Interaction Between an Anionic and an Amphoteric Surfactant. Part II: Precipitation |
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| Authors: | Sukhwan Soontravanich Sarah Walsh John F. Scamehorn Jeffrey H. Harwell David A. Sabatini |
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| Affiliation: | (1) Institute for Applied Surfactant Research, University of Oklahoma, 100 E Boyd St., Rm. T-335, Norman, OK 73019, USA |
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| Abstract: | Use of amphoteric and anionic surfactants is very common in practical formulations such as shampoos and hand dishwashing products. Precipitation of mixtures of dimethyldodecylamine oxide (DDAO) as an amphoteric surfactant and sodium dodecyl sulfate (SDS) as an anionic surfactant were studied at different pH levels. The DDAO is a pH-sensitive surfactant and its protonation can be expressed in terms of a pK a similar to an acid dissociation constant. The protonated form of DDAO carries a positive charge and precipitates with the oppositely charged SDS. Therefore, precipitation phase boundaries are pH dependent due to the varying degree of DDAO protonation. By combining the use of regular solution theory and the pseudophase separation model to describe micellar mixing nonidealities with the precipitate solubility product constant and the protonation dissociation constant, a model to predict the precipitation phase boundary is presented here. The model agrees well with experimental phase boundaries at different pH levels. |
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| Keywords: | Anionic surfactants Application of surfactants Cationic surfactants Detergent formulation Interfacial science Nonionic surfactants Surface activity |
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