Dewetting kinetics on silica substrates: Three phase contact expansion measurements for aqueous dodecylammonium chloride films

The dewetting kinetics between a small air–liquid interface and a silica (negatively charged in water) planar surface in solutions of dodecylammonium chloride (cationic surfactant) has been investigated using the Scheludko cell and digital high-speed video microscopy. The gas–liquid interface was created at the bottom of a small silica capillary of the cell and then was moved towards the silica planar surface. After the rupture of the liquid films between the interfaces, the expansion of the gas–liquid–solid three-phase contact (TPC) line was observed and recorded using a digital high-speed video microscope system, operating at 1000 frames/s. The surface tension of the surfactant solution was measured using the pendant drop technique. The equilibrium contact angle was measured using the Scheludko–Minings method with a silica micro-sphere. The TPC radius was determined as a function of time and compared against the available hydrodynamic and molecular-kinetic models. The experimental data are described very well by the molecular-kinetic model for the TPC line motion. The hydrodynamic model is in agreement with the experimental data only for a short time after inception of the three-phase contact expansion. A simplified model was developed for predicting the time of the TPC line expansion in flotation.