Dynamic interfacial tension in water/n-pentane system: An experimental study using the oscillating-jet method

• Reports the water–hydrocarbon dynamic interfacial tension for the first time.
• Interfacial-tension measurements were made using the oscillating-jet method.
• Water was jetted into a mixture of saturated common vapors of n-pentane and water.
• The interfacial tension decreased to its equilibrium value during the first ~50 ms.
• The relaxation of the tension was formulated based on an adsorption kinetics model.

The interfacial tension working at an interface created by sudden contact of liquid water with saturated common vapors of n-pentane and water under atmospheric pressure (0.101 MPa) was experimentally studied, focusing on the behavior of its relaxation to an equilibrium value in response to the progress of the adsorption of n-pentane molecules onto the interface. The oscillating-jet method was used to measure the dynamic interfacial tension, i.e., the interfacial tension varying with time during a short relaxation period (less than 0.1 s) after the creation of the interface. It was observed that during the first ~50 ms after the creation of the interface, the tension quasi-exponentially decreased from the normal surface-tension value for pure water (70.5 mN/m) to the equilibrium value (61.5 mNm) which had been obtained in a previous study using the pendant-drop method. An attempt was made to correlate the obtained “interfacial tension versus time” data based on an adsorption/desorption kinetics model.