Microencapsulation Process Factors Which Influence the Sphericity of 1 mm o.d. Poly(α-Methylstyrene) Shells for ICF

We have identified three process variables which determine the sphericity of polymer shells made by dual orifice microencapsulation. 1) The density mismatch between the outer aqueous solution and the polymer oil phase must be minimized. We have minimized this density mismatch by adjusting the water bath temperature. 2) The stir rate has an effect, with a minimum non-sphericity located near 50–70 rpm stir rate. 3) The outer aqueous solution must have enough total oil solvent (fluorobenzene in the drops) to be beyond the aqueous saturation level (1.5 g/ℓ) at the beginning of the solvent extraction. Using the optimal conditions for a 1000 μm o.d. shell, we produce a minimum variation in the radius of a given shell, in the neighborhood of 0.4 μm.