title: Negative adsorption due to electrostatic exclusion of micelles.
abstract: Interactions of surfactants with solid substrates are important in the controlling of processes such as flotation, coating, flocculation and sedimentation. These interactions usually lead to adsorption on solids, but can also result in an exclusion of the reagents with dire consequences. In this work electrostatic exclusion of negatively charged dodecylbenzene sulfonate micelles from quartz/water, Bio-Sil/water and alumina/water interfaces has been investigated as a function of pH and ionic strength. Measurable negative adsorption of these surfactants from similarly charged solid/liquid interface was observed in the micellar region. In the case of porous samples with large surface area, comparison of pore size with the micelle size is necessary to avoid any erroneous conclusions regarding the role of electrostatic exclusion in a given system. A theoretical model for the electrostatic exclusion of micelles is developed and used to calculate the adsorption of negatively charged dodecylbenzene sulfonate on negatively charged quartz (pH 7), silica (Bio-Sil A, pH 3) and alumina (pH 11) in the micellar concentration region. The micellar exclusion values calculated using the model are in excellent agreement with the experimental results.
authors.affiliation: NSF IUCR Center for Advanced Studies in Novel Surfactants, Langmuir Center for Colloid and Interfaces, Columbia University, New York, NY 10027, USA. ps24@columbia.edu
authors.forename: P
authors.initials: P
authors.lastname: Somasundaran
authors.forename: K P
authors.initials: KP
authors.lastname: Ananthapadmanabhan
authors.forename: Puspendu
authors.initials: P
authors.lastname: Deo
mesh_terms: D000327:Adsorption; D000537:Aluminum Oxide / Q000737:chemistry; D001557:Benzenesulfonates / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008823:Micelles; D009994:Osmolar Concentration; D011791:Quartz / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D055672:Static Electricity; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D001557:Benzenesulfonates; D008823:Micelles; D014867:Water; D011791:Quartz; D012965:Sodium Chloride; C001114:dodecylbenzenesulfonic acid; D000537:Aluminum Oxide