title: Structural characterization of surfactant aggregates adsorbed in cylindrical silica nanopores.
abstract: The self-assembly of nonionic surfactants in the cylindrical pores of SBA-15 silica with a pore diameter of 8 nm was studied by small-angle neutron scattering (SANS) at different solvent contrasts. The alkyl ethoxylate surfactants C(10)E(5) and C(12)E(5) exhibit strong aggregative adsorption in the pores as indicated by the sigmoidal shape of the adsorption isotherms. The SANS intensity profiles can be represented by a sum of two terms, one accounting for diffuse scattering from surfactant aggregates in the pores and the other for Bragg scattering from the pore lattice of the silica matrix. The Bragg reflections are analyzed with a form factor model in which the radial density profile of the surfactant in the pore is approximated by a two-step function. Diffuse scattering is represented by a Teubner-Strey-type scattering function which indicates a preferred distance between adsorbed surface aggregates in the pores. Our results suggest that adsorption starts with formation of discrete surface aggregates which increase in number and eventually merge to interconnected patches as the plateau value of the adsorption isotherm is approached. A grossly different behavior, viz. formation of micelles as in solution, is found for the maltoside surfactant C(10)G(2), in agreement with the observed weak adsorption of this surfactant in SBA-15.
authors.affiliation: Institute of Chemistry, Stranski Laboratory, Technical University Berlin, Strasse des 17. Juni 124, 10623 Berlin, Germany.
authors.forename: Tae Gyu
authors.initials: TG
authors.lastname: Shin
authors.forename: Dirk
authors.initials: D
authors.lastname: Müter
authors.forename: Jens
authors.initials: J
authors.lastname: Meissner
authors.forename: Oskar
authors.initials: O
authors.lastname: Paris
authors.forename: Gerhard H
authors.initials: GH
authors.lastname: Findenegg
mesh_terms: D000327:Adsorption; D058608:Nanopores; D033363:Neutron Diffraction; D053838:Scattering, Small Angle; D012822:Silicon Dioxide / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: C509969:SBA-15; D012997:Solvents; D013501:Surface-Active Agents; D012822:Silicon Dioxide