Fig. 6
From: Substrate geometry modulates self-assembly and collection of plasma polymerized nanoparticles
Dynamics of plasma polymerized nanoparticles (PPN). The schematic compares the dynamics of PPN in the presence of flat two-dimensional and well-shaped three-dimensional substrates. As the particles are negatively charged in the plasma, they feel an electrostatic force (Fe) in the opposite direction to the electric field, as indicated by the vectors labeled -Efield and repel one another. When they move out of the plasma into regions depleted of electrons and richer in ions, they lose their negative charge and become prone to aggregation when present in high densities. In the presence of a flat substrate, PPN levitate in vertical equilibrium positions near the plasma sheath above the flat substrate. The net drag force (with a horizontal component), primarily due to the net neutral drag (Fn) arising from the gas flow around the substrate towards the pumping system and the thermophoretic force (Ft) due to temperature gradients (ΔT) between the plasma bulk (370 K) and the chamber’s walls (300 K) drag the particles outside the substrate region, resulting in the deposition of a coating with a low number of particles. In the presence of well-shaped collectors, PPN move inside the well due to expansion of the plasma into the well and confinement by electric fields at the perimeter of the wells. The net drag force (with a vertical, downwards component for particles closest to the well central axis), and primarily due to the action of Ft and ion drag (Fi) forces, drags trapped particles towards the bottom of the wells. No coating is deposited on the bottom of the well
