Enhanced Swelling Using Photothermal Responsive Surface-Immobilized Microgels

Unprecedented quantitative assessment of the swelling behavior of surface-immobilized photothermal responsive microgels (PTRM) is reported. The PTRM were prepared by incorporating plasmonic gold nanoparticles (AuNPs) in thermo-responsive cationic microgels based on poly(N-isopropylacrylamide) (BM). The stimuli-responsive behavior of the microgels was investigated in aqueous suspensions using Dynamic Light Scattering (DLS) and on surfaces using a Quartz Crystal Microbalance with Dissipation (QCM-D) as well as with the Surface Forces Apparatus (SFA). Both the BM and PTRM in aqueous suspensions underwent a similar temperature-induced volume phase transition at around 35 degrees C. The complexation of AuNPs with the BM led to a decrease in the surface charge allowing to increase the surface grafting density. This favored a unidirectional upward swelling of the surface immobilized PTRM. The study reports significant photo-triggered swelling responses on surface with decreases in film thickness up to 82%.