Issue 3, 2020

Reduction of water-mediated repulsion drives poly(N-vinylcaprolactam) collapse upon heating

Abstract

Upon heating, thermo-sensitive aqueous polymers undergo the coil-to-globule transition, where drastic chemical and structural transformations occur that are of great interest for academia and applications. Although it is widely believed that the disruption of the clathrate-like hydration shell drives this polymer collapse, no decisive evidence has yet been provided. Here, we demonstrate, using all-atom molecular dynamics simulations, that poly(N-vinylcaprolactam) in water has a less ordered hydration structure than the bulk liquid and undergoes the coil-to-globule transition without remarkable hydration shell depletion or qualitative transformation. Furthermore, our free energy analyses show that water strongly pushes the “hydrophobic” caprolactam groups apart rather than bringing them together. We find that the reduction of this water-mediated repulsion, arising from the change in free energies for cavity formation, drives the polymer collapse upon heating.

Graphical abstract: Reduction of water-mediated repulsion drives poly(N-vinylcaprolactam) collapse upon heating

Supplementary files

Article information

Article type
Paper
Submitted
08 Here 2019
Accepted
11 Ker. 2019
First published
13 Ker. 2019

Phys. Chem. Chem. Phys., 2020,22, 1053-1060

Reduction of water-mediated repulsion drives poly(N-vinylcaprolactam) collapse upon heating

K. Mochizuki, Phys. Chem. Chem. Phys., 2020, 22, 1053 DOI: 10.1039/C9CP05491J

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