Preparation and organized assembly of nanoparticulate TiO2-stearate alternating Langmuir-Blodgett films

Nanoparticulate TiO2-stearate Langmuir-Blodgett-type monolayers and multilayers were directly obtained by using TiO2 hydrosol as the subphase. The surface pressure-versus-surface area isotherms showed that the monolayer could be compressed to a mean molecular area of 0.25 nm(2). The monolayer was transferred onto a CaF2 or Si substrate at a dipping speed of 18 cm/min and surface pressure of 25 mN/m. It exhibited Y-type multilayer films over the range investigated (1-30 layers) with a transfer ratio of 1.0 +/- 0.1. FTIR transmission spectra and linear infrared dichroic spectra provided evidence of the formation of a stable organic/ inorganic alternating multilayer with nanoparticulate TiO2 between the organic monolayers. There is only slight absorption in the range of the C double bond O stretching vibration band of the carboxylic group with the 3- and 6-nm TiO2 nanoparticles. This means that TiO2 particles are packed closely; i.e., the surface coverage is very high. A possible structure consists of layers of nanoparticles in close-packed form with two stearate ion layers in between. But it can be seen that there are some carboxylic groups (1700 cm(-1)) not connected to the 20-nm TiO2 nanoparticle. Electron microscopic (TEM) images of TiO2-stearate monolayers show that high-coverage monolayers were obtained when the surface pressure increased to 25 mN/m and the dipping speed to 18 cm/min. (C) 1997 Academic Press.