Mesoporous Micro- and Nano- particles prepared by Evaporation-Induced Self Assembly within Aerosols

Evaporation induced self assembly (EISA) within microdroplets produced by a vibrating orifice aerosol generator (VOAG) has been used to produce monodisperse mesoporous silica particles. This process exploits the concentration of evaporating droplets to induce the organization of various amphiphilic molecules, effectively partitioning the silica precursor (TEOS) to the hydrophilic regions of the structure. Promotion of silica condensation, followed by removal of the surfactant, provides ordered spherical mesoporous particles. Using the VOAG, we have produced highly monodisperse particles in the 5 to 10 µm diameter range. The cationic surfactant CTAB typically leads to hexagonal mesostructure with mean pore size of about 2 nm and specific surface area around 900 m2/g. We have also shown that the pore size in CTAB-templated particles can be increased to 3.8 nm by incorporating trimethylbenzene as a swelling agent. The TMB preferentially locates inside and swells the hydrophobic regions of the surfactant mesostructure. Pore size can also be varied by the choice of amphiphile. Hexagonally ordered particles have been produced using the nonionic surfactant Brij-58 and block copolymer F127. These powders possessed mean pore size 2.8 nm and 6.9 nm, respectively. The uptake of alkyl pyridinium chloride molecules have recently been measured, revealing an uptake capacity that is explained by surface adsorption (as opposed to simple pore infiltration). Kinetics of the uptake process are still be analyzed.

References:

Monodisperse Mesoporous Microparticles Prepared by Evaporation-Induced Self-Assembly Within Aerosols. Rathod, SB; et. al., MAT. RES. SOC. SYMP. PROC.; 2003; v.775, p. P1.11.1-P.1.11.6