(570f) The Effects of Volatile Organic Additives in Mesostructured Silica Particles Produced by Evaporation-Induced Self Assembly

It is now well-established that ordered mesoporous or mesostructured silica particles can be produced by exploiting the self assembly and subsequent liquid crystalline (LC) structures of surfactant molecules that develop as droplets undergo evaporation (evaporation-induced self assembly, EISA). Organic additives that swell the hydrophobic regions of the surfactant structures have been shown to be a convenient way to increase pore size in studies utilizing the traditional bulk hydrothermal synthesis method. However, the fate and effect of organic additives are more complex in particle synthesis using EISA due to the competition between evaporation and partitioning to the hydrophobic LC domains. We have conducted EISA synthesis of mesostructured silica particles using the surfactant cetyltrimethylammoniumn bromide (CTAB), tetraethylorthosilicate, and organic additive trimethyl benzene with a range of initial droplet sizes and varied process conditions. These experiments reveal that this organic additive may have virtually no effect on the mesostructure or pore size under some conditions, may act as a typical swelling agent under other conditions, or may lead to unexpected mesostructural changes in the particles under appropriate conditions. These results combined with modeling of multicomponent droplet evaporation have allowed us to better understand EISA of droplets and the behavior of organic additives during EISA. Based on this, we are also able to develop empirical guidelines for the design of experimental systems to produce particles by aerosol EISA.