Coffee-ring deposits of polydisperse particles

Abstract

The coffee-ring phenomenon has attracted attention for spontaneously concentrating suspended inclusions at the tri-phase contact line. Yet, little is known about how the size distribution of particle mixtures affects the annular structure. Here, instead of the classic power-law relation between the ring width and the initial volume fraction for monodisperse spherical particles in evaporative droplets, a logarithmic function is observed for polydisperse particle mixtures mimicking the size distribution of matters in material and biological research (e.g., Gamma distribution). The effect of particle size distribution on the evolution of ring deposits would inspire strategies for diagnostics, assembly, and manufacturing processes.