Some Aspects of the Hydrodynamics of the Microencapsulation Route to NIF Mandrels

Abstract

Spherical plastic shells for use as mandrels for the fabrication of ICF (Inertial Confinement Fusion) target capsules can be produced by solution-based microencapsulation techniques. The specifications for these mandrels in terms of sphericity are extremely rigorous, and it is clear that various aspects of the solution hydrodynamics associated with their production are important in controlling the quality of the final product. This paper explores what we know (and need to know) about the hydrodynamics of the microencapsulation process in order to lay the foundation for process improvements as well as identify inherent limits.

Solvent removal during curing process of highly spheric and monodispersed-sized polystyrene capsules from density-matched emulsions composed of water and benzene/1,2-dichloroethane

“…The emulsion to prepare the polystyrene shell consists of water and oil as W 1 /O/W 2 , where W 1 , O, and W 2 are the inner water phase, the oil phase containing polystyrene as a capsule material, and the outer water phase, respectively. The densities of the three phases should be well matched, producing highly spherical (99.8%) and very precise capsules 6–16. Monodispersed 4‐mm‐in‐diameter capsules were prepared using an emulsion generator with a triple orifice 13.…”

“…Further investigation based on fundamental processes is required to simplify the complicated parameters and expand the application of the method for other polymer capsules. Recent theoretic and experimental studies have shown that nonuniformity is derived from a slight mismatch in the density between the W 1 and O phases and that de‐formation of the emulsion causes a centering force of the W 1 phase against the O phase 6–10. In order to prepare a uniform shell, the emulsion repeatedly must be de‐formed before the emulsion loses its fluidity.…”