Jana K. Angarska

Effect of the driving pressure on the rate of thinning of microscopic foam films

Abstract The effect of the driving pressure on the rate of thinning of microscopic foam films from aqueous solutions of nonionic [C 12 (EO) 8 ] and anionic [DDBS] surfactants was studied experimentally. At the ionic strengths of the solutions used (0.024 or 0.1 mol l −1 ) the driving pressure was mainly governed by the capillary pressure, while the disjoining pressure was negligible, especially at a large film thickness. The studied films were obtained in glass cells of different radii ( R c ) of the holder in which the film was formed. The values of the drainage constants ratios ( α 2 / α 1 ), experimentally obtained for films under different experimental conditions were compared to the theoretically calculated ratios of the thinning rates ( V 2 / V 1 ). The deviations from the classical Reynolds law, obtained experimentally, correspond to the dependence of the rate of thinning on driving pressure required by the theoretical approach of Manev–Tsekov–Radoev. The results confirm the conclusions of the approach, accounting for the effect of the film thickness non-homogeneity on the rate of thinning.

Effect of tetrapentyl ammonium bromide adsorption on the electrostatic interactions in aqueous octaethyleneglycol decylether foam films

Foam films from aqueous solutions of octaethyleneglycol–decylether, C10(EO)8 are investigated in the presence of organic electrolyte (tetrapentyl-ammonium bromide (TPeABr) or inorganic electrolyte (KBr). The dependence of the diffuse electric layer potential on the surfactant and electrolyte bulk concentration is quantitafied from the data on the equilibrium films thickness obtained through interferometric measurements. The effect of the organic electrolyte on the film properties is compared to that of the inorganic. It is established that TPeABr affects the electrostatic interactions in the film in a complex manner: as an electrolyte as well as an ionic surfactant. Although being less surface active its adsorption on the film surfaces modifies their charge and adsorption layer composition. It is found that at higher TPeABr concentration (up to 1×10−3 mol l−1) the adsorption of the positively charged TPeA+ ions even results in recharging the surface and unstable (rupturing) films. The TPeABr effect is stronger at lower C10(EO)8 concentration (1×10−5 mol l−1), where the adsorption of the two components is compatible and leads to substantially lower values equilibrium film thickness (heq) and surface potential (ϕ0). The greater participation of TPeABr in the mixed adsorption layers at lower C10(EO)8 concentration is confirmed by data of their composition, which we have obtained by using the Molecular Interaction Parameter (βs=−3.24) between TPeABr and C10(EO)8 at the interface. The MIP can be derived from the surface tension isotherms of the separate components and their mixture.

Critical thickness of foam films stabilized by nonionic, ionic surfactants and their mixtures

Abstract The critical thickness (hcr) for foam films of n-dodecyl β-D maltoside (C12G2) and of its mixed solutions with dodecanol (C12Е0), hexaethyleneglycol dodecyl ether (C12E6) and dodecyl trimethylammonium bromide (C12TAB) of different molar ratio (50:1; 1:1;1:50) at low and high ionic strength was measured interferometrically. It was found that the hcr increases with the increase of the film radius independently of solutions composition. At low ionic strength the type of surfactant affects the critical thickness and the equilibrium state of the film. hcr for the films of mixture with C12E0 increases with the increase of the total surfactant concentration, while hcr for the films of mixture with C12TAB decreases. For the values of the critical thicknesses for films from individual surfactant solutions the following sequence hcr (C12TAB) > hcr (C12E6) > hcr (C12G2) is found. At high ionic strength the quantity of nonionic additive does not substantially affect the value of hcr, while the quantity of ionic additive influences it by two different ways (i) in 50:1 mixture C12TAB supports C12G2 in the reducing of negative charge; (ii) in 1:1 mixture C12TAB recharges the film surfaces.