High precision characterization of a binary fluid interface using surface light scattering spectroscopy

Thermally excited capillary waves (ripplons) with an rms height of ~1 nm perturb any fluid interface. The Doppler spectrum of these ripplons, which can be characterized by Surface Light Scattering Spectroscopy (SLSS), depend upon interfacial properties such as surface tension and surface viscoelasticity, via the capillary wave surface response function, a refinement of the classical dispersion equation. Innovative optical design has increased signal and signal-to-noise ratio. This enhances measurement accuracy over the entire range of wave numbers, while enabling measurements at higher wave numbers above 1500/cm. We demonstrate the validity of the technique with high precision and high accuracy measurements of standard fluids. Subsequent measurements of pentane/2-methyl pentane mixtures anticipate an upcoming NASA microgravity experiment intended to optimize the effectiveness of wickless heat pipes for space flight applications.