Advancing and receding angles – Dynamic contact angle measurements on mixed alkyl monolayers

Mixtures of 1-decene and methyl-10-undecenoate with different mole fractions were used to prepared mixed monolayers on silicon (1 0 0) surfaces. The formed layers were characterized by dynamic contact angle measurements of two different liquids using the dynamic sessile drop method. The advancing and receding contact angles as well the calculated molar wetting free energies decreased with increasing mole fraction of methyl-10-undecenoate. Otherwise the molar dewetting free energies as well as the contact angle hysteresis stay nearly constant. A difference in the wetting and dewetting properties on mixed monolayers is observed, whereby mainly dispersive interactions are responsible for wetting. Furthermore we show that the contact angle hysteresis is independent of surface roughness, surface composition and surface free energy, which indicates that neither surface roughness nor heterogeneities are responsible for this hysteresis. We attribute the hysteresis to interactions between the liquid and the silicon substrate.