In situ photogelation kinetics of Laponite nanoparticle-based photorheological dispersions

In situ photorheology experiments were conducted to investigate the kinetics of UV-triggered photogelation of aqueous Laponite nanoparticle dispersions formulated with less than 10 wt% of a triblock copolymer (Pluronic F127) and diphenyliodonium-2-carboxylate monohydrate, a photoacid generator (PAG). We show that gelation kinetics depend strongly on solution composition and intensity of UV light used during in situ photorheology experiments. A decrease in gelation rate was observed with increasing Pluronic F127 concentrations while higher PAG and Laponite concentrations result in higher gelation rates. Changing the intensity of UV light from 100 mW cm(-2) to 150 mW cm(-2) at a constant composition reduced the exposure time required prior to onset of gelation by half. Finally, the effect of Laponite and PAG on the micellization of F127 was probed using differential scanning calorimetry (DSC). The results show that the presence of Laponite particles and PAG suppresses the enthalpic endotherm associated with micelle formation in solutions containing up to 7.2 wt% Pluronic F127. Using these results, we present a detailed mechanism for the photogelation phenomenon as well as the parameters surrounding intelligent design and formulation of these systems.