Thermoresponsive Toughening in LCST-Type Hydrogels: Comparison between Semi-Interpenetrated and Grafted Networks

TL;DR

This study compares semi-interpenetrated and grafted LCST-type hydrogels, revealing how network topology influences thermoresponsive behavior and mechanical properties, with significant improvements observed in certain configurations.

Contribution

It provides a comparative analysis of semi-IPN and grafted hydrogels, highlighting how topology affects phase separation and mechanical performance in thermoresponsive hydrogels.

Findings

Semi-IPN with linear PNIPA forms microdomains upon phase transition.

PDMA network interpenetrated by linear PNIPA shows limited mechanical enhancement.

PDMA interpenetrating crosslinked PNIPA significantly improves mechanical properties at high temperature.

Abstract

Hydrophilic and LCST polymer chains, poly(N,N-dimethylacrylamide) (PDMA) and poly(Nisopropylacrylamide)(PNIPA), were combined in semi-interpenetrated architectures toinvestigate their responsive properties in swollen isochoric conditions comparatively tografted network structures. Using equal weight fractions of PDMA and PNIPA, semi-IPNdesigned with opposite topologies have demonstrated a thermoresponsive behavior with verydifferent structure/properties relationships as investigated by calorimetry, swellingexperiments, tensile tests and 2D neutron scattering at rest and under deformation. In the caseof the PDMA network interpenetrated by linear PNIPA chains, the phase transition of PNIPAgives rise to the formation of large microdomains, loosely percolating the PDMA network.Above the transition, the enhancement of the mechanical properties remains low in terms ofelastic modulus and fracture energy. Conversely, the opposite topology, with PDMA chainsinterpenetrating the crosslinked PNIPA network, brings a large improvement of themechanical properties at high temperature with a 10-fold increase of the modulus and veryhigh fracture energy. By comparison with grafted hydrogels of similar composition anddifferent topologies, the impact of the primary structure over the phase-separated morphologyand the resulting mechanical properties was clearly highlighted.