Influence of Carrier Gas Flow Rate, Laser Repetition Rate, and Fluence on the Size Distribution and Number of Nanoparticles Generated Per Laser Shot During Paint Laser Ablation

摘要

This study focuses on the influence of three operating parameters (gas flow rate, laser repetition rate, and fluence) on the number and size distributions of nanoparticles generated by laser ablation of acrylic paint. These particles, produced by gas-to-particle conversion of vapors generated by polymer vaporization, can have a spherical shape with a 16 nm diameter (called primary particles) but most of them are aggregated primary particles. The most critical parameter is the gas (air) flow rate in the ablation cell. Indeed, the total number of nanoparticles produced per shot increases with the air flow rate, whereas the aggregate size decreases. Indeed, the gas flow rate controls the transit time and the related aggregation duration, which decrease with increasing flow rates. The influence of the air flow rate on the nanoparticle total number produced per shot can be attributed to the evolution of the particle residence time in the setup with the flow rate. In order to validate this point, the setup has been modeled (model based on the Smoluchowski coagulation equations). The model has shown that the primary particle aggregation mainly takes place in a sphere of a few millimetres in diameter. This sphere varies in volume with the laser fluence but does not depend on the air flow rate in the cell. Moreover, the nanoparticle final number per shot does not depend on the primary particle initial number per shot but only on the size of the interaction volume, which is related to laser fluence.