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Atomistic Molecular Dynamics Simulations of the Lower Critical Solution Temperature Transition of Poly(N‑vinylcaprolactam) in Aqueous Solutions
journal contribution
posted on 2019-05-24, 00:00 authored by Xiaoquan Sun, Xianghong QianPoly(N-vinylcaprolactam) (PVCL) is a thermo-responsive
polymer, which exhibits a lower critical solution temperature (LCST)
in an aqueous solution. The LCST of this hydrophilic-to-hydrophobic
transition is found to be strongly dependent on the salt-type and
salt-concentration as well as on the molecular weight and concentration
of the polymer. Here, atomistic molecular dynamics simulations have
been successfully conducted for the first time to investigate the
LCST transition of a 100 degree of polymerization PVCL chain in water,
1 M NaCl, 3.5 M NaCl, and 0.5 M CaCl2 solutions. Our results
show that steric hindrance resulting from the bulky 7-member ring
on the PVCL chain plays a critical role in the conformational transition.
Moreover, the degrees of hydration and dehydration below or above
the transition temperature are highly dependent on the specific solution
condition and temperature. Water molecules are found to be trapped
inside the collapsed polymer chains leading to the varying degrees
of hydration and dehydration of the polymer chain in different solutions.
Calculated water diffusion coefficients for both trapped and free
water molecules agree very well with experimental measurements.