Simultaneous measurement of surface tension and kinematic viscosity using thermal fluctuations

We have developed a surface laser-light scattering apparatus to measure simultaneously surface tension and kinematic viscosity. In this method, we can obtain the surface properties by the laser heterodyne detection of light scattered from thermally excited capillary waves (called "ripplon"), which are typically of low amplitude (∼1 nm) and a characteristic wavelength (∼100 μm). Two gratings (d=100 and 200 μm) were employed to select the wave number of the capillary waves and to produce a reference beam for heterodyne detection. It was found through an experimental study on water that this contact-free method has considerable potential for application to measurements under extreme conditions such as high temperatures and high pressures.