A Study of Hydrophobic Interactions between Stainless Steel and Silanated Glass Surface Using Atomic Force Microscopy

Abstract

The passive film at a stainless steel surface which consists mainly of chromium and iron oxides, has a surface energy that can be strongly reduced by the adsorption of organic contamination. We have investigated the effect of surface pretreatments of stainless steel on the long-range surface forces and the adhesion forces. Electron spectroscopy for chemical analysis (ESCA) has been used to analyze the chemical composition of the surface film and to estimate the thickness of the organic contamination layer. An atomic force microscope has been used to measure the long-range hydrophobic attraction forces and the adhesion force between the stainless steel surface and a silanated silica sphere immersed in water. The adhesion forces on both the contaminated hydrophobic and cleaned hydrophilic surfaces have been correlated with the interfacial energies obtained by contact angle measurements. Both long-range attractive and adhesive forces are stronger for the noncleaned surface possibly due to the "hydrophobic effect." This hydrophobic interaction becomes neutralized in the presence of hydrophilic groups (i.e., potassium salt) on the surface. On the other hand, contact angle measurements indicate a higher surface energy for the Ar-plasma-treated surface than for the contaminated sample. This shows that these forces are not only dependent on the surface properties but are also markedly dependent on the nature of the surrounding medium, which can drastically alter the interactions between two macroscopic bodies.