Improving the Wall Uniformity of Resorcinol Formaldehyde Foam Shells by Modifying Emulsion Components

Previously we have developed a production process for both standard density (100 mg/cc) and high-density (180-200 mg/cc) resorcinol formaldehyde (RF) foam shells with a triple orifice droplet generator. These foam shells are needed for direct drive inertial confinement laser fusion experiments on the OMEGA laser facility at the University of Rochester. Although this process has been developed into production mode, the yield of high density RF (HDRF) and standard density (SDRF) shells with acceptable wall uniformity has been poor. This yield depends on the type of RF shell that is being fabricated. For HDRF this yield is ~5% while for the SDRF shells the yield is ~30%. We have made improvements in the yield of these shells that meet the wall uniformity specification by modifying the composition of the outer oil solution (O2) in the microencapsulation emulsion. This improvement was achieved by a small addition (0.60 wt.%) of a styrene-butadiene-styrene (SBS) block copolymer into the outer oil (O2) solution that increased the interfacial tension of the emulsion system as well as the viscosity of the O2 solution. This modification improved the out of round and concentricity of the RF foam shells resulting in an increase in the yield of shells that meet the target wall uniformity specifications.