Drying of sessile droplets of laponite-based aqueous nanofluids

Formation of the ring-like pattern by nano-particles of the desiccated droplet of a laponite-based aqueous nanofluid (the well known ‘coffee-ring effect’) is studied. The temperature was controlled and fixed (T = 300 K). The laponite concentration was controlled and varied in order to investigate its effect on the pattern formation. It was observed that the coffee-ring effect vanishes if concentration of laponite exceeds 5%. A simple model for analysis of colloidal sessile droplet desiccation is proposed. The model describes correctly dynamics of the drying droplet profile and the final shape of the dried film (deposit). The model is based on the mass conservation law and reasonable assumption that deposit (gel phase) prevents the flows.