Interfacial and surface tensions of toluene/water and air/water systems with nonionic surfactants Tween 20 and Tween 80
2016
Bąk, Agata | Podgorska, Wioletta
Interfacial and surface tensions were measured at 25°C for the toluene/water and air/water systems with dissolved nonionic surfactants Tween 20 or Tween 80. Dynamic surface/interfacial tensions were measured with the use of the drop volume method and were successfully fitted with the Hua and Rosen equation with characteristic times t*. Static surface/interfacial tensions were determined from extrapolation of the dynamic data to t→∞ on σ or γ versus t⁻¹/² graphs. Obtained results were verified by measurements performed with the use of the Wilhelmy plate method. Critical micelle concentrations for considered surfactants were determined as well as maximum surface excess, minimum surface area per adsorbed molecule and diffusion coefficients were calculated for both fluid/fluid systems. The Frumkin adsorption isotherm was assumed and the Frumkin equation of state fits the experimental static surface/interfacial tensions well. Although the difference between HLB numbers of studied Tweens is small, it is sufficient to observe a different surface activity of surfactants at the air/water surface and toluene/water interface. Performed measurements and analysis give a deeper insight into the surface effects exerted by the nonionic surfactants such as Tween 20 and Tween 80, which in an agitated liquid/liquid dispersions are a source of the additional disruptive stresses generation.
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