Effects of tween and span group emulsifiers on the stability of o/w emulsions.

The effect of blending Tween and Span emulsifiers on emulsion formation were investigated, and the HLB values required to produce stable o/w emulsions are considered in detail. The emulsifiers used were the commercial grade Tween series and Span series, and the oil used was a liquid paraffin (dispersed phase). Emulsion stability was measured by four methods : with a measuring cylinder, a Coulter counter, a turbidimeter, and a rheometer. The following results were obtained ; (1) The rate of separation increased in the following order with blended emulsifiers : Tween 80+Span 20, Tween 20+Span 20, Tween 40+Span 20, and Tween 20+Span 80. However, the emulsion prepared with Tween 20+Span 80 was unstable over the whole range of HLB. (2) The o/w emulsions prepared using mixtures of Tween and Span showed a maximum droplet number at an HLB value of 11.0. (3) The viscosity of the emulsion prepared with Tween alone was clearly smaller than those obtained with blended emulsifiers.