Surface tension measurements of the aqueous phase using a Sigma 70 tensiometer (KSV Instruments Ltd., Finland) at 25 °C. The Wilhelmy plate technique was applied in the Wilhelmy Constant Run programme mode. A platinum plate was partially immersed into the surface layer of an aqueous phase and the monitored surface tension decreased with time while the plate remained into position. The analysis ceased when the surface tension value was stabilized. Prior to each analysis, the surface tension of deionised water was measured as control.