Spreading and adhesion forces for water droplets on methylated glass surfaces

Measurements of the spreading and capillary forces for liquids deposited on solid surfaces of varying surface chemistry and topography are a prerequisite to better understanding and quantification of the wetting mechanisms. In this study, glass slide surfaces were modified with trimethylchlorosilane to fabricate surfaces of varying hydrophobicity. Then, the forces of spreading and adhesion were measured between water droplets and glass surfaces using a high-sensitivity microelectronic balance. Integrated with a digital camera, the experimental set-up recorded forces and water droplet deformations during water droplet attachment, spreading, compression and retraction processes. It was confirmed that the spreading force increases with decreasing advancing contact angle for methylated glass, following a similar correlation as observed for smooth and rough polymers. However, the spreading force values for methylated glass were a few times lower than reported for polymers in spite of a similar roughness characteristic. It was also confirmed that the maximum adhesion force between water droplet and methylated glass increases with decreasing value of the most stable contact angle, a correlation that is similar to that reported for smooth polymers.