Thermodynamics of monolayer transfer in the Langmuir-Blodgett method.

Abstract

Thermodynamics of the monolayer transfer from water onto a solid substrate was theoretically investigated in order to understand the transfer mechanism of Langmuir-Blodgett (LB) films. Four elementary processes were introduced as variations in the interface states accompanying the infinitesimal displacement of the three-phase contact line. Each process was made to correspond to monolayer transfer or nontransfer. Free-energy variations in these processes were expressed by the surface or interface energy. The expression for the contact angle was given as functions of the monolayer surface pressure and of the substrate hydrophilicity. The monolayer-transfer characteristics for quasistatic transfer processes were investigated, and limits on monolayer transfer were also given in terms of the monolayer surface pressure and the substrate hydrophilicity. These theoretical results were found to be consistent with the experimental results for stearyl alcohol and Cd stearate LB films on hydrophilic and hydrophobic ${\mathrm{SiO}}_{2}$/Si substrates.