Measurement of Temporal Change in Shape of a Suspended Droplet Containing Particles Using Light Scattering

In contrast to a convex droplet, the particles contained in a suspended droplet accumulate near its bottom and can reflect light passing through it. The intensity of the light scattered by the particles near the bottom depends on the radius of curvature of the droplet at the bottom, and therefore this enables the detection of the shape change of the droplet with high sensitivity. We show that during the evaporation of a water droplet containing gold particles, the intensity of the scattered light initially increases gradually, after which it decreases rapidly immediately before the droplet evaporates completely. This change elucidates that the suspended droplet is rapidly flattened after its radius of curvature decreases, and the particles contained in it strongly affect its evaporation process, particularly for small droplets. This phenomenon can be used to more brightly illuminate the surface of a droplet relative to the interior.