A PARAMETRIC STUDY OF MICROENCAPSULATION APPROACH TO THE PREPARATION OF POLYSTYRENE SHELLS

Spherical polystyrene shells for laser fusion experiments were made in a density-matched microencapsulation approach. The yield, diameter, w all thickness, vacuole content, and surface finish were determined for different polystyrene concentrations varied from 5 to 13 wt% in an eq uivolume mixture of toluene and 1,2-dichloroethane, and an internal wa ter phase containing surfactants, Tween 40 and Brij 30, at concentrati ons of 0.05 and 0.1 wt%, respectively. The main observations are: (1) The yield of shells is improved with added surfactants, and the effect is more pronounced at a higher polymer concentration; (2) The outer s hell diameter increased with added surfactants at a constant polymer c oncentration. This is attributed to larger droplets being more stable in the first stage of the fabrication process; (3) Thicker shell walls are achieved with higher polymer concentrations; (4) The outer shell diameter increased with increasing polymer concentration regardless of added surfactants. This is attributed to a thicker wall providing gre ater mechanical stability; (5) The number of vacuoles over the cross-s ectional area of the wall increases with increasing polymer concentrat ion and with the addition of surfactants; and (6) The shells possess a smooth surface with a root-mean-square surface roughness less than 25 nm over a 30 mu m x 30 mu m area, and asphericity greater than 99.6%. (C) 1997 Elsevier Science Ltd.