Interaction Forces between Silica Surfaces in Wet Cyclohexane

Interaction forces between silica surfaces in wet and dry cyclohexane are measured using atomic force microscopy. A strange (strong?) attractive force acts between the surfaces with increasing water concentration, which is much further and stronger than the van der Waals attractive force. The attractive force decreases monotonically as the approaching velocity between two surfaces increases. The following results are obtained concerning the adhesion force: i) the probability for strong adhesion force increases with water concentration, ii) a finite contact time is required for the appearance of strong adhesion force, iii) hydrophobilization of one surface brings a sharp decrease in adhesion force. These results suggest that the strong adhesion force is caused by the formation of water bridge.