Solvent exchange kinetics in poly(N-isopropylacrylamide) microgel-based etalons

Poly (N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgel-based etalons are constructed by depositing thin Au layers (mirrors) on either side of a planar microgel layer. When immersed in water, the microgel layer swells and the etalon exhibits visual color. The thermoresponsivity of the pNIPAm-based microgels allows the Au mirror spacing, and hence the device color, to be dynamically modulated. Necessarily, when the mirror spacing is modulated solvent in the microgel layer must be expelled to the surroundings. Previously, we determined that the etalon deswelling kinetics depended critically on the thickness of the Au layer covering the microgels. Here, we report on solvent exchange kinetics. We found that the time required for solvent entry into the microgel layer is much longer than solvent exit. In addition, the rate was found to again depend critically on the thickness of the Au layer covering the microgel layer; thicker Au layers corresponded to slower solvent exchange kinetics.