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

• Published in: Europhysics letters 2000-12, Vol.52 (5), p.551-556
• Main Authors: Papastavrou, G, Akari, S, Möhwald, H
• Format: Article
• Language: English
• Subjects: 61.16.Ch; Chemistry; Exact sciences and technology; General and physical chemistry; Solid-liquid interface; Surface physical chemistry
• ISSN: 0295-5075; 1286-4854
• DOI: 10.1209/epl/i2000-00472-2

In the present study interactions between hydrophilic and hydrophobic surfaces were studied on a microscopic scale by using scanning force microscopy (SFM). Gold-coated surfaces were chemically modified to be hydrophobic or hydrophilic by self-assembly monolayers based on thiols with different end-groups $(\ab{COOH,CH}_3)$. The adhesion forces between hydrophilic tips and hydrophilic or hydrophobic surfaces were measured in water/ethanol mixtures by recording force-distance curves. The measurements in water/ethanol mixtures show an increase of the adhesion forces due to the increase of the water content. The observed inter actions are of short range within few nm. In some force-distance curves with hydrophobic tips a stepping in the retracting part was observed which could be attributed to air bubbles in the vicinity of the tip-surface junction.