title: Thermodynamics of mixed anionic/nonionic surfactant adsorption on alumina.
abstract: The adsorption of sodium dodecyl sulfate and a polyethoxylated nonylphenol, and well defined mixtures thereof, was measured on gamma-alumina. A pseudo-phase separation model to describe mixed anionic/nonionic admicelle (adsorbed surfactant aggregate) formation was developed, analogous to the pseudo-phase separation model frequently used to describe mixed micelle formation. In this model, regular solution theory was used to describe the anionic/nonionic surfactant interactions in the mixed admicelle and a patch-wise adsorption model was used to describe surfactant adsorption on a heterogeneous solid surface. The formation of mixed anionic/nonionic admicelles in the absence of micelles was accurately described by regular solution theory; mixed admicelle formation exhibited stronger negative deviations from ideality than mixed micelle formation. An adequate description of mixed anionic/nonionic admicelle formation in the presence of mixed micelles was obtained through a simultaneous solution of the pseudo-phase separation models for mixed admicelle and mixed micelle formation, and the appropriate mass balance equations. Anionic/nonionic mixed adsorption in the presence of mixed micelles was shown to correspond to an admicelle composition of approximately a 1:1 anionic/nonionic mole ratio throughout Regions II and III of the adsorption isotherm.
authors: Institute for Applied Surfactant Research and School of Chemical, Biological and Materials Engineering, University of Oklahoma, Sarkey's Energy Center Room T-335, Norman, OK 73019, USA. jeffreylopata@comcast.net
authors: Jeffrey J
authors: JJ
authors: Lopata
authors: Kendall M
authors: KM
authors: Werts
authors: John F
authors: JF
authors: Scamehorn
authors: Jeffrey H
authors: JH
authors: Harwell
authors: Brian P
authors: BP
authors: Grady
mesh_terms: D000327:Adsorption; D000537:Aluminum Oxide / Q000737:chemistry*; D000838:Anions / Q000737:chemistry; D008823:Micelles; D010636:Phenols / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D000838:Anions; D008823:Micelles; D010636:Phenols; D013501:Surface-Active Agents; D012967:Sodium Dodecyl Sulfate; C025256:nonylphenol; D000537:Aluminum Oxide