The Use of CaCl₂ and other Salts to Improve Surface Finish and Eliminate Vacuoles in ICF Microencapsulated Shells

Polystyrene and poly(α–methylstyrene) (PAMS) shells made by microencapsulation are prone to having vacuoles in the walls and a concommitant surface roughness. These defects can be detrimental to the implosion required for ICF shots. We have found that adding sufficient salt (typically CaCl₂ or NH₄Cl) to the exterior polyvinylalcohol (PVA) solution during the drying phase inhibits the formation of vacuoles and decreases the surface roughness of the shells. The use of such salts does affect other shell specifications, for which other process variables must be adjusted.