HIGH INTERNAL PHASE WATER-IN-OIL EMULSIONS - INFLUENCE OF SURFACTANTS AND COSURFACTANTS ON EMULSION STABILITY AND FOAM QUALITY

The relationship between the hydrophilic-lipophilic balance (HLB) number of a cosurfactant and the stability of a styrene-based emulsion is studied for 8 surfactants and 22 cosurfactants. The amount of cosurfactant that can be incorporated into a water-in-oil emulsion is strongly and inversely coupled to the HLB number of the cosurfactant with a correlation of 96%. The higher the HLB number the smaller the amount of cosurfactant required to form large, coalesced droplets in the emulsion and, hence, in the ultimate polymeric foam. Methanol is an obvious deviant from the typical HLB number-related, cosurfactant disintegration of the sorbitan monooleate containing emulsions. Some modifications to the literature assignments of HLB numbers are recommended. A mechanism is presented for the dual droplet distribution observed for nonionic cosurfactants. The mechanism for the disintegration of emulsions by anionic and nonionic surfactants appears to be different, but the ultimate dependence on HLB number appears to be similar.