Effects of dodecanol on the adsorption kinetics of SDS at the water–hexane interface

• Published in: Journal of colloid and interface science Vol. 351; no. 2; pp. 537 - 541
• Main Authors: Javadi, A., Mucic, N., Vollhardt, D., Fainerman, V.B., Miller, R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 15.11.2010; Elsevier
• Subjects: Adsorption; Adsorption kinetics; Chemistry; Dodecanol; Dodecanol - chemistry; Dodecanol effects; Droplets; Dynamics; Exact sciences and technology; General and physical chemistry; Hexanes; Hexanes - chemistry; Kinetics; Mathematical models; Oil/water interface; Sodium Dodecyl Sulfate - chemistry; Sodium dodecyl sulphate (SDS); Surface chemistry; Surface physical chemistry; Surface Properties; Surface-Active Agents - chemistry; Surfactants; Tensiometry; Water - chemistry; Sodium dodecyl sulphate (SDS); Oil/water interface; Dodecanol effects; Adsorption kinetics; Tensiometry; Water; Impurity; Interface tension; Dynamic properties; Surfactant; Ionic surfactant; Dynamics; Hexane; Diffusion; Surface activity; Concentrated solution; Solubility; Droplet; Lauryl sulfate; Hydrolysis; Anionic surfactant; Liquid; Oil; Adsorption; Sodium; Distribution; Isotherm; Models; Kinetics; Aqueous solution; Physicochemical properties; Interface
• ISSN: 0021-9797; 1095-7103; 1095-7103
• DOI: 10.1016/j.jcis.2010.07.033

It is demonstrated in this paper that the “natural” impurity C12OH (dodecanol) does not remarkably affect the adsorption dynamics of SDS at the water/hexane interface. However complementary experiments via direct admixture dodecanol in hexane indicate a significant decrease in interfacial tension of the water–hexane interface at concentrations higher than 10 −3 mol/l in hexane. This condition may happen when the oil phase is distributed as a small droplet in a high concentrated solution of SDS. Dynamic surface/interfacial tension of C12OH solution 10 −5 (1) and 2 × 10 −5 (2) mol/l in water against air, and C12OH solution 2 × 10 −5 (3), 10 −3 (4), 10 −2 (5) and 10 −1 (6) mol/l in hexane against water, and aqueous phase of C12OH obtained from saturated with 10 −1 mol/l C12OH in hexane, also measured against air (7). [Display omitted] ► The “natural” impurity C12OH (dodecanol) in sodium dodecyl sulphate (SDS) solutions have much less effects on the water–oil interfaces in comparison with water–air interface. ► Complementary experiments via direct admixture of dodecanol in hexane indicate negligible effects on interfacial tension at the water–hexane interface for concentrations up to 10 −3 mol/l in hexane. ► However for higher concentration significant effects appear. This condition may happen when the oil phase is formed as a small droplet in a high concentrated solution of SDS. Even though sodium dodecyl sulphate (SDS) is the most frequently studied surfactant, its properties at liquid interfaces are not easily accessible. This is mainly caused by the fact that in aqueous solution SDS is subject to hydrolysis, by which the homologous dodecanol (C12OH) is formed. Due to its enormously high surface activity it competes with SDS at the interface. We demonstrate here that this “natural” impurity C12OH does not remarkably affect the adsorption dynamics of SDS at the water/hexane interface, due to its high solubility in hexane. Therefore, the dynamic adsorption properties can be determined independent of disturbing dodecanol effects. The surfactant adsorbs diffusion controlled and the interfacial tension isotherm at the water/hexane interface is well described by a Frumkin model. However complementary experiments via direct admixture of dodecanol in hexane indicate a significant decrease in interfacial tension of the water–hexane interface at concentrations higher than 10 −3 mol/l in hexane. This condition may happen when the oil phase is distributed as small droplets in a high concentrated solution of SDS. The distribution coefficient of C12OH between water and hexane is estimated from adsorption experiments to be K p = c o / c w = 6.7 × 10 3.