Molecular dynamics simulations of relaxation in stretched PVDF nanofibers
JY Miao and RS Bhatta and DH Reneker and M Tsige and PL Taylor, POLYMER, 56, 482-489 (2015).
We analyze by means of atomistic molecular-dynamics simulations and analytical theory the relaxation processes that occur following the formation of thin electrospun nanofibers of poly(vinylidene fluoride). We find the relaxation processes that follow formation of a nanofiber to be of two types. One type is a rapid rotation of chain segments that gives rise to twist defects at various points along the chain. In the second type, twist defects translate until they are near to other, similar defects, at which point they stop and assemble into twist boundaries that include several chains. This sequence is reflected in the time variation of the distribution of dihedral angles of the chains, where an initial broadening of the distribution about the trans conformation is followed by a narrowing that restores the distribution almost to its original form. Reducing the radius of the nanofiber to below 2 nm lowers the stability of the ordered phase, so that even at zero temperature the ferroelectric order quickly diminishes, while at room temperature the relaxation times become very short. Regardless of how small the fiber diameter is, however, twist boundaries continue to form. (C) 2014 Elsevier Ltd. All rights reserved.
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