Adhesion between hydrocarbon particles and silica surfaces with different degrees of hydration as determined by the AFM colloidal probe technique

Adhesion between oily contaminants and soil particles is a key factor controlling oil release during soil decontamination using wet separation processes. Previous research reports showed that hydration of the soil components, mainly silica particles, governs the oil release efficiency. In this work, the adhesion force between polyethylene particles and silica surfaces with different degrees of hydration obtained by thermal treatment and silanation was measured in an aqueous environment using the atomic force microscopy colloidal probe technique. The adhesion force increases significantly with dehydration of the silica surface and the subsequent increase in hydrophobicity. It was found that experimental adhesion forces measured in the polyethylene-water-silica system are in good agreement with the values calculated theoretically using the Lifshitz/van derWaals-Lewis acid/base interaction theory for highly hydrophobic silica substrates. This agreement is less satisfactory for hydrophilic and slightly hydrophobized silica. It is hypothesized that a thin film of water is strongly adsorbed to the silanol groups on the silica surface and protects the silica surface against its "dry contact" with the polyethylene particle during the atomic force microscopy surface force measurements.