behavior of polymer nanofibers with hierarchically twisted chains

H Liu and CH Wang and J Tan and WM Yang and LS Cheng, COMPUTATIONAL MATERIALS SCIENCE, 194, 110463 (2021).

DOI: 10.1016/j.commatsci.2021.110463

Polymer fibers twisted in a nanoscale are of interest in energy-related materials and devices. Molecular dynamics simulations with a united-atom model were carried out to get insights into the tensile behavior of polymer nanofibers with hierarchically twisted polyethylene chains. The strain-stress curve and tensile strength were calculated for the nanofibers with various twisting angles. We also analyzed the microstructure and the effects of twisting on the contributions of bond stretching to the tensile strength of the nanofiber. The obtained results indicate that the tensile strength of the twisted nanofiber first decreases and then increases with increasing the twisting angle. The tensile strength of the considered nanofibers has the minimum when it is twisted for 107c and it is enhanced when it is twisted for 507c compared to that of the untwisted one. We found that the density of the nanofiber is more condensed in the radial direction when it is twisted than that of the normal fiber, and the condensed extent increases with the twisting angle. Twisting has two effects on the mechanical properties of the nanofiber. It reduces the contribution of bond stretching to the tensile stress and weakens the tensile strength of nanofiber. However, it can also increase the tensile strength of the nanofiber by enhancing the interchain friction and decrease the slipping between chains. This work provides a better understanding of the twisted polymer nanofiber, which may be helpful for the optimized design of functional materials and devices for energy applications, such as high actuation stress and strain artificial muscles and high-energy microengines.

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