STABILITY OF THREE-PHASE FOAM UNDER ULTRASONIC IMPACT

Wave action on a disperse system, in particular foam, is of particular importance for processes accompanied by undesirable foam formation. Foams containing additives of solid particles or Pickering foams are characterized by a significant lifetime in the gravitational field in the absence of any external influences. In this case, foams stabilized by silica hydrophobized with short-chain surfactant hexylamine (at surfactant concentrations of 18-55 mmol/l) have an abnormally high lifetime exceeding two months. The study of the effect of ultrasonic treatment on the stability of such dispersed systems showed the effectiveness of using this method for rapid destruction of three-phase foams. In particular, the destruction of 90% of the foam layer of different composition under the action of ultrasound occurred within a time not exceeding 10 minutes. The degree of destruction of Pickering foams under wave action is determined by the concentrations of solid phase and surfactant, as well as by the chemical nature of these stabilizers. It is shown that the increase in the concentration of solid silica particles in the initial suspension led to a decrease in the susceptibility of the resulting three-phase foams to ultrasound. In this case, the greatest stability is observed not at some maximum content of short-chain stabilizer hexylamine, but at the concentration corresponding to the largest contact angle Ɵ. Thus, three-phase foams stabilized by modified aerosil at the edge angle of wetting of particles Ɵ = 47 0 and concentration of hexylamine 53 mmol/l showed the lowest susceptibility to ultrasound. Further increase of hexylamine concentration up to 73 mmol/l resulted in a decrease of dispersed system lifetime up to 3.5 minutes. The data obtained correlate with the destruction of foams when they were studied in cells with porous filter under the action of applied differential pressures. When replacing the short-chain surface-active modifier with long-chain cetyltrimethylammonium bromide (CTAB), an increase in the resistance of foams to ultrasonic effects was observed even at a lower degree of surface modification. It is shown that the process of gel formation in the dispersion medium of three-phase foam can serve as an additional factor of stability of Pickering systems to wave action.