Role of a surface active agent in the sol-emulsion-gel synthesis of spherical alumina powders

Spheroidal alumina particles of tailor-made size were prepared by the sol-e mulsion-gel method under simultaneous mechanical agitation and sonication a nd by systematic variation of the concentration of a non-ionic surfactant i n the organic solvent ("oil phase") above or below the critical micelle con centration (CMC). The CMC of the surfactant in the organic solvent of low d ielectric constant was determined from discernible breaks in surface tensio n, viscosity, optical absorption and dye fluorescence vs. concentration cur ves. The CMC of the surfactant played an important role in controlling the sol droplet size and accordingly, the size of the alumina particles obtaine d therefrom. Transmission electron microscopy (TEM) revealed that near (but below) CMC the nanospheroids (10-50 m) were in the state of chain-like agg lomerates. Beyond CMC, spheroidal particles of larger dimensions were obtai ned. Particle size analysis showed a sharp decrease in mean size with incre asing concentration of the surfactant up to CMC, above which a gentle upwar d trend was noticed.