(15f) The Evolution of Internal Architecture in Particles Produced by Evaporation-Induced Self Assembly within Aerosols

Evaporation-induced self assembly of amphiphilic molecules in evaporating droplets has been demonstrated to be a versatile approach to producing silica particles with ordered mesoporosity. In this process, droplets of an aqueous or alcohol-based solution containing a silicate precursor and amphiphile evaporate, leading to amphiphile self assembly and eventual solidification due to silica condensation. Removal of the organics leaves the mesoporous particles. Pore size and mesostructure are influenced by the type of amphiphile or surfactant, additives, and also by the competing dynamic processes of evaporation, self assembly, and silica condensation. We have been investigating this rich parameter space to develop understanding and demonstrate synthetic strategies to produce porous particles with controlled multiscale porosity. Ordered pores in the 2-10 nm range are introduced by the choice of amphiphile or surfactant, sometimes with the help of an organic swelling agent. We see evidence that organic additives can also influence the mesostructural order of self-assembled surfactant structures in a complex manner that is related to the competing dynamic processes within droplets. We explore these dynamic effects by varying initial droplet size, droplet composition, silica condensation rate, and process residence times. The particles produced by these methods can be engineered to suit a variety of applications, including catalysis, controlled release and biomolecule sensing. The presentation will provide an overview of the synthetic method, with an emphasis on the role of competing dynamics in the determination of multiscale internal structure of particles. Examples of selected applications of particles will also be shown.