STUDIES OF THE CONTACT INTERACTION BETWEEN AN AIR BUBBLE AND A MICA SURFACE SUBMERGED IN DODECYLAMMONIUM CHLORIDE SOLUTION

A microscope-based observation method developed by Scheludko and Tchaliovska has been employed to study the wetting properties of hydrophobed as well as initially clean, freshly cleaved muscovite mica submerged in dodecyl ammonium chloride (DAC) solution. The observations made and the results obtained on thin-film lifetimes, contact angle hysteresis, and rates of expansion of the meniscus perimeter reflect the importance of hydrophobic attraction forces as well as of attractive and repulsive electrostatic forces. For clean mica in the very dilute regime, extensive hydrophobation occurs only from the three-phase contact line where a condensed surfactant monolayer apparently forms as a result of electrostatic and hydrophobic attraction. For hydrophobed mica, there is a transition from water-like wetting behavior with marked contact angle hysteresis to hysteresis-free wetting, taking place at about cdac = 1 μMol/L. At higher surfactant concentrations, cdac = 1μmol/L, the wetting properties of initially clean mica and hydrophobed mica, respectively, are quite similar. These latter results are in agreement with parallel surface force measurements. It is inferred that a high flotation recovery of mica can only be achieved when the mica surface is well-covered by a dense, hydrophobic surfactant monolayer. This provides a rationale for “bubble conditioning”. © 1990, American Chemical Society. All rights reserved.