Welcoming Remarks

When an organic fatty acid solution of palmitic acid in tetradecane is brought into contact with an aqueous solution of the cationic surfactant tetradecyltrimethylammonium bromide, spontaneous convective motion is observed at the interface. Ripple-like bursting patterns are sustained for a duration which increases with the concentration of surfactant, eventually ceasing at long times. The solubility of each surfactant is negligible in the other phase, ruling out the solute transfer across the interface which
typically drives Bénard–Marangoni convection. A linear stability analysis also rules out the possibility of an instability driven solely by dynamic adsorption of surfactant to the interface, since the stabilizing stresses of surface advection predominate. For a sufficient pH in the aqueous phase, the fatty acid is known to ionize at the interface. Therefore, an association reaction is hypothesized between the oppositely charged surfactants at the interface, leading to formation of complexes which desorb into the
aqueous phase and cause turbidity in the bulk. A linear stability analysis is then formulated for a system combining dynamic adsorption of two surfactants with an association reaction at the interface, finding that a reaction can profoundly destabilize the system. Direct numerical simulations of the convective instability reveal wavelike patterns and the crucial role of low adsorbed concentrations in enabling the instability.