The use of CaCl2 and other salts to improve surface finish and eliminate vacuoles in ICF microencapsulated shells

Polystyrene and poly(alpha-methylstyrene) (PAMS) shells made by microencaps ulation are prone to having vacuoles in the walls and a concommitant surfac e roughness. These defects can be detrimental to the implosion required for ICF shots. We have found that adding sufficient salt (typically CaCl2 or N H4Cl) to the exterior polyvinylalcohol (PVA) solution during the drying pha se inhibits the formation of vacuoles and decreases the surface roughness o f the shells. The use of such salts does affect other shell specifications, for which other process variables must be adjusted.