A parametric study of microencapsulation approach to the preparation of polystyrene shells

Abstract

Spherical polystyrene shells for laser fusion experiments were made in a density-matched microencapsulation approach. The yield, diameter, wall thickness, vacuole content, and surface finish were determined for different polystyrene concentrations varied from 5 to 13 wt% in an equivolume mixture of toluene and 1,2-dichloroethane, and an internal water phase containing surfactants, Tween 40 and Brij 30, at concentrations 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 shell diameter increased with added surfactants at a constant polymer concentration. 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 greater mechanical stability; (5) The number of vacuoles over the cross-sectional area of the wall increases with increasing polymer concentration 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 μm × 30 μm area, and a sphericity greater than 99.6%.