| Abstract
| - This work investigates the synergistic effects of a neutral polymer and an anionic surfactant on depletion forcesas a function of bulk polymer and bulk surfactant concentration. In this work, we measure the force between a silicaparticle and a silica plate in aqueous solutions of the polymer and the surfactant using atomic force microscopy. Thepolymer 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 andthe silica plate is primarily repulsive for polymer concentrations ranging from 200 to 10 000 ppm. In SDS-onlysolutions, the net force between the silica surfaces is repulsive at all separations for concentrations below 16 mM SDSand is attractive with a structural force character above 16 mM SDS. When both F108 and SDS are present in thesolution, a net attractive force is observed at SDS concentrations as low as 4 mM, a factor of 2 below the criticalmicelle concentration (cmc). We attribute this synergistic effect to the complexation of F108 with SDS in bulk solutionat a critical aggregation concentration (cac) that is less than the cmc, producing a relatively large, charged complexthat creates a significant depletion force between the particle and plate.
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