In this paper, we propose several models that describe the dynamics of liquid films
which are covered by a high concentration layer of insoluble surfactant. First, we
briefly review the “classical” hydrodynamic form of the coupled evolution equations
for the film height and surfactant concentration that are well established for small
concentrations. Then we re-formulate the basic model as a gradient dynamics based
on an underlying free energy functional that accounts for wettability and capillarity.
Based on this re-formulation in the framework of nonequilibrium thermodynamics,
we propose extensions of the basic hydrodynamic model that account for (i) nonlinear
equations of state, (ii) surfactant-dependent wettability, (iii) surfactant phase transitions,
and (iv) substrate-mediated condensation. In passing, we discuss important
differences to most of the models found in the literature.
History
School
Science
Department
Mathematical Sciences
Citation
THIELE, U., ARCHER, A.J. and PLAPP, M., 2012. Thermodynamically consistent description of the hydrodynamics of free surfaces covered by insoluble surfactants of high concentration. Physics of Fluids, 24 (10), 102107, 19pp.