Microjets via Laser-Induced Tandem Bubble for Controlling Crystallization in a Micro-capillary

Abstract

Understanding and controlling primary nucleation remains one of the central challenges in crystallization. Nucleation governs the physicochemical, optical, and mechanical properties of the resulting crystals. In this thesis, we investigate a novel pathway for inducing nucleation in supersaturated solutions using the hydrodynamic interaction of laser-induced tandem thermocavitation bubbles confined inside a microcapillary. When two cavitation bubbles are generated in antiphase, their asymmetric pressure fields give rise to micron-scale liquid microjets with velocities far exceeding those produced by single-bubble events. These jets penetrate the primary bubble interface, causing localized evaporation, strong solute redistribution, and transient supersaturation spikes. Using supersaturated aqueous potassium permanganate (KMnO₄) as a model system, we demonstrate that crystallization occurs exclusively under tandem-bubble conditions that produce a high-velocity piercing jet, whereas single-bubble cavitation—even at twice the laser energy—fails to nucleate crystals. The results reveal a clear correlation between jet velocity and nucleation probability, highlighting shear-driven solute transport and microjet-induced evaporation as the dominant mechanisms triggering nucleation. This work establishes microjet-mediated crystallization as a physically grounded and a relatively more energy-efficient alternative to conventional non-photochemical laser-induced nucleation mechanisms, with potential applications in controlled crystallization, microfluidic processing and pharmaceutical manufacturing.