The relative importance of contact-angle hysteresis and work of adhesion on droplet “roll-off” or sliding angles

A series of mixed monolayers formed by self-assembly of alkanethiols on gold exhibits complementary wetting behavior for hexadecane and water that allowed us to independently assess how strongly the contact-angle hysteresis and work of adhesion of contacting liquid droplets influence their sliding angles on these surfaces. Near-constant values of advancing contact angle, and thus work of adhesion, for droplets of water across this series enabled the study of the relationship between the contact-angle hysteresis and the sliding angle. The same surfaces exhibited near-constant hysteresis, but varying values of work of adhesion, with hexadecane as the wetting liquid. These complementary studies confirmed a correlation between droplet sliding angle and hysteresis, with the work of adhesion playing little or no role.