The role of polymer structure on water confinement in poly(N-isopropylacrylamide) dispersions

TL;DR

This study explores how the structure of PNIPAM polymers influences water confinement and crystallization behavior, revealing that microgels better prevent water crystallization compared to linear chains, with implications for low-temperature studies.

Contribution

It provides new insights into the impact of polymer topology on water-polymer interactions and crystallization, using DSC and light scattering techniques on different PNIPAM architectures.

Findings

Microgels more effectively prevent water crystallization than linear chains.

Polymer architecture significantly influences solution behavior and water confinement.

Isotopic substitution affects the solution dynamics and crystallization processes.

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) is a synthetic polymer that is widely studied for its thermoresponsive character. However, recent works also reported evidence of a low temperature (protein-like) dynamical transition around 225 K in concentrated PNIPAM suspensions, independently of the polymer architecture, i.e., both for linear chains and for microgels. In this work, we investigate water-polymer interactions by extensive differential scanning calorimetry (DSC) measurements of both systems, in order to understand the effect of the different topological structures on the solution behaviour, in particular regarding crystallization and melting processes. In addition, we compare protiated and deuterated microgels, in both water and deuterated water. The DSC results are complemented by dynamic light scattering experiments, which confirm that the selective isotopic substitution differently affects the solution behaviour. Our findings highlight the important role played by the polymer architecture on the solution behaviour: indeed, microgels turn out to be more efficient confining agents, able to avoid water crystallization in a wider concentration range with respect to linear chains. Altogether, the present data will be valuable to interpret future low-temperature investigations of PNIPAM dispersions, particularly by neutron scattering experiments.