Dynamics of deposition of Langmuir-Blodgett multilayers

The process of Langmuir-Blodgett deposition is considered from the view-point of (de)wetting dynamics. Two models for the description of the dependence of the dynamic contact angle during deposition on the three-phase contact-line velocity are considered: a purely hydrodynamic model and a combined molecular-hydrodynamic one. The latter takes into account both viscous dissipation and the 'molecular-kinetic' type of dissipation caused by adsorption in the immediate vicinity of the moving contact line. Comparison with the available experimental data shows that the combined model satisfactorily describes the dependence of the receding dynamic angle on the contact-line velocity, whereas the purely hydrodynamic model alone fails in this respect. The analysis of the energy dissipated during the contact-line motion shows that, in the systems under consideration, the motion of the contact line is hindered mainly by the 'molecular-kinetic' type of friction whereas viscous drag becomes important at small values of the dynamic contact angle, i.e. when the contact-line velocity is close to the critical velocity of liquid film entrainment.