Growth of nanoparticles in dynamic plasma

Coagulation growth kinetics of nanoparticles in plasma is affected by interparticle electrostatic forces due to the charging phenomenon. In stationary plasmas, unipolar charging of particles results in retardation of particle growth and may result in a limitation on particle size. We demonstrate the opposite effect of enhanced particle growth in atmospheric pressure nonstationary arc discharge. Modeling of the nanoparticle growth kinetics reveals the formation of a bipolar charge distribution. As a result, reversed (attractive) Coulomb forces promote the formation of micrometer-size particles in a millisecond timescale as observed in experiment.

Figure 1

Schematic of (a) the experimental setup, (b) arc motion, and (c) particle interactions.

Figure 2

Radial distribution of plasma density and temperature, and gas temperature in the arc. Profiles are calculated using ansys cfx code.

Figure 3

Two selected frames (with 660-$\mu \mathrm{s}$ delay) recorded during the arc at $60000$ frames/s. The video resolution is $22\mu \mathrm{m}{\mathrm{pixel}}^{-1}$ and the frame exposure time 5 $\mu \mathrm{s}$. Particles of micron scale are encircled in (b) and schematically shown in the cartoon on the right.

Figure 4

Time evolution of (a) temperature and (b) potential of particles and (c) enhancement factor $\gamma$ between selected pairs of particles closest to the arc distance. Model parameters (electron density $n_e$, temperature $T_e$, gas temperature $T_{\mathrm{gas}}$, and distance to the arc $r=r_{\min }$) used in modeling are shown in (b).