Facilitated transport enhances spray layer-by-layer assembly of oppositely charged nanoparticles

Abstract

We investigate the fundamental mechanism of spray-assisted layer-by-layer (LbL) assembly of oppositely charged silica nanoparticles. Alteration of the major operating parameters such as suspension concentration, spray flow rate, and spray duration allows us to develop a kinetic model for spray-assisted LbL deposition. The spray-deposition mechanism is broken down into two sequential mass transport steps: bulk spray flux to the substrate surface followed by random motion of nanoparticles through a thin liquid film that adheres to the substrate throughout the spray procedure. We demonstrate that the second transport step limits the overall deposition rate, and we examine the importance of a convective driving force in accelerating this random motion close to the substrate by controlling the depth of the liquid film atop the substrate. Finally, we generalize the idea of convective acceleration and find that sufficient agitation can be used to enhance the rate of dip layer-by-layer assembly as well.