title: Synergistic effects of polymers and surfactants on depletion forces.
abstract: This work investigates the synergistic effects of a neutral polymer and an anionic surfactant on depletion forces as a function of bulk polymer and bulk surfactant concentration. In this work, we measure the force between a silica particle and a silica plate in aqueous solutions of the polymer and the surfactant using atomic force microscopy. The polymer is the triblock copolymer poly(ethylene oxide-block-propylene oxide-block-ethylene oxide) (Pluronic F108), and the surfactant is sodium dodecyl sulfate (SDS). In F108-only solutions, the force between the silica particle and the silica plate is primarily repulsive for polymer concentrations ranging from 200 to 10 000 ppm. In SDS-only solutions, the net force between the silica surfaces is repulsive at all separations for concentrations below 16 mM SDS and is attractive with a structural force character above 16 mM SDS. When both F108 and SDS are present in the solution, a net attractive force is observed at SDS concentrations as low as 4 mM, a factor of 2 below the critical micelle concentration (cmc). We attribute this synergistic effect to the complexation of F108 with SDS in bulk solution at a critical aggregation concentration (cac) that is less than the cmc, producing a relatively large, charged complex that creates a significant depletion force between the particle and plate.
authors.affiliation: Department of Chemical Engineering, Yale University, New Haven, Connecticut 06520-8286, USA.
authors.forename: Aysen
authors.initials: A
authors.lastname: Tulpar
authors.forename: Robert D
authors.initials: RD
authors.lastname: Tilton
authors.forename: John Y
authors.initials: JY
authors.lastname: Walz
mesh_terms: D000838:Anions / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods*; D004573:Electrolytes; D008823:Micelles; D018625:Microscopy, Atomic Force; D008956:Models, Chemical; D015233:Models, Statistical; D008970:Molecular Weight; D053758:Nanoparticles / Q000737:chemistry*; D020442:Poloxamer / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D012822:Silicon Dioxide; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D000838:Anions; D004573:Electrolytes; D008823:Micelles; D011108:Polymers; D013501:Surface-Active Agents; D020442:Poloxamer; D012967:Sodium Dodecyl Sulfate; D012822:Silicon Dioxide