Interaction Between an Anionic and an Amphoteric Surfactant. Part II: Precipitation

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.

Interaction Between an Anionic and an Amphoteric Surfactant. Part I: Monomer–Micelle Equilibrium

“…One could have defined standard states to avoid the Debye-Hückel correction factor. But in Part II of this series [27], we use the solubility product, K SP ; and unlike K a ; its value would depend on standard states, so we use the classically defined ones here so that the numerical value of K SP will have the same basis as is common in the literature.…”

“…17, 18, 21-23, 35-40, and 44 simultaneously. In part II of this series of papers [27], this information will be combined with solubility product relationships to generate precipitation phase diagrams for DDAO/SDS mixtures, the practical result which is the incentive behind this line of inquiry.…”

“…In Part II of this series [27], we utilize the model developed here to predict precipitation phase boundaries for this system and compare to experimental phase boundaries.…”

The interaction of long chain sodium carboxylates and sodium dodecylsulfate with lead(II) ions in aqueous solutions

“…Over the last decades, there have been a considerable number of scientific reports regarding the interaction between mono-or higher valent ions and ionic surfactants, with particular attention to the phase separation which occurs in these systems [9][10][11]. Precipitation of surfactants, as metal salts, can be desirable in some applications (e.g., catalysis [12] and wastewater treatment [13,14]) but can be also detrimental in others, including detergency, and enhanced oil recovery, due to loss of surfactant activity [15].…”

Spontaneous Emulsification of Triolein Induced by Mixed Micellar Solutions of Sodium Polyoxyethylene Alkyl Ether Sulfate and Dodecyldimethyl Amine Oxide

“…On the other hand, alkyldimethyl amine oxide AO is an amphoteric surfactant. In aqueous solution, AO exists as a mixture comprising protonated hydroxyl amine cationic AO and deprotonated amine oxide nonionic AO species; their relative amounts depend on the pH of the aqueous solution 21,22 . Industrially, AO surfactants are used as foam boosters and for the production of soaps that are mild to the skin 23,24 .…”