Molecular dynamics simulation of nanosized water droplet spreading on chemically heterogeneous surfaces

The wetting kinetics of water droplets on chemically heterogeneous surfaces is important in several industrial technologies, such as biomedicine and microfluidics. Surfaces with different wettabilities can be designed to control the spread of droplets. In this study, nanosized water droplet spreading on chemically heterogeneous surfaces was investigated using molecular dynamics simulations. Chemically heterogeneous surfaces with different wetting patterns were investigated, and the equivalent spreading radius and dynamic contact angle during the spreading process were analyzed. Results showed that droplet spreading is mainly dependent on the area fractions of hydrophobic and hydrophilic regions and the shape of the wetting pattern has a minor influence on the spreading process. The dynamic contact angle can be well predicted by molecular kinetics theory. The static contact angle data remarkably deviate from Cassie’s equation, while they agree better with the modified Cassie’s equation as a function of the hydrophobic length fraction, indicating that the wetting pattern has a substantial influence in the vicinity of the contact line.