Microscopic particles found in engineering, materials science and soft matter physics are often confined: this restricts their motion and may therefore change their behavior. Spherical particles under confinement have been studied extensively, but less is known for particles that aren’t perfect spheres. In this work, together with Stefania Ketzetzi and coworkers, I’ve looked at how micron-sized colloidal dumbbell particles dance on top of a glass substrate.
We’ve constructed a very cheap but powerful holographic microscope using a single-wavelength LED mounted on an existing microscope. In this way, we can fit a scattering model to the images and extract the precise 3D location of the particles. By using reference particles that are fixed on the glass substrate, we also determine the position and tilt of the substrate very accurately.
From our experiments, we find that the interplay of gravitational and electrostatic forces causes the smaller dumbbells to show large out-of-plane rotations, while the larger dumbbell shows only small fluctuations. Surprisingly, the smaller dumbbell particles never lie completely flat with respect to the substrate! Our results highlight the complex behavior of non-spherical particles close to walls and we hope that this will aid in developing quantitative frameworks for arbitrarily-shaped particle dynamics in confinement. For the full story, you can find the article here: