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Interaction Between an Anionic and an Amphoteric Surfactant. Part II: Precipitation
Author(s) -
Soontravanich Sukhwan,
Walsh Sarah,
Scamehorn John F.,
Harwell Jeffrey H.,
Sabatini David A.
Publication year - 2009
Publication title -
journal of surfactants and detergents
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.349
H-Index - 48
eISSN - 1558-9293
pISSN - 1097-3958
DOI - 10.1007/s11743-009-1106-x
Subject(s) - chemistry , protonation , pulmonary surfactant , solubility , inorganic chemistry , solubility equilibrium , precipitation , dissociation constant , dissociation (chemistry) , sodium dodecyl sulfate , phase (matter) , acid dissociation constant , aqueous solution , chromatography , organic chemistry , ion , biochemistry , physics , receptor , meteorology
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 p K 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.