A STUDY OF HYDROPHOBIC INTERACTIONS BETWEEN STAINLESS-STEEL AND SILANATED GLASS-SURFACE USING ATOMIC-FORCE MICROSCOPY

The passive him at a stainless steel surface which consists mainly of chromium and iron oxides, has a surface energy that can be strongly re duced by the adsorption of organic contamination, We have investigated the effect of surface pretreatments of stainless steel on the long-ra nge surface forces and the adhesion forces, Electron spectroscopy for chemical analysis (ESCA) has been used to analyze the chemical composi tion of the surface him and to estimate the thickness of the organic c ontamination layer, An atomic force microscope has been used to measur e the long-range hydrophobic attraction forces and the adhesion force between the stainless steel surface and a silanated silica sphere imme rsed in water. The adhesion forces on both the contaminated hydrophobi c and cleaned hydrophilic surfaces have been correlated with the inter facial energies obtained by contact angle measurements, Both long-rang e attractive and adhesive forces are stronger for the noncleaned surfa ce possibly due to the ''hydrophobic effect.'' This hydrophobic intera ction becomes neutralized in the presence of hydrophilic groups (i.e., potassium salt) on the surface, On the other hand, contact angle meas urements indicate a higher surface energy for the Ar-plasma-treated su rface than for the contaminated sample. This shows that these forces a re not only dependent on the surface properties but are also markedly dependent on the nature of the surrounding medium, which can drastical ly alter the interactions between two macroscopic bodies. (C) 1995 Aca demic Press, Inc.