Microscale thermal and contact line behavior of evaporating droplets on surfaces with varying wettability

• Water droplet evaporation studied on surfaces with different wettability. • Superhydrophilic surfaces show strong contact line pinning and sharp thermal spikes. • Time lag between MCL motion and thermal response decreases with increasing surface wettability. • Higher wettability accelerates evaporation; superhydrophilic surfaces evaporate fastest. • Hydrophobic surfaces have higher bulk heat flux due to weaker interfacial transfer. The evaporation behavior of droplets varies across superhydrophilic, moderately hydrophilic, and hydrophobic surfaces due to differences in surface wettability, which influence the dynamics of the multiphase contact line (MCL), the shape of the microscopic contact, and subsequently the local heat and mass transfer. Understanding how wettability affects evaporation and heat transfer mechanisms on the microscale is crucial for achieving effective surface engineering, advancing thermal management technologies, and improving the efficiency of heat transfer systems. This study employs micro-electromechanical (MEMS) devices fabricated with varying wettability, integrating a resistance heater, thin-film resistance temperature detectors (RTDs), and an interdigitated electrode (IDE) capacitance sensor array in order to achieve real-time simultaneous measurement of local surface temperature, heat flux, and precise tracking of the MCL during the evaporation of 3 µL water droplets. Experimental results reveal distinct evaporation dynamics controlled by wettability: superhydrophilic surfaces exhibit strong contact line pinning with rapid evaporation times compared to moderately hydrophilic and hydrophobic surfaces, which display stick–slip and receding contact line behavior. The capacitance sensors detect MCL movement between 1 and 2 s before thermal responses, highlighting the dominant role of contact line dynamics in local heat transfer, accounting for over 70 % of temperature variation during evaporation. Analysis of local vertical heat flux demonstrates that both wettability and MCL speed influence thermal transport in the vicinity of the MCL, where the droplet contacts the heating surface. These findings provide new insights into microscale evaporation phenomena, enabling the design of efficient thermal systems by exploiting surface wettability control.