Measuring colloidal forces using evanescent wave scattering

The evanescent wave scattering technique total internal reflection microscopy has enabled the direct measurement of the mean potential energy of interaction between a Brownian particle and a flat surface. With a distance resolution of 1 nm and a force resolution of 10 fN, this technique has successfully measured a variety of colloidal forces. Recent measurements of van der Waals interactions have given rise to new theories for the effect of surface roughness on the interaction. In addition, recent measurements of depletion interactions have shown that energetic as well as entropic effects must be considered when computing the interaction potential.