Determination of contact angle hysteresis of water microdroplets evaporating on hydrolyzed PET foils

Moderately hydrophobic surfaces of PET foils were gradually hydrophilized by their immersion in NaOH solutions of increasing concentration. Then, the contact angle and geometric factors of microliter water drops, deposited on these polymer surfaces, were automatically monitored as a function of evaporation time. Three stages have been identified from the evaporation course of water droplets, allowing us to determine the advancing and receding contact angle and thus their difference (hysteresis).