Post date: Apr 12, 2017 8:07:26 AM
Alexia (master student) and Laurent's paper on Alexia's results has just been accepted in Soft Matter!
Electro-osmosis (EO) is a powerful tool to manipulate liquids in micro and nanofluidic systems. While EO has been studied extensively at liquid-solid interfaces, the case of liquid-vapor interfaces, found e.g. in foam films and bubbles, remains to be explored. Here we performed molecular dynamics (MD) simulations of EO in a film of aqueous electrolyte covered with fluid layers of ionic surfactants and surrounded by gas. Following the experimental procedure, we computed the zeta potential from the EO velocity, defined as the velocity difference between the middle of the liquid film and the surrounding gas. We showed that the zeta potential can be smaller or larger than existing predictions depending on the surfactant coverage. We explained the failure of previous descriptions by the fact that surfactants and bound ions move as rigid bodies and do not transmit the electric driving force to the liquid locally. Considering the reciprocal streaming current effect, we then developed an extended model, which can be used to predict the experimental zeta potential of surfactant-laden liquid-gas interfaces.