Anionic-nonionic surfactant mixture to attain emulsion insensitivity to temperature

Abstract

It is well known that anionic surfactants become more hydrophilic as temperature increases, whereas nonionic surfactants show the opposite trend. By a proper mixing of both types of surfactants it is possible to produce intermediate situations and, eventually, insensitivity to temperature. This mixing principle is applied to both the phase behavior and emulsion properties.The temperature/water-to-oil ratio phase diagram is mapped for different mixtures of an alkyl aryl sulfonate and an ethoxylated alkyl phenol. The experimental evidence indicates that there is a continuous variation from the case 100% of anionic to 100% nonionic. The three-phase zone behaves as a rotating band which finally flips upside down.The emulsion inversion line undergoes a transition, with an anionic-nonionic intermediate mixture exhibiting an inversion line independent of the temperature. For this anionic-nonionic mixture, the three-phase behavior region is an extremely extended band, and it is associated with an “abnormal” emulsion type all over the temperature and composition range. These emulsions are extremely unstable.