Research On Mechanism And Effect Of Photo- Breakdown Induced Cavitation In Gold Nanoparticles Solution

Under the excitation of a specific wavelength of laser,gold nanoparticles have unique physical and chemical properties,especially the light collection and light amplification ability of gold nanoparticles,which are widely used in cell therapy and biological image enhancement in the field of biomedicine and solar energy collection and micro-nano processing in engineering field.The interaction mechanism between laser and gold nanoparticles is complex,and the current studies are mainly focused on plasmon resonance effect and photothermal transfer effect,as well as the formation mechanism and phenomenon of cavitation induced by thermally induced evaporation induced by low energy laser.There are few studies on the phenomenon of cavitation induced by photo-induced breakdown induced by high-energy laser.The study on the mechanism and effect of photo-induced breakdown cavitation in gold nanoparticles solution,on the one hand,can improve the interaction mechanism between laser and gold nanoparticles,on the other hand,the material recombination in the process of photo-induced breakdown-induced cavitation,the acoustic radiation associated with bubble pulsation and collapse can broaden its application in the fields of water treatment,photoacoustic transformation and surface modification.In addition,the cavitation induced by light breakdown of gold nanoparticles also has the advantages of low breakdown threshold and accurate induction position.In this paper,the nanosecond pulse laser with wavelength 532 nm is used to study the effect of gold nanoparticles on laser cavitation characteristics by simulation and experiment.It is found that the light field enhancement and cavitation intensity increase related to the particle characteristics.The modulation of the particle size and distribution of gold nanoparticles on the incident laser light field was simulated by FDTD.The dynamic sequence diagram of laser-induced cavitation in gold nanoparticles solution was captured by high-speed camera,and the changes of free radical content and sound pressure signal caused by cavitation in methylene blue solution were measured to quantitatively judge the effect of gold nanoparticles on laser cavitation intensity.According to the comparative analysis of wall morphology and composition,we explore the possibility of photo-induced breakdown cavitation in gold nanoparticles solution for material surface modification.The contents of the study are as follows:(1)Based on the local surface plasmon resonance effect and Michaelis theory,according to the photoheat transfer equation of nanoparticles and the theory of liquid explosion,we derive the pulsation equation,shock wave transport equation and particle motion equation of cavitation induced by photobreakdown.It is concluded that gold nanoparticles significantly reduce the laser breakdown threshold in liquid.(2)We simulate and analyze the light field distribution around gold nanoparticles,and calculate the optical absorption and amplification ability of gold nanoparticles under different particle sizes and particle concentrations.The effects of the characteristics of gold nanoparticles on the initiation,pulsation and collapse of cavitation induced by photo-induced breakdown were obtained.(3)We experimentally studied the characteristics of photobreakdown-induced cavitation in gold nanoparticles solution under the action of 532 nm light source.The dynamic sequence diagrams of photobreakdown-induced cavitation on the liquid surface and inside the solution were captured by a high-speed camera.By comparing the number and size of cavitation in distilled water and solutions with different gold nanoparticles concentration,we obtained the law that the laser breakdown effect was affected by the size and concentration of gold nanoparticles,and found the relationship between bubble size and focus position.The content of free radicals generated by laser cavitation was characterized by the concentration change of methylene blue.It was found that the concentration of free radicals produced by laser-induced cavitation in gold nanoparticles solution was significantly higher than that in distilled water,and the increase was related to the laser energy and the number of actions.The sound pressure signal measured by hydrophone is used to characterize the shock wave amplitude of laser cavitation.Compared with distilled water,the number and amplitude of shock wave induced by laser cavitation in gold nanoparticle solution are more and uniform,but the duration is short and the intensity is small.(4)We experimentally study the effect of the wall of gold nanoparticles on the characteristics of photo-induced breakdown cavitation.Compared with the surface morphology and composition analysis of the wall in distilled water,the strong absorption of cash particles leads to the decrease of the action area of the wall,showing a ripple shape.And there are a large number of micro-nano-scale pore distribution.The gold elements exist in the center and edge of the laser action region,but the distribution is uneven,which is related to the concentration of gold nanoparticles and laser energy.The material resistance after cavitation in gold nanoparticles solution becomes smaller under external 532 nm laser irradiation,which is related to laser scanning frequency,gold nanoparticles concentration and single pulse laser energy,while the surface resistance in distilled water does not change.