Measurement of ultralow interfacial tension with a laser interface manipulation technique

Abstract

The liquid surface or interface is deformed slightly by a laser beam passing through it. Based on this principle, a method to measure the liquid-liquid interfacial tension is developed. The interfacial tension is determined from the deformation, of which the displacement is measured with another probe laser in a noncontact manner. The measurements were available in two different senses: the constant displacement under continuous laser irradiation gives the static value, and the frequency response spectrum of the displacement under modulated excitation gives the dynamic value. To demonstrate the usefulness of this method, a series of experiments were conducted in the interface between heptane and water containing aerosol OT as a surfactant. The interfacial tension was controlled by the concentration of added NaCl, and measurements were made over the range from 1 microN/m to 100 mN/m of the tension. The results were in good agreement with the previous works. This method would be a new tool for the studies of various interfacial phenomena.

Laser-Induced Hydrodynamic Instability of Fluid Interfaces

“…1), and the height hr of the induced deformation is determined by a balance with the buoyancy and Laplace restoring forces. Then at steady state hr is described by [14]:…”

Dynamic interfacial tension effects in the rupture of liquid necks

“…The resulting pictures were analysed using an in-house program to extract the minimum neck radius versus time for the different systems studied. High surface tensions were measured using the drop weight technique; low interfacial tensions were measured using a spinning drop tensiometer or the surface deformation due to the radiation pressure of a laser beam focused at the surface (Mitani & Sakai 2002). Figure 1 shows pictures of detaching drops for our different systems.…”

Laser microfluidics: fluid actuation by light

“…For instance, a Japanese team exploited the bending of an interface by a laser wave to measure interfacial tensions [46] in a non-contact manner. In a second work [47], they focused their attention on the difficult case of ultra low interfacial tension, for which most of classical techniques fail. Finally, they showed the pertinence of radiation pressure to measure shear viscosities [48].…”