title: Multilayering of Calcium Aerosol-OT at the Mica/Water Interface Studied with Neutron Reflection: Formation of a Condensed Lamellar Phase at the CMC.
abstract: Using specular neutron reflection, the adsorption of sodium and calcium salts of the surfactant bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT or AOT) has been studied at the mica/water interface at concentrations between 0.1 and 2 CMC. The pH dependence of the adsorption was also probed. No evidence of the adsorption of Na(AOT) was found even at the critical micelle concentration (CMC) while the calcium salt was found to adsorb significantly at concentrations of 0.5 CMC and above. This interesting and somewhat unexpected finding demonstrates that counterion identity may be used to tune the adsorption of anionic surfactants on anionic surfaces. At the CMC, three condensed bilayers of Ca(AOT)2were adsorbed at pH 7 and 9 and four bilayers adsorbed at pH 4. Multilayering at the CMC of Ca(AOT)2on the mica surface is an unusual feature of this surfactant/surface combination. Only single bilayer adsorption has been observed at other surfaces at the CMC. We suggest this arises from the high charge density of mica which must provide an excellent template for the surfactant.
authors.affiliation: BP Institute and Department of Chemistry, University of Cambridge , Cambridge CB3 0EZ, U.K.
authors.forename: L R
authors.initials: LR
authors.lastname: Griffin
authors.affiliation: BP Institute and Department of Chemistry, University of Cambridge , Cambridge CB3 0EZ, U.K.
authors.forename: K L
authors.initials: KL
authors.lastname: Browning
authors.affiliation: BP Institute and Department of Chemistry, University of Cambridge , Cambridge CB3 0EZ, U.K.
authors.forename: S Y
authors.initials: SY
authors.lastname: Lee
authors.affiliation: ISIS Facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory , Didcot, Oxfordshire OX11 0QX, U.K.
authors.forename: M W A
authors.initials: MW
authors.lastname: Skoda
authors.affiliation: ISIS Facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory , Didcot, Oxfordshire OX11 0QX, U.K.
authors.forename: S
authors.initials: S
authors.lastname: Rogers
authors.affiliation: BP Institute and Department of Chemistry, University of Cambridge , Cambridge CB3 0EZ, U.K.
authors.forename: S M
authors.initials: SM
authors.lastname: Clarke