Influence of pH on the stability of oil-in-water emulsions stabilized by asplittable surfactant

A laboratory study was conducted to evaluate the effect of pH on the stabil ity of oil-in-water emulsions stabilized by a commercial splittable surffac tant Triton SP-190 by comparison with the results obtained by a common surf actant Triton X-100. The emulsion stability was explored by measuring the v olume of oil phase separated and the size of the dispersed droplets. It was found that the addition of inorganic acids did not significantly affect th e stability of emulsions stabilized by Triton X-100, but had a profound inf luence on the stability of emulsions stabilized by Triton SP-190. Moreover, the droplet size of a Triton X-100-stabilized emulsion and its dynamic int erfacial activity were insensitive to acids. However, at lower pH the dropl et size of the emulsions stabilized by Triton SP-190 was considerably incre ased. From the dynamic interfacial tension measurements the dynamic interfa cial activity of Triton SP-190 at the oil/water interface was found to be s trongly inhibited by the addition of acids, resulting in a slower decreasin g rate of dynamic interfacial tension. The results demonstrate that the dra matic destabilization of Triton SP-190-stabilized emulsions could be realiz ed by the use of acids, which evidently changed the interfacial properties of the surfactant and resulted in a higher coalescence rate of oil droplets . (C) 2000 Elsevier Science B.V. All rights reserved.