Directed vesicle transport by diffusio-osmosis
Institute of Physics, University of Amsterdam - P.O. Box 94485, 1090 GL Amsterdam, The Netherlands
Received: 1 February 2015
Accepted: 12 April 2015
We present a study on surfactant vesicles that spontaneously move towards an oil droplet that is deposited on a glass substrate. Tracer particles in the surfactant solution show that the motion is not self-propelled: the vesicles are entrained by a macroscopic hydrodynamic flow. Measurements of the flow velocity suggest that the flow is of diffusio-osmotic nature. The surfactant is observed to move into the oil phase which creates a gradient in ion concentration in the vicinity of the droplet. As the diffusion coefficients of the surfactant's co- and counter-ions differ, a charge separation takes place and an electric field arises. This electric field then generates a hydrodynamic flow along the charged glass substrate in which the vesicles are entrained.
PACS: 82.70.Uv – Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions) / 82.39.Wj – Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes / 47.61.-k – Micro- and nano- scale flow phenomena
© EPLA, 2015