Forces and friction between hydrophilic and hydrophobic surfaces: Influence of oleate species

• Published in: Journal of colloid and interface science Vol. 313; no. 2; pp. 735 - 746
• Main Authors: Theander, Katarina, Pugh, Robert J., Rutland, Mark W.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 15.09.2007; Elsevier
• Subjects: Adsorption; AFM; Cellulose; Chemistry; Colloidal probe; Colloidal state and disperse state; Deinking; Exact sciences and technology; Fatty acid; Friction; Fysikalisk kemi; General and physical chemistry; Kemi; Nanotribology; NATURAL SCIENCES; NATURVETENSKAP; Physical chemistry; Sodium oleate; Surface and colloid chemistry; Surface force; Surface physical chemistry; Yt- och kolloidkemi; Nanotribology; Sodium oleate; Surface force; Friction; Adsorption; Fatty acid; Cellulose; AFM; Colloidal probe; Deinking; Atomic force microscopy; Force; Hydrophobicity; Fatty acids; Sodium
• ISSN: 0021-9797; 1095-7103; 1095-7103
• DOI: 10.1016/j.jcis.2007.05.016

The atomic force microscope has been used to investigate normal surface forces and lateral friction forces at different concentrations of sodium oleate, a frequently used fatty acid in the deinking process. The measurements have been performed using the colloidal probe technique with bead materials consisting of cellulose and silica. Cellulose was used together with a printing ink alkyd resin and mica, whereas silica was used with a hydrophobized silica wafer. The cellulose–alkyd resin system showed stronger double layer repulsion and the friction was reduced with increasing surfactant concentration. The adhesive interaction disappeared immediately on addition of sodium oleate. The normal surface forces for cellulose–mica indicated no apparent adsorption of the sodium oleate however, the friction coefficient increased on addition of sodium oleate, which we ascribe to some limited adsorption increasing the effective surface roughness. The silica–hydrophobic silica system showed a completely different surface force behavior at the different concentrations. An attractive hydrophobic interaction was evident since the surfaces jumped into adhesive contact at a longer distance than the van der Waals forces would predict. The strong adhesion was reflected in the friction forces as a nonlinear relationship between load and friction and a large friction response at zero applied load. Indirect evidence of adsorption to the hydrophilic silica surface was also observed in this case, and QCM studies were performed to confirm the adsorption of material to both surfaces. Force and friction measurements have been performed using the atomic force microscopy and the colloidal probe technique in liquid environment at different concentrations of sodium oleate.