Role of DTAB and SDS in Bubble-Particle Attachment: AFM Force Measurement, Attachment Behaviour Visualization, and Contact Angle Study

Atomic force microscopy (AFM) and contact angle measurements were used to study the role of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulphate (SDS) in bubble-particle attachment. The results show that the forces between bubbles and the hydrophilic glass particle were always repulsive in the absence of DTAB and SDS. An attractive hydrophobic force was induced when the particles became hydrophobic, and the force was proportional to the water contact-angle. In the presence of DTAB and SDS, the cationic head group of DTAB adsorbed onto the negative hydrophilic glass surface as a monolayer and thus induced a hydrophobic force. However, at a high DTAB concentration, the DTAB molecules began to adsorb as a bilayer, reverting back to a hydrophilic surface. The hydrophobic force disappeared and the water film between the bubble and particle was stabilised under the repulsive double-layer force. The anionic SDS molecules could not adsorb onto the hydrophilic glass surface. The repulsive force always dominated the bubble-particle interaction. In the case of hydrophobic glass, the hydrophobic force decreased, and even disappeared, with the addition of DTAB and SDS. All the findings from the AFM force curves were consistent with the attachment behaviour and contact angle results.