Role of softness on transition temperatures for pNIPAM microgels

TL;DR

This paper explores how the softness of pNIPAM microgels, controlled by crosslinking density, affects their transition temperatures, using experimental measurements to deepen understanding of their thermoresponsive behavior.

Contribution

It provides new insights into the relationship between microgel structure and transition temperatures, aiding in the design of optimized thermoresponsive microgels.

Findings

Transition temperature differences depend on microgel softness.

Higher crosslinking density leads to distinct transition behaviors.

Results inform microgel design for targeted applications.

Abstract

Poly(N-isopropylacrylamide) (pNIPAM) microgels are renowned for their thermoresponsive behavior, exhibiting a distinct volume phase transition (VPT) upon temperature changes. This study investigates the influence of microgel softness, controlled by varying the crosslinking density during synthesis via free radical polymerization (FRP), on the difference between the volume phase transition temperature (VPTT) and the electrokinetic transition temperature (ETT). These transition temperatures mark the points at which the microgel size and surface charge, respectively, undergo significant alterations in response to temperature. Here, we investigate this phenomenon, employing dynamic light scattering (DLS) and electrophoretic light scattering (ELS) measurements to characterize the size and electrophoretic mobility response of pNIPAM microgels with different crosslinking densities as a function of temperature. By analyzing the observed trends in the difference between the transition temperatures, we aim to develop a hypothesis that provides a deeper physical understanding of the microgel structure and its relationship to transition temperatures. This investigation thus sheds light on the intricate interplay between microgel structure and its thermoresponsive behavior, offering insights for the design and optimization of pNIPAM microgels for future applications.