THE ROLE OF REACTANT TRANSPORT IN DETERMINING THE PROPERTIES OF NIF SHELLS MADE BY INTERFACIAL POLYCONDENSATION

Polymer shells up to 2 mm in diameter were prepared using an interfaci al polycondensation/cross-linking reaction occurring at the surface of an oil drop. The oil phase is comprised of a solution (20 wt% or less ) of isophthaloyl dichloride (IPC) dissolved in an organic solvent. An interfacial reaction is initiated when the IPC-loaded oil drop is sub merged in an aqueous solution of poly(p-vinylphenol) (PVP), a poly(ele ctrolyte) at elevated pH. Composition, structure, and surface finish f or fully-formed dry shells were assessed using a number of techniques including scanning electron microscopy (SEM), atomic force microscopy (AFM), fourier-transform infrared spectroscopy (FTIR), pyrolysis-gas c hromatography (GC)-mass spectroscopy (MS), microhardness measurements, gas permeability, and solvent permeability measurements. From deposit ion rate data, a reaction mechanism and key reaction parameters were i dentified. The deposition rate of shell membrane material was found to be a diffusion limited reaction of IPC through the forming membrane t o the exterior shell interface (which is believed to be the reaction f ront). The final thickness of the film deposited at the interface and the rate of deposition were found to be strong functions of the IPC co ncentration and oil phase solvent. Films made with diethyl phthalate ( DEP) were thinner and harder than films made using 1,6-dichlorohexane (DCH) as a solvent. Differences in solubility of the forming membrane in DCH and DEP appear to be able to account for the differences in dep osition rate and the hardness (related to cross-linking density). The deposition can be thought of as a phase separation which is affected b y both the poly(electrolyte)/ionomer transition and the amount of cros s-linking. Finally, it was found that the choice of oil phase solvent profoundly affects the evolution of the outer surface roughness.