Chain and Ion Dynamics in Precise Polyethylene Ionomers
Christopher L. Soles, Amalie Frischknecht, Benjamin Paren, Robert Middleton, Karen Winey, Jason Koski, Madhu Sudan Tyagi, Jacob Daniel Tarver
We analyze the dynamics from microsecond-long, atomistic molecular dynamics (MD) simulations of a series of precise poly(ethylene-co-acrylic acid) ionomers neutralized with lithium, with three different spacer lengths between acid groups on the ionomers and at two temperatures. At short times, the intermediate structure factor calculated from the MD simulations is in reasonable agreement with quasi-elastic neutron scattering data for partially neutralized ionomers. For ionomers that are 100% neutralized with lithium, the simulations reveal three dynamic processes in the chain dynamics. The fast process corresponds to hydration librations, the medium-time process corresponds to local conformational motions of the portions of the chains between ionic aggregates, and the long-time process corresponds to relaxation of the ionic aggregates. At 600 K the dynamics are sufficiently fast to observe the early stages of lithium ion motion and ionic aggregate rearrangements. In the partially neutralized ionomers with isolated ionic aggregates, the Li-ion containing aggregates rearrange by a process of merging and breaking up, similar to what has been observed in coarse- grained simulations. In the 100% neutralized ionomers that contain percolated ionic aggregates, the chains remain pinned by the percolated aggregate at long times, but the lithium ions are able to move along the percolated aggregate.
, Frischknecht, A.
, Paren, B.
, Middleton, R.
, Winey, K.
, Koski, J.
, , M.
and , J.
Chain and Ion Dynamics in Precise Polyethylene Ionomers, Macromolecules, [online], https://doi.org/10.1021/acs.macromol.9b01712
(Accessed December 2, 2023)