Role of n-octadecylacetoacetate as an amphiphilic chelating agent in the two-dimensional sol-gel synthesis of ultrathin films of titania and zirconia

The amphiphilic chelating agent, n-octadecylacetoacetate (C(18)AA), plays a significant role in the two-dimensional sol-gel synthesis of titania and z irconia ultrathin films in improving the stability of the gel films floatin g on water surface and their deposition on a substrate by a Langmuir-Blodge tt (LB) technique. The origin of the improvement effect of C(18)AA was inve stigated in detail by measurements of surface pressure-area isotherms and a rea-time curves as well as by IR and UV spectroscopy. C(18)AA molecules com plex with the metal center of the gel film, and the resulting C(18)AA-stabi lized gel film became stabilized owing the well-balanced. The effect of C(1 8)AA depends on the molar mixing ratio of metal butoxide/C(18)AA, x. In bot h the titania and zirconia systems, the quantitative LB deposition was poss ible when the x value was less than or equal to 3 and the amount of the gel transferred per one deposition became largest at x = 3. The x-dependence w as satisfactorily explained from the relative amounts of the C(18)AA monola yer, C(18)AA-stabilized gel film and C(18)AA-free gel film on the water sur face. The C(18)AA-stabilized gel films with x less than or equal to 3 depos ited on substrates could be converted into the ultrathin oxide films of tit ania and zirconia by heating in air at 773 K for 0.5 h, and the thickness o f the resulting oxide films was controllable in the range of sub-nanometer level not only by the number of deposition but also by the x value.