Surface Forces Measured Between Xanthate-Coated Gold Surfaces

Abstract

Direct force measurements were conducted between macroscopic gold surfaces using an atomic force microscope (AFM). The gold surfaces were hydrophobized in potassium amyl xanthate (KAX) and potassium ethyl xanthate (KEX) solutions at open circuit potentials. The force vs. distance curves obtained in the xanthate solutions showed the presence of long-range hydrophobic forces, without evidence for nanobubbles causing the attraction. In general, the hydrophobic force increased with xanthate concentration, immersion time, and contact angle. It was found also that hydrophobic force becomes considerably weaker after longer immersion times, which can be attributed to multi-layer formation. Further, the hydrophobic force became substantially stronger when a xanthate solution was replaced by deionized water, indicating that hydrophobic force becomes the strongest in pure water. The results obtained in the present work may be useful for improving flotation practice and shed lights to better understanding the origin of the hydrophobic force.