DEPLETION FORCES IN THE PRESENCE OF ELECTROSTATIC DOUBLE-LAYER REPULSION

We report direct measurements of the repulsive force-distance profiles between submicronic colloidal droplets stabilized by an ionic surfact ant in the presence of the same surfactant micelles. We establish that the repulsive force profile may be described by a sum of two contribu tions. One is repulsive and arises from the presence of the droplets' double layers. The other originates in the depletion of charged micell es and is attractive. We conclude that the electrostatic repulsion bet ween the micelles and the droplets enhances the depletion force. This effect is simply accounted for by considering an effective larger drop let diameter. We present the empirical relation between this extra thi ckness and the Debye length.