First-order wetting transition and line tension of hexadecane lens at air/water interface assisted by surfactant adsorption

A first-order transition from partial wetting to pseudo-partial wetting of hexadecane droplets on aqueous solutions of surfactant, hexadecyltrimethylammonium bromide, has been investigated by using interfacial tensiometry and ellipsometry. A regular solution model was applied to calculate the surface free energy of the wetting film as a function of thickness and then the connection between calculated surface free energy profiles and line tension measured at the wetting transition was discussed based on the interface displacement model. The reversal of the sign of the line tension associated with the wetting transition was confirmed from both the experiment and the interface displacement model.