Influence of a density mismatch on TMPTMA shells non concentricity

Some laser target designs require low-density organic foam shells to study fusion on the French high-power laser laser mega joule. Low-density trimethylolpropane trimethacrylate foam shells composed of C, H, and O, 2 mm diameter, 100-μm wall thickness, and 250 mg cm-3 density are synthesized by a microencapsulation technique using a droplet generator. These shells have to reach a sphericity higher than 99.9% and a non-concentricity (NC) lower than 1%. The wall thickness variation is one of the most difficult specifications to meet. An important factor in reducing this defect is the density matching between the three phases of the emulsion at polymerization temperature. The influence of a density mismatch between the internal water phase and the organic phase on the NC of TMPTMA foam shells was studied. The best NC results and yields of shells are obtained with a density gap between the internal water phase and the organic phase of 0.078 g cm-3 at 60 degrees C, with an average NC around 2%. (authors)