Nanoscale Wettability of Water-Alcohol Mixtures on Graphite Surface: Molecular Dynamics Study

The ability to predict and control surface wettability at the nanoscale is crucial and rapidly evolving, particularly in the fields of microfluidics and nanotechnology. Typically, the contact angle is measured in simulations by creating a liquid droplet on a solid surface, fitting a curve to the droplet’s interface, and determining the angle at the triple-phase contact line. However, at the molecular level, the triple-phase contact line becomes ambiguous due to the continuous motion of molecules, making conventional measurements difficult. This study reports the molecular dynamics simulations to determine the contact angle of water mixed with four primary alcohols (RN-OH, where R = (CNH2N+1), N varies from 1 to 4) on a graphite substrate, using the Hautman and Klein method, which links the microscopic contact angle to the droplet’s average center of mass height through the concepts of equivalent contact area and volume. The water concentration is varied from 50% to 90% in the alcohol mixture. ContactAngleCalculator code is modified to calculate the contact angle of binary liquids. Results show that increasing alcohol concentration leads to greater spreading.