*2.2. Methods*

#### 2.2.1. Equilibrium Surface Tension

Surface pressure measurements were performed using the sensor of a KSV LB-5000 Langmuir balance system (KSV-NIMA, Biolin Scientific, Spoo, Finland). The surface pressure is defined as Π = γ<sup>0</sup> − γ, being γ<sup>0</sup> and γ the surface tension of pure solvent, and solution, respectively. Disposable 20.6 mm paper (KSV-NIMA) or Pt-Wilhelmy probes were used. The measuring cell (10 cm3) is made of Teflon and the temperature was controlled by circulating water from a thermostat (Lauda ALPHA RA 8, Lauda-Königshofen, Germany) through a jacket placed at the bottom of the cell. The temperature near the surface is measured with a 0.01 ◦C precision using a calibrated Pt-100 sensor. All measurements were performed at 22 ◦C. For the measurements, the Teflon recipient is filled with an accurately measured amount of Mili-Q water, a small accurately measured amount of stock concentrated surfactant solution is then added to the water in order to prepare, in situ, the surfactant solution at the desired concentration. The solution is left for 60 min to stabilize before surface pressure measurements are carried out.
