Dynamic measurement of the spreading droplet's profile on a submicron scale using the transmission interference fringe technique

Recently, the interference fringe technique has been introduced to measure the nanoscale thickness of droplets. The proposed configuration involved using a large incidence angle on the flat substrate. However, the light collection efficiency is significantly low with a large incidence angle on the flat substrate, making its configuration infeasible for real measurement. Hence, we propose a prism configuration that significantly increases collection efficiency by more than sevenfold. With this configuration and an extended working distance, we show that the transmission interference (TIF) technique can monitor the droplet’s thickness variation during the liquid (Silicone oil) spreading on a submicron scale. Various viscosities of Silicone oil (SO) are used to study the characteristics of droplet spreading on a flat glass surface. With a submicron-scale droplet’s thickness, the precursor film will be investigated for the adiabatic and diffuse film regions over time. This observation is unique because submicron-scale thickness measurement is not easily achieved without a sophisticated setup, such as a microscope, an ellipsometer, or an atomic force microscope, under ambient conditions. Furthermore, the TIF can show real-time diagnostics of the liquid droplet spread over a large area.