Surface characterization of octadecylamine films prepared by Langmuir-Blodgett and vacuum deposition methods by dynamic contact angle measurements

The behavior of octadecylamine (ODA) monolayers on various subphases is inv estigated. The monolayer is then transferred to a hydrophilic glass surface to prepare a LB film of one monolayer. The uniformity, stability, and mole cular orientation of the LB films were studied by the measurement of dynami c contact angle and compared with characteristics of vacuum-deposited films . The results show that the ODA monolayer is especially stable on alkaline solution. The LB film transferred from the alkaline solution is stable and uniform in wettability. The advancing and receding contact angles of water on one layer of ODA film are about 113 degrees and 62 degrees, respectively . These values are the same as those on a vacuum-deposited ODA film of equi valent thickness The growth of ODA on a glass surface in a vacuum depositio n is thus found to follow a mode of layer growth. The orientation and arran gement of molecules on the LB films are affected by the surface pressure an d transferring fate during the transferring procedure. When the transfer is proceeded at low surface pressure and high transferring rate, the ODA mole cules are irregularly packed without uniform orientation. However, during t he analysis of dynamic contact angle (DCA), the movement of the three-phase contact line has an effect to rearrange the irregularly packed molecules o f ODA on the LB films and the surface becomes more and more uniform with th e analytic cycles of the DCA, By comparing between the LB films of ODA and stearic acid, the advancing contact angles are identical for both, but the very small value of receding contact angle an stearic acid reflects the exp osure of the hydrophilic glass on the stearic acid film. The existence of h oles in the stearic acid monolayer is thus proved by the measurement of wet tability.