Hierarchical porous and composite particle architectures based on self assembly and phase separation in droplets

Abstract

Phase segregation between polymer and gelling silica has been utilized to introduce a controlled second level of porosity into mesoporous silica particles produced by evaporation-induced self-assembly (EISA) in aerosol droplets. During EISA within droplets, solvent evaporation leads to surfactant self-assembly, which introduces ordered mesoscale porosity into a silica matrix (after surfactant removal). In this work, it is shown that evaporation of aqueous droplets containing tetraethylorthosilicate (TEOS), surfactant cetyltrimethylammonium bromide (CTAB), and the hydrophilic polymer poly(acrylic acid) leads to hierarchically structured particles that display the mesoscale structure of the self-assembled surfactant and larger-scale domains introduced by phase separation of the polymer. Calcination of these particles produces hierarchically structured porous particles. The incorporation of the polymer does not interfere with the surfactant self-assembly or the resulting mesoscale porosity up to rather high levels of polymer loading. Variation of experimental parameters and conditions, such as the concentration of the polymer, solvent composition, and molecular weight of the polymer, has been shown to influence the structure and scale of polymer-derived voids within the particles, allowing the synthesis of single central voids (hollow particles), uniformly dispersed smaller voids, or a combination of these.