Modeling of the processing dynamics of aerogel/gold nanoparticle composites

Colloidal gold nanoparticles were encapsulated in silica aerogels, and the dynamics of the gelling process in different solvents was investigated using visible spectroscopy. Modified Maxwell Garnett (MG) theory was used to model the behavior of aggregating gold nanoparticles in the silica network; our modifications incorporate additional filling factors with weighting components into the traditional MG equations to better fit experimental data. The introduction of 1-octanethiol protected Au nanoparticles to the aerogel matrix resulted in decreased aggregation of the particles and an unexpected blue shift in the surface plasmon resonance spectrum after solvent exchange from acetone to cyclohexane, with the plasmon peak moving from 558 nm to 529 nm. Such a shift did not occur in the non-thiol protected aerogel/nanoparticle composites. Our modeling indicates that modified MG theory is an effective means of tracking the physical/structural changes taking place during the solvent processing of porous silica gel/Au nanoparticle composites.