Modelling the electrophoretically-enhanced in-flame deposition of carbon nanoparticles

Flame synthesis of Carbon NanoParticle (CNP) films is gaining strong interest for novel industrial applications because of the easy tuning of the operating conditions that enables accurate control of the chemical and physical properties of the produced CNPs. This work proposes a novelty in the synthesis of CNP films, namely the possibility of applying electric fields in flame to trigger electrophoretic deposition phenomena. In this way, it is possible to add another degree of freedom to the harvesting process and potentially modify the properties of the CNP films, without changing the operating flame conditions. To investigate the physical mechanisms governing the thermo-electrophoretic deposition of CNPs, a numerical model to simulate the particle dynamics close to the collecting substrate has been developed, and experiments have been carried out to provide highly controlled test conditions that can be used to support model validation. The experimental results consist of Atomic Force Microscopy (AFM) measurements to determine the number of particles deposited after a controlled harvesting condition as a function of the applied electrophoretic force, imposed on the substrate by means of a DC voltage varied from 0 to -3kV. The AFM shows that the amount of deposited material increases up to six times when passing from an uncharged to the -3kV charged case. The model predictions are highly consistent with the AFM measurements and pointed out that the electric field in flame significantly alters the CNP deposition velocities and impact angles, which are likely to affect the properties of the film.