Chemical wetting hysteresis

Experiments performed on model systems show that the contact angle of a liquid on a solid depends strongly on very small-sized chemical heterogeneities of the solid surface. The measurement of the maximum advancing and minimum receding contact angles of liquid Sn on Si-SiO2 surfaces was performed by stretching and compressing a liquid bridge between two parallel plates. The shape and distribution of the micro-defects are controlled by fabricating model chemically-heterogeneous surfaces. The wetting hysteresis is found to depend on the linear density of the chemical defects as the chemical pinning of the triple line occurs in only one (advancing or receding) spreading direction. Moreover, the inversion of the chemistry of the substrate and the defect leads to different width of the hysteresis. These results agree fairly well with the recent theoretical descriptions of wetting phenomena.