Detachment of colloidal particles from collector surfaces with different electrostatic charge and hydrophobicity by attachment to air bubbles in a parallel plate flow chamber

The detachment of polystyrene particles adhering to collector surfaces with different electrostatic charge and hydrophobicity by attachment to a passing air bubble has been studied in a parallel plate flow chamber. Particle detachment decreased linearly with increasing air bubble velocity and decreasing liquid/vapour interfacial tension, regardless of the collector surface properties. However, particle detachment from hydrophilic, positively charged surfaces [3-(2-aminoethylamino)propyldimethoxysilane-coated glass, water contact angle 33 degrees] was most sensitive to variations in air bubble velocity and liquid/vapour interfacial tension, while detachment from hydrophobic, negatively charged surfaces (dimethyldichlorosilane-coated glass, water contact angle 96 degrees) was affected least. The influence of air bubble velocity was predominantly through the bubble/particle contact time, which needs to be long enough to allow sufficient thinning of the liquid film between the bubble and the particle for the detachment forces to become effective. On the hydrophobic collector surfaces, this thinning is assisted by a nearly spontaneous de-wetting of the collector surface, therewith decreasing the influence of other factors, such as air bubble velocity or liquid/vapour interfacial tension. Upon multiple passages of air bubbles approximately 80% of the particles were eventually detached, regardless of the properties of the collector surfaces, illustrating that the probabilities of detachment by multiple air bubble passages are additive.