| dc.description.abstract | Achieving desired nanoparticle (NP) morphologies upon evaporation of particle-laden droplets is very challenging due to the complex behavior involving particle-particle, particle-substrate, and particle-fluid interactions. Controlling the patterns of deposited NPs can be exploited to fabricate tailored nanostructures that add functionality and engineer the properties of the manufactured components. Nanoparticle spray deposition is an effective method of delivering particle-laden droplets that place desired particles on substrate. This technique finds numerous applications in electronics, food, drug, manufacturing, and energy industries. Various spray deposition techniques such as spray drying, thermal, and electrosprays are common practice for NP deposition. However, they all lack the required precision in controlling the droplet attributes as atomization is inherently a random process. In addition, NPs tend to accumulate along the pinned droplet contact lines during droplet evaporation, a phenomenon known as the coffee ring effect (CRE). Eliminating or exploiting CRE requires costly and multi-step processes. Moreover, NPs of interest in engineering applications are typically hydrophobic and tend to agglomerate in water, and thus cannot be directly sprayed. A novel nanoparticle spray deposition system is designed and built by integrating supercritical CO2 assisted atomization of aqueous nanoparticle suspensions. The supercritical CO2 boosts liquid atomization by reducing the liquid surface tension and enabling dissolved gas atomization mechanisms. The combined effects results in controllable creation of micron-size droplets with a narrow size distribution that directly affect the evaporation rate which in turn dictates the NP self-assembly mechanism. A nanoparticle-agnostic approach is introduced that allows the fabrication of multi-material nanostructures with precisely engineered patterns. Evaporative droplets of aqueous suspensions of Carbon Nanotubes, Graphene Nanoplatelets and Boron Nitride Nanotubes representing NPs of different elemental composition, sizes and shapes are investigated. Cellulose nanocrystal (CNC) is used as a platform to make hybrid systems of CNC and the secondary NP. Fundamental understanding of repulsive-attractive interactions in this hybrid system is capitalized to explain their effects on the final pattern. It is shown that formation and thickness of deposited patterns of CNC-bonded NPs after evaporation of droplets depends only on the concentration and mass ratio of the NPs and not their shape and size or NP. | |
