  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.
