Molecular Dynamics Study of Wetting and Adsorption of Binary Mixtures of the Lennard-Jones Truncated and Shifted Fluid on a Planar Wall

The wetting of surfaces
is strongly influenced by adsorbate layers.
Therefore, in this work, sessile drops and their interaction with
adsorbate layers on surfaces were investigated by molecular dynamics
simulations. Binary fluid model mixtures were considered. The two
components of the fluid mixture have the same pure component parameters,
but one component has a stronger and the other a weaker affinity to
the surface. Furthermore, the unlike interactions between both components
were varied. All interactions were described by the Lennard-Jones
truncated and shifted potential with a cutoff radius of 2.5σ.
The simulations were carried out at constant temperature for mixtures
of different compositions. The parameters were varied systematically
and chosen such that cases with partial wetting as well as cases with
total wetting were obtained and the relation between the varied molecular
parameters and the phenomenological behavior was elucidated. Data
on the contact angle as well as on the mole fraction and thickness
of the adsorbate layer were obtained, accompanied by information on
liquid and gaseous bulk phases and the corresponding phase equilibrium.
Also, the influence of the adsorbate layer on the wetting was studied:
for a sufficiently thick adsorbate layer, the wall’s influence
on the wetting vanishes, which is then only determined by the adsorbate
layer.