Molecular Dynamics-Based Approach for Laser-Induced Cavitation Bubbles: Bridging Experimental and Hybrid Analytical-Computational Approaches.

Cavitation phenomena and their importance drive research efforts to characterize their behavior through experimental, analytical, and computational approaches. However, experimental approaches struggle to capture molecular-level details; analytical methods are often limited in application and accuracy; and computational techniques may miss key physical phenomena such as phase transitions. To address these limitations, the current study introduces laser-based molecular dynamics (MD) based on a coarse-grained (CG) model as a promising approach to investigate the dynamics of cavitation bubbles at the molecular-level, covering nucleation, growth, collapse, evaporation, phase transition, liquid-vapor interphase, and subsequent regrowth/collapse cycles. The research was performed with an experimental study on millimeter-scale bubble cavitation under ambient and free conditions. The obtained observations were used to model the laser-liquid interaction. This analytical model was then implemented in an MD method to investigate the dynamics of the nanobubbles. The simulations revealed that directing a 1 fJ laser pulse at water generates a hot plasma, which expands spherically through collision cascades and generates a nanobubble. The nanobubble grows to a maximum radius of 5.26 nm and collapses within 17 ps, followed by subsequent regrowth/collapse cycles. At maximum radius, the vapor-liquid interphase exhibits a thickness of 0.8 nm with a density range of 0.105 to 0.840 g/cm3. Cold evaporation temperatures ranging from 300 to 315 K and vapor density of 4.5-1.5+1.5 × 10-5 g/cm3 were captured inside the nanobubble. These results, which align with experimental data, confirm the effectiveness of the proposed MD-based algorithm in investigating laser-induced cavitation nanobubbles. Moreover, this algorithm can be extended to investigate radical species of water or chemical reactions under laser radiation and cavitation in all-atom model simulations.