Convective Deposition

A strong interest exists in modifying surfaces to control their physical and chemical characteristics. There is perhaps no easier method of functionalizing a surface than depositing particles having the desired properties for the new material. Likewise, there is no easier way of utilizing discoveries in synthesized functional nanoparticles than developing a process that self-assembles these materials into highly ordered arrays. This scalable nanomanufacturing program aims to develop a continuous process that can be utilized by industry Controlled colloidal and/or nanoparticle deposition on substrates has impacted fields ranging among catalysis, photonics, ceramics, surface biocompatibility, sensors, and adhesion. In many of these applications desired function is highly sensitive to microstructure, e.g. surface density, crystallinity, and orientation of the particulate layers modifying these surfaces. As such, the realization of many modified materials applications demands unprecedentedly fine control over this microstructure.

By drawing a meniscus of a suspension across a substrate, particles drawn into the trailing thin film self-organize and are deposited onto the surface. By controling the thin film dynamics, we are can control the surface morphology and microstructure. We are using multiple novel approaches to enhance and control convective deposition including varying blade angle, depositing binary suspensions, and using mechanical perturbations of the substrate.

Binary Deposition

In essentially all of our applications, we now co-deposit the primary particles of interest with a smaller species to increase the quality of the deposited particle monolayer. Nanoparticles reduce evaporation at the edges and alter the hydrodynamic interactions of particles entering the thin film. However, we discovered a new instability in film formation when the flux of nanoparticles and microspheres are not balanced (see below). This technique is now used regularly in fabrication of microlens arrays and membranes.