Acoustothermal Promotion of Bubble Nucleation on Nanostructured Cu Surfaces: A Molecular Dynamics Study

The high-intensity vibration is a highly promising method for accelerating bubble nucleation, given the significant acoustic-thermal effects at the nanoscale. The enhancement effect of vibration on the boiling process on a rough substrate was explored using the molecular dynamics method. The results show that under high-frequency vibration conditions, water molecules are simultaneously subjected to both thermal fluctuations and pressure waves. Specifically, the substrate vibration induced periodic fluctuations of pressure in the neighboring region, which was conducive to the emergence of cavities. When the vibration frequency is raised from 100 to 200 MHz, or the amplitude is increased from 3 to 4 Å, the phase transition initiation time is shortened from 0.38 to 0.12 or 0.14 ns, thus effectively promoting the phase transition process. In addition, the increase in nanopillar height or the enhancement of hydrophobicity leads to the expansion of the high-potential energy region near the substrate, which creates favorable conditions for the phase transition process. However, both the enhancement of hydrophilicity and the increase in nanopillar height were unfavorable to the retention of bubbles. Further analysis revealed that the water molecules in the vibrational state were able to maintain higher kinetic and potential energy levels with the extension of the preliminary heating time, which accelerated the phase transition process. However, when the number of hydrogen bonds near the substrate reached a steady state, the continued extension of the heating time was no longer effective at promoting the phase transition.