Wettability analysis was used as a simple method to characterize the surface conditions of Langmuir-Blodgett (LB) films. Monolayers of stearic acid (SA) on air/liquid interface were investigated first and then, transferred to a hydrophilic glass surface to prepare LB film of one monolayer. The uniformity, stability and molecular orientation of the LB films were studied by the measurement of dynamic contact angle (Wilhelmy plate method) and compared with the information inspected by the atomic force microscopy. The results show that the SA monolayer is more stable on CdCl 2 solution than that on the pure water. The transfer ratio for the deposition of LB film was close to unity at low surface pressures, but it increases to a value larger than 2 at higher surface pressures (30, 40 mN/m) as a result of significant collapse effect. For one layer of SA films obtained at low surface pressures, the advancing contact angles (114°) were equivalent to the θ a of a methyl-terminated monolayer, but the receding contact angle (23°) is much smaller than the θ r of the methyl-terminated surface (about 90°), which reflects that the LB films are not homogeneous but contain a significant area ratio of hydrophilic region. When the transfer is operated at high surface pressure, the advancing contact angle decreases obviously. This phenomenon is attributed to the significant collapse effects on the monolayer, which lead to the formation of multiplayer or aggregative structure and thus, the area ratio of the hydrophobic tail of SA is decreased. Due to the small attractive force of the hydrophilic pole of SA to the glass surface, the SA LB film is not stable during the analysis of dynamic contact angle (DCA). The surface condition estimated from the surface wettability is consistent with the results inspected by AFM.
|Number of pages||8|
|Journal||Journal of the Chinese Institute of Chemical Engineers|
|Publication status||Published - 2001 Sep 1|
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)