Interfacial dynamics of water droplets on graphite: Wetting, evaporation, and diffusion behaviors up to 150 °C and...

Interfacial dynamics of water droplets on graphite determine the performances of material synthesis, deep geo-energy recovery and storage, etc., where high temperature and high pressure prevail. However, these dynamics under such harsh conditions are rarely explored. Therefore, we quantified wetting and evaporation characteristics as a function of temperature (25-150 °C), pressure (5 and 10 MPa), and gas type (CO₂ vs N₂) using droplet profile measurements and estimated diffusion coefficients (D) via theoretical analysis. Results showed that a higher temperature led to a smaller contact angle (θ) and a larger evaporation rate. Specifically, for CO₂ at 10 MPa, as temperature increased from 25 to 100 °C, θ decreased dramatically from 156° to 86°, indicating a transition from strong gas-wet to intermediate-wet; evaporation was negligible. As temperature further increased from 100 to 150 °C, θ decreased slowly from 86° to 69°, indicating a shift from intermediate-wet to weakly water-wet; the evaporation rate increased by nearly 12 times (from 0.006 to 0.072 μL·s^-1). In contrast, for N₂ at 10 MPa, θ decreased linearly from 91° to 73° as temperature increased from 25 to 150 °C. A higher pressure resulted a larger θ for both CO₂ and N₂. Finally, the estimated D under the evaporation conditions (100-150 °C at 5 and 10 MPa) ranged from 1.58×10^-6 to 6.18×10^-6 m²·s^-1, showing a weak dependence on thermo-physical parameters and gas type. These results provide significant insights into interfacial dynamics of water droplet on carbonaceous surfaces under harsh conditions.