An AFM study of the surface force between TiO₂ surfaces in C_NTACl solutions

Direct surface force measurements have been carried out between titania surfaces in water and in C_nTACl (n = 14, 18) solutions using an Atom Force Microscope (AFM). It was found that the surface potential for rutile is about -50mv. The Hamaker constant A₁₃₁ is 4±1×10 ^-20 J for rutile in water. In C_nTACl (n = 14, 18) surfactant solutions, the force curves show a repulsion/attraction/repulsion transition changing with surfactant concentration. The strongest long range attraction was observed between the TiO₂ surfaces in C _nTACl solutions in the vicinity of respective p.c.n. (point of charge neutralization), which decreases with surfactant chain length increasing. The long-range attractive hydrophobic force was discussed in terms of the charged-patch model of Miklavic et al. (1994) and the model proposed by Eriksson et al. (1989). The discussion sheds light on the origin of the long-range attractions observed between hydrophobic surfaces.