We consider the computation of the interfacial properties of molecular chains from direct simulation
of the vapor-liquid interface. The molecules are modeled as fully flexible chains formed from
tangentially bonded monomers with truncated Lennard-Jones interactions. Four different model
systems comprising of 4, 8, 12, and 16 monomers per molecule are considered. The simulations are
performed in the canonical ensemble, and the vapor-liquid interfacial tension is evaluated using the
test area and the wandering interface methods. In addition to the surface tension, we also obtain
density profiles, coexistence densities, critical temperature and density, and interfacial thickness as
functions of temperature, paying particular attention to the effect of the chain length on these
properties. According to our results, the main effect of increasing the chain length at fixed
temperature is to sharpen the vapor-liquid interface and to increase the width of the biphasic
coexistence region. As a result, the interfacial thickness decreases and the surface tension increases
as the molecular chains get longer. The interfacial thickness and surface tension appear to exhibit an
asymptotic limiting behavior for long chains. A similar behavior is also observed for the coexistence
densities and critical properties. Our simulation results indicate that the asymptotic regime is
reached for Lennard-Jones chains formed from eight monomer segments. We also include a
preliminary study on the effect of the cutoff distance on the interfacial properties. Our results
indicate that all of the properties exhibit a dependence with the distance at which the interactions are
truncated, though the relative effect varies from one property to the other. The interfacial thickness
and, more particularly, the interfacial tension are found to be strongly dependent on the particular
choice of cutoff, whereas the density profiles and coexistence densities are, in general, less sensitive
to the truncation.
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