Optimization and application of nanocomposite coatings for protection and functionalization
Creators: name: Grzenda, Michael Joseph
Publisher: name: No Publisher Supplied
Year: 2023

description: Coatings are efficient routes to upgrade structures and devices. They can be multi-functional, providing both protection and utility. However, when dealing with electronic devices, the electronic behavior of the coating materials becomes of the utmost importance. In this work, we optimize coating materials both to protect electronic devices from environmental damage, and to upgrade existing devices to add new functionality, all while controlling the charge mobility in the material. We approach this problem in two ways, through controlling the nanoparticle content in polymer-nanoparticle composites, and through control of the material mobility. More specifically, we seek to design and implement materials that have high resistivity and low permittivity during processing, though in some instances we seek to change those properties post-processing. For the nanocomposites, we focus on conductive particles as fillers due to their other desirable properties, such as high conductivity or functionality. We must therefore consider the percolation of these particles in order to prevent the formation of conductive networks that would otherwise disrupt the low permittivity and high resistivity of the coatings. In our first aim, we seek to design and apply an epoxy-based nanocomposite for light-weight protection of electronics on an air-to-deep sea vehicle (Chapter 2). Our composite material is composed of three phases, epoxy, oil, and graphene, and our goal is to optimize these phases to allow for easily processed, mechanically robust, light-weight protection. Importantly, we also use the graphene particles to increase the thermal conductivity of the material without creating an electrically percolated network, and our efforts are discussed in light of percolation theory. With these goals in mind, we fully characterize our nanocomposite coating, compare it to competing material, and finally demonstrate its application to electronics in both bench-top conditions and actual deep-sea missions.In our second aim, we seek to deposit nanoparticles with targeted micron-scale precision using electrospray deposition (ESD) with the goal of device fabrication and functionalization. However, micropatterning with ESD has never been fully explored and contrasted across spray regimes. These spray regimes are dependent on charge mobility which is in turn highly dependent on material mobility. Therefore in Chapter 3, in lieu of optimizing filler content, we focus on polymeric materials and optimize coating mobility in the context of micron-scale patterning. This is achieved through spray onto micron-scale test patterns and analysis of the specificity, density, and height of the patterned deposits. Ultimately it was seen that the self-limiting spray regime (where both material and charge mobility is low) is necessary for highly uniform and controlled patterning. Finally in Chapter 4, we synthesize the results from the previous two chapters as we aim to deposit conductive nanoparticles in the self-limiting regime onto micron-scale features via composites. From our results in Chapter 3, we see that this requires very-low charge mobility in our films. To achieve this, we must again work with sub-percolation composites as we did in Chapter 2. These composites are similarly composed of a polymer phase, an inorganic flake-like particle, and a non-solid phase (methylcellulose, MXene, and porosity respectively), and the implications for percolation behavior are again explored. We turn to our test-patterns to quantify this system, this time measuring feature overgrowth growth via optical microscopy. Ultimately, we show that sub-percolation, self-limiting sprays can be achieved by optimizing particle size, shape, and concentration. We use this knowledge to functionalize interdigitated electrodes with features and spacings as low as 50 microns, and a substantial increase in capacitance was measured.