Revisiting crosslinking density effects on pNIPAM microgel properties: Size, electrophoretic mobility, and transition temperatures.

This article focuses on investigating how the crosslinking density affects the thermoresponsive properties of poly(N-isopropylacrylamide) (pNIPAM) microgels, specifically their size, electrophoretic mobility, stiffness, and transition temperatures. Using 20 batches of pNIPAM microgels synthesized via conventional one-pot and semi-batch methods, the study employs dynamic light scattering, electrophoretic light scattering, and atomic force microscopy to characterize these properties. Results show that increasing crosslinking density decreases the swelling ratio and hydrodynamic diameter in the swollen state but increases the diameter in the collapsed state, while electrophoretic mobility remains relatively constant due to fixed initiator amounts. Importantly, both the volume phase transition temperature (VPTT) and electrokinetic transition temperature (ETT) increase with crosslinking density, with ETT rising more significantly, and microgels with homogeneous crosslinking exhibit a smaller difference between these transition temperatures compared to core–corona structured microgels. These findings provide insights for tailoring pNIPAM microgels' structural and thermal properties for applications such as drug delivery and sensing.