Alternating electric fields induce the collapse and structural transformation of nanobubbles

Nanobubbles in microfluidic systems exhibit high stability and unique interfacial properties, but precise control of their morphology, interfacial structure, and position remains challenging. External electric fields, particularly in the terahertz range, can interact with vibrational and rotational modes of interfacial water molecules, potentially providing a non-contact approach to modulate hydrogen-bond networks and molecular orientation at the gas-liquid interface, enabling dynamic regulation of nanobubble behavior in confined microfluidic environments.

Molecular dynamics simulations, coupled with self-developed analysis codes, were conducted to explore the morphology evolution, hydrogen-bond network, and interfacial molecular orientation of nanobubble exposed to terahertz alternating electric fields.

The results demonstrate that terahertz electric fields exert a significant regulatory effect on the morphology and stability of nanobubbles. The bubble response is strongly dependent on both field frequency and amplitude, exhibiting elongation, anisotropic collapse, and isotropic recovery as the frequency increases. We further show that while the direct effect of dipole reorientation on the orientation of interfacial water molecules at high frequencies is relatively small, it substantially enhances rotational kinetic energy. This increased molecular rotation induces frequency-dependent, anisotropic disruption of hydrogen bonds, which in turn elevates structural stress and reduces surface tension. As a result, the nanobubble structure is destabilized, leading to varying degrees of deformation or collapse. Overall, this work elucidates the microscopic mechanisms underlying Terahertz-field-induced nanobubble dynamics and provides theoretical guidance for controlling bubble morphology and interfacial energy transfer via external electric fields.