Viscosities of O/W Emulsions Stabilized by Nonionic Surfactants. I. Characteristics of Nonionic Surfactants in Emulsion Viscosities

Abstract

Abstract O/W emulsions of mineral oil were prepared, using several types of nonionic surfactants, and their relative viscosities were measured with a rotating-cup viscometer, together with microscopic and visual observation of the emulsions. It was found that there are two maxima in the curve of the relative viscosity vs. the ratio of the two surfactants in the mixed emulsifier employed. From these figures, the relative effects of the nonionic surfactants on the emulsion viscosities were discussed. It was confirmed that the emulsion viscosity at the optimum composition decreases in the following order: for sorbitan fatty acid esters, SMS>SMP>SML>SMO>SSO>STS for polyoxyethylene sorbitan fatty acid esters, E–SMS–20>E–SMP–20>E–SMO–20>E–SML–20 for glyceryl monostearates, GMS–IV>GMS–III>>GMS–V>GMS–II>GMS–I For the other types the order of the series was not distinct. In the former two series, the orders of the arrangements are parallel with those of the decreasing carbon atom numbers in the molecule in the case of saturated fatty acid derivatives. The soap effect is considered to appear in the case of glyceryl monostearates, the so-called self-emulsifying types of the emulsifier. Using the scale of viscosity vs. virtual HLB value, we can determine by means of emulsification the most probable HLB value of the nonionic surfactants. Good agreements are seen between the HLB values determined by viscosity minimum and those determined by the emulsification test reported on in the preceding paper.