Glass Grains Large and Small

Colloids and nano-particles diffuse and thus display self-assembly and phase transitions, just as atoms and molecules. Brownian motion and diffusion were separately studied in the 19th century by a variety of gentlemen including botanists, priests and even chemists. A debate spanning almost 75 year eventually brought the insight that visible Brownian motion and diffusion of invisible species are identical manifestations of thermal energy. Via the work of Einstein and Perrin on diffusion of single colloids, this insight yielded strong support for the existence of molecules- and a way to count them via Avogadro’s number. Nowadays colloid- and nano-science focus on self-assembly of interacting particles; a challenging field that seemingly reduces free-particle diffusion to a simple reference case. Perhaps not that simple given that a wrong interpretation of diffusion of single colloids was once rewarded with a Nobel price…