Interplay of crosslinking architecture and interparticle interactions in microgel suspension rheology.

Abstract

HYPOTHESIS Poly(N-isopropylacrylamide) (PNIPAM) microgels are highly porous polymer networks whose mechanical properties are governed not only by environmental factors but also by their internal architecture. We hypothesize that the internal structure of microgels, together with interparticle interactions, synergistically regulates the macroscopic rheological behavior of microgel suspensions. EXPERIMENTS Frequency-sweep measurements were performed to identify the suspension states, evaluate shear-induced structural breakdown and recovery, and monitor continuous volume phase transitions under different conditions. The correlation between the loss tangent (tan(δ)) and the low-frequency power-law viscoelastic exponents were further analyzed. Critical transition points extracted from temperature sweeps were used to construct phase diagrams, describing phase distributions and transition pathways governed by temperature, concentration, and salt. FINDINGS Crosslinking architecture markedly altered the thermal response pathway of PNIPAM microgel suspensions and determined their ability to recover after shear-induced structural breakdown. Salt addition reshaped phase-transition pathways by screening electrostatic repulsion, while simultaneously amplifying architecture-dependent rheological differences among suspensions. These findings confirm that microgel suspension rheology is governed by the coupling between internal crosslinking architecture and interparticle interactions.