Temperature-dependent water slip flow combined with capillary evaporation in graphene nanochannels

The discovery of ultrafast water flow in graphene channels holds significant implications for various applications like electronics cooling, thermally driven energy harvesting, and solar-driven desalination. However, existing slip flow measurements on graphene are confined to room temperature, limiting our understanding of temperature-dependent behaviors and constraining potential thermal applications. Here, we simultaneously measured water slip lengths and evaporation fluxes in graphene nanochannels with depths ranging from 78 to 290 nm, spanning a temperature range from room temperature up to 85 °C. This was achieved by employing a capillary flow model combined with evaporation, a factor that cannot be disregarded at elevated temperatures. The measured water slip lengths ranged from 20 nm to 80 nm, exhibiting a decrease with increasing temperature and an increase with greater channel depths. The temperature-dependent slip length can be attributed to enhanced momentum transfer at the solid-liquid interface at elevated temperatures, while the observed channel depth dependence may result from stronger electrical-double-layer interactions with decreased channel depths. Additionally, the capillary evaporation fluxes increased with rising temperatures and greater channel depths, effectively explained by the capillary evaporation theory.