Structure of high-internal-phase-ratio emulsions

The structure of high-internal-phase-ratio emulsions was treated, theoretically and mathematically, in a paper presented at the National Colloid Symposium in 1966 (1). At that time, certain postulates were proposed to explain the rheological properties of these emulsions on the basis of the geometry of the particle packing. Certain predictions were made concerning behavior in the 94-96% internal phase region, These predictions have since been confirmed by independent investigators (2). Attempts were made at several laboratories to obtain photographs of the emulsion structure using conventional light microscopy and phase-contrast microscopy. None of these attempts were particularly successful, since the structure was distorted by the slide making process. Since then, it has become possible to freeze the structure of these emulsions by polymerizing one of the phases and taking scanning electron photomicrographs. In the first series of studies made using this technique (3), a high-internal-phase-ratio emulsion of water in resin was made and the resin external phase was polymerized. The block of polymer was then broken and SEM pictures made of the internal structure. In this series of studies, we are using a polymerizable internal phase, vinyl chloride, and making oil in water emulsions. The effects of phase ratio, catalyst ratio, and preparation method were studied. In addition to the SEM photographs, the molecular weight distribution of the polymers was determined by gel permeation chromatography and intrinsic viscosity measurements.