(4by) Convective Assembly of Nanoparticles Into Thin Structured Films

Convective nanoparticle film assembly is a simple process whereby particles from dilute liquid suspension assemble onto a substrate. Assembly occurs at the suspension-substrate-air contact line, where particles are carried toward it by convective currents set up in the meniscus region due to liquid evaporation. This process is explored as a potential method for the fabrication of highly ordered (i.e. uniformly oriented) nanocrystal films for application in zeolite membrane technology. Typical results indicate plate-like crystal nanoparticles do tend to orient preferentially in convectively assembled films, but that such films are often patterned (precluding their usefulness as membrane precursors). Specifically, the resulting films tend to have discrete banded morphologies; the bands are almost universally reproducible, and can be quite regular. Banding and film morphologies are studied using spherical nanoparticles, especially in the context of the competing rates of particle assembly and substrate withdrawal (contact line recession). Some attempts at modeling the band spacings are presented, as such descriptions may be helpful in modeling the process itself.