Influence of optical microcavitation on fragmentation and defragmentation processes of carbon nanoparticle agglomerates under the action of nanosecond laser pulses

Subject of study. The nonlinear process of transforming carbon black nanoparticle agglomerates (CBNPAs) in a biological liquid medium under the influence of nanosecond laser radiation was examined. Aim of study. The aim was to determine the role of optical microcavitation, in combination with accumulative effects, in the competitive processes of fragmentation and defragmentation of CBNPAs in a liquid medium exposed to a series of nanosecond laser pulses in the near-infrared range. Method. Optical microscopy, combined with software-based image processing, was performed on phantom samples irradiated under various laser regimes. Main results. The nonlinear contribution of accumulative heating to structural changes in CBNPAs was experimentally established. A range of parameters—namely, the count of laser pulses and their repetition rate—was identified, within which fragmentation-to-defragmentation transition occurred. Mechanisms of fragmentation and defragmentation of CBNPAs were proposed. Practical significance. The studied regularities are crucial for optimizing laser processing regimes of CBNPAs in liquid media, including biological ones.