Interactions between hydrophilic and hydrophobic surfaces on microscopic scale and the influence of air bubbles as observed by scanning force microscopy in aqueous and alcoholic mediums

In the present study interactions between hydrophilic and hydrophobic surfa ces were studied on a microscopic scale by using scanning force microscopy (SFM). Gold-coated surfaces were chemically modified to be hydrophobic or h ydrophilic by self-assembly monolayers based on thiols with different end-g roups (COOH, CH3). The adhesion forces between hydrophilic tips and hydroph ilic or hydrophobic surfaces were measured in water/ethanol mixtures by rec ording force-distance curves. The measurements in water/ethanol mixtures sh ort an increase of the adhesion forces due to the increase of the water con tent. The observed interactions are of short range within few nm. In some f orce-distance curves with hydrophobic tips a stepping in the retracting par t was observed which could be attributed to air bubbles in the vicinity of the tip-surface junction.