  Accurate estimation of surface wettability for various degrees of
hydrophobicity becomes increasingly important in the molecular design of
membrane. In this paper, we develop simple yet physically realistic model for
estimating contact angle via hybridizing molecular dynamics and pseudocontinuum
theory. Molecular dynamics simulations were carried out to compute the
macro-scale contact angle between a water droplet and smooth walls from the
nanoscale calculations. A macro-level droplet including countless degrees of
freedom due to an infinite number of molecules is impossible to be studied
directly via atomistic simulations. To resolve this issue, we employed two
approaches consisting of the pseudocontinuum approximation and the modified
Young-Laplace equation. The former involves the 9-3 Lennard-Jones (L-J)
potential and can drastically reduce the degrees of freedom in molecular
simulations, while the latter relates the mesoscale contact angle to the
realistic one. We altered different parameters including the liquid-surface
potential characteristics and the temperature, and calculated the water contact
angle by leveraging the mass density profile fitting method to predict the
broad spectrum of hydrophobic and hydrophilic substrates. The computational
results were compared with the experimental data for various materials
including graphite, silicon, and metals. This study suggests that
pseudocontinuum modeling is an accurate approach to probe surface wettability
for various processes at a low computational cost.
