Measuring capillary wave fluctuations and droplet coalescence in colloidal fluids with light sheet microscopy

We measure capillary wave fluctuations, droplet coalescence, and dripping in a colloidal fluid system by using a custom-built single objective light sheet microscope (SOLS). We acquire volumetric imaging data at several volumes per second with submicron resolution. We show that we can use SOLS to detect capillary fluctuations at the interface of coexisting colloidal fluids. We measure submicron fluctuations and capillary velocities on the order of 0.1 micron per second. We additionally measure the width of the growing bridge that connects a coalescing droplet to the continuous phase. Our SOLS system allows us to acquire fast optically sectioned images for volumetric data collection without needing to move the objective lens. Rather, the focal plane and sheet of excitation light are swept across the sample using a scanning mirror. This method provides fast 3D imaging with minimal mechanical perturbation to the sample.