The adsorption of dodecyltrimelhylammonium bromide on mica in aqueous solution studied by X-ray diffraction and atomic force microscopy

The adsorption of dodecyltrimethylammonium bromide (DTAB) onto natural musc ovite mica and a synthetic expandable mica (EM) in aqueous solution has bee n investigated using both microscopic and macroscopic surface characterizat ion techniques. The electrokinetic properties of the surfaces were monitore d as a function of the concentration of DTAB using atomic force microscopy and microelectrophoresis. The adsorption isotherm of DTAB on EM was measure d up to a solution concentration just below the critical micelle concentrat ion of the surfactant, The thickness of the adsorbed layer on EM was determ ined using X-ray diffraction. Results indicate that the adsorbed layer cons ists of molecules lying quite flat on the mica surface at low concentration s and adsorbed in interleaved aggregate structures at concentrations approa ching the critical micelle concentration of the surfactant in solution. (C) 2001 Academic Press.