We demonstrate a purely mechanical technique for enhancing evaporation-driven convective deposition of particle monolayers from suspension. Lateral vibration in the deposition direction results in monolayer deposition at faster speeds, over a wider range of withdraw rates, and with higher order versus traditional convective deposition. These enhancements and phenomena are a result of variation in the thin film, where capillary interactions result in self-assembly by dynamically changing the air-liquid interface. This enhancement in fabricating ordered particle thin films may enable development of optical and biological applications and efforts to scale-up this process for commercial application. V

Binary convective deposition of silica/polystyrene under a number of different operating conditions is used to form nanoporous polymeric membranes with uniform and repeatable pore size throughout and across the membrane. One micrometer silica microspheres and 100 nm PS nanoparticles are codeposited from suspension under conditions where respective constituent fluxes are matched. Membrane thickness is controlled through single and consecutive monolayer and multilayer depositions. Consecutive monolayer depositions result in thin films with highest order and packing. Polymeric membranes were successfully fabricated from a continuous thin film by etching the SiO(2) microspheres with HF or KOH. Etching proceeds radially inward from the polymer-oxide interface suggesting that etchant/thin film interfacial energies help create the initial etching profile and drastically increase the overall etching rate. These membranes, of tunable pore size and functionality, will be ideal for targeted bioseparations specifically in the partition of pathogen particles out of blood suspensions.

Rapid convective deposition is an effective method for depositing well-ordered monolayers from monodisperse suspensions; however, much less is known about polydisperse suspension deposition. The addition of a much smaller species can enhance deposition by extending the range of ordered deposition and can induce instability, producing stripes and other complex morphologies. By considering relative species flux, we predict the volume fraction ratio of smaller to larger constituents necessary for steady well-ordered deposition. Experiments varying the 1 microm microsphere and 100 nm nanoparticle concentrations exhibit an optimum nanoparticle to microsphere volume fraction ratio at moderate volume fractions that agrees well with theory. Average local bond order and surface density characterize crystallinity and coverage, respectively. At lower microsphere volume fraction, monolayer crystallinity is optimized at a constant nanoparticle volume fraction of 0.04. At lower-than-optimum nanoparticle concentrations for each microsphere concentration, instability occurs and alternating stripes of monolayer and submonolayer morphologies form. At higher-than-optimum nanoparticle concentration, the microspheres become disordered and/or form multilayer regions. Additionally, the degree of microsphere burial in deposited nanoparticles depends solely on nanoparticle concentration.

Rapid convective deposition is used to assemble nanoparticle coatings from suspension, with controllable thickness. Varying film thickness generates stress-induced linear cracks with highly monodisperse spacing. Film thickness is controlled through mechanical means, suspension volume fraction, and the use of applied thermal gradients. These cracks extend in the deposition direction, and a uniform crack spacing from 2 to 160μm is observed. The nanoparticle film thickness is the relevant length scale for hydrodynamic flow, and films will crack with this spacing, in a characteristic manner to minimize the system energy and capillary stresses. As expected from this energy minimization problem and relevant theory, the correlation between coating thickness and crack spacing is highly linear. Because this process is continuous, continuous cracks have potential as a high-throughput method of fabricating nanoscale channels for microfluidics and MEMS.