Measurement of long-range hydrophobic attraction forces during bubble/particle attachment (Octadecyltrichlorosilane)

The observation of a “hydrophobic” attractive force between surfaces in an aqueous medium has been made by several investigators, but a good understanding of this phenomenon is not available. A hydrophobic force was first measured between two treated mica surfaces, and has since been observed in other surface geometries and systems. Flotation is a fundamental unit operation used for the separation and removal of contaminants during recycling of paper. Although the technique has proven successful for the separation of components based on their hydrophobic/hydrophilic nature, many fundamental questions remain, including the underlying mechanism(s) responsible for particle attachment to an air bubble. Hydrophobic attraction has been observed in situations that are physically similar to flotation-like settings, and we believe that hydrophobic attraction may be the non-hydrodynamic driving force for attachment of contaminants to air bubbles during flotation.; A report of hydrophobic force measurements between a bubble and particle during attachment, simulating capture and removal of contaminants in flotation deinking, is the subject of this thesis. A force/displacement apparatus has been constructed to simultaneously measure the movements of a particle and bubble surface as the pair are brought close to each other and allowed to attach. Results from the force device show simultaneous measurements of a hydrophobized silica bead and bubble surface during attachment. Interpretation of the two traces, particle displacement and bubble surface deformation, are presented. Long-range attractive forces, with a length-scale up to 2500 nm, were measured between a hydrophobized silica bead and a deformable bubble in pure water. The initial point of contact, a crucial parameter in calculating the separation distance, was determined using high-speed videography. The critical separation distance is an important parameter and may be directly related to the efficiency of bubble/particle attachment in flotation. The critical separation distance is defined as the thickness of the water film between the bead and bubble at the onset of the spontaneous jump to contact. Reproducibility trials show a consistent critical separation distance measured for a given system, but varying from one bead to another.