Nanoscale resolution of thin film profile of the evaporating water droplet induced by substrate heating

The water film morphology near the triple phase contact line during the evaporation is investigated experimentally due to importance of the thin film region in partial wetting evaporation regime. The state-of-the-art tapping-mode atomic force microscopy (TM-AFM) is used to get the high resolution film profile goes down to 2 nm from the contact line. The substrate was heated by PI film heater. The receding speed was less than 25 nm/s. The dominant results indicate that the film profile goes down straightly to the surface till 2 nm from the substrate. However, small bending has been observed below 20 nm, occasionally. So, it can be claimed that for low evaporation rate the microscopic contact angle equals to the optically detectable macroscopic contact angle. This result can be used to simplify the heat transfer modeling in partial wetting evaporation.