Generation and Observation of Long-Lasting and Self-Sustaining Marangoni Flow

Speleothem-Inspired Copper/Nickel Interfaces for Enhanced Liquid-Vapor Transport by Marangoni and Soret Effects

Geological formations have superior wickability and support the absorption of water and oils into narrow spaces of Earth's crust without external assistance. In this study, we present speleothem inspired heterogeneous porous and wicked copper (Cu)/nickel (Ni) interfaces for enhanced nucleate boiling of water/ethanol mixtures for energy-efficient separation processes. The incorporation of Ni strands within the copper particle matrix significantly enhanced heat transfer. Compared to plain copper, the Cu/Ni speleothem surfaces exhibited a 61% increase in the heat transfer coefficient for water/ethanol mixtures and a 332% increase for water, with a 58% faster onset of nucleate boiling. This enhancement was attributed to Marangoni and Soret effects at the Cu/Ni interfaces, driven by surface tension and concentration gradients. Furthermore, the synergistic wicking action of the Ni strands facilitated rewetting of the surface, replenishing liquid to the porous nucleation sites and preventing surface dry-out, thereby improving the overall heat transfer performance.

Affinity of Amphiphilic Molecules to Air/Water Surface

The affinity of amphiphiles to the water/air surface was modeled by adapting Eberhart's equation. The proposed method successfully describes surface tension for all amphiphilic structures, including alkanols, carboxylic acids, nonionic, ionic, and Gemini surfactants. The model is more effective than conventional analysis for amphiphiles with multiple ionic states. The prediction was consistently validated at different temperatures and nonaqueous solvents. The modeling results show a linear correlation between surface affinity and hydrophobicity/hydrophilicity. For alkanols, the affinity increment is 2.84 kJ/mol per CH2 group, the same as the reported hydrophobic energy from monomer to aggregate for nonionic surfactants. For carboxylic acids, the affinity increment per CH2 group is 3.18 kJ/mol, incorporating the degree of acid dissociation. The affinity-hydrophilicity correlation is approximately -0.22 kJ/mol per oxyethylene group. The affinity constant can be obtained for all classes of amphiphiles to clarify the relationship between the molecular structure and surface activity.