Molecular
dynamics simulations were carried out to investigate
cylindrical droplets consisting of binary mixtures of Lennard-Jones
(LJ) fluids in contact with a solid substrate. The droplets are composed
of mixtures of the monomeric LJ fluid plus linear-tangent chains of
2, 10, 20, and 30 segments per chain that interact through a harmonic
potential and the spherically truncated and shifted potential Lennard-Jones.
The solid surface was modeled as a semi-infinite platinum substrate
with an FCC structure that interacts with the fluid by means of a
LJ 9-3 potential. We place emphasis on the effect of mixing a monomeric
LJ fluid with heavy components on the contact angle and on the droplet
structure, especially in the liquid–solid region. The density
profiles of the droplets reveal a strong discrete layering of the
fluid in the vicinity of the solid–liquid interface. The layering
is more pronounced at low temperatures and for mixtures of short chains
(symmetric mixtures). The ordering of the fluid was much less intense
for fluids of long chains (asymmetric mixtures), and some cases even
show gas enrichment at the solid–liquid interface. Enrichment
at the vapor–liquid interfaces and density inversion can also
be observed. However, these effects are not as marked as in planar
interfaces. The contact angle between the droplet and the substrate
is calculated by fitting an ellipse to the vapor–liquid interface
defined by the Gibbs dividing surface. In general, an increment in
the concentration of the heavy component and a reduction of the temperature
resulted in an increase of the contact angle, which in turn disfavored
the wetting of the droplet.