Thin Film Deposition of Conducting Polymers and Carbon Allotropes via Interfacial Solution Processing and Evaporative Vapor Phase Polymerization
A new solution processing technique is developed for depositing continuously conductive transparent thin films comprised of conducting polymer nanostructures. The deposition mechanism is driven by interfacial surface tension gradients leading to rapid directional fluid flow known as the Marangoni effect. This technique is a universal solution to thin film deposition for coating any type of substrate at ambient conditions within seconds. The versatility of this method of deposition is further explored utilizing Pickering emulsions of carbon allotropes to produce transparent conductive coatings. Film morphology and electrical properties of carbon nanotubes and sheets of both graphite oxide and chemically converted graphene are controlled by solution processing at the liquid/liquid interface. This dissertation reports on harnessing directional fluid flow to afford a simple and scalable thin film deposition technique for both organic and inorganic nanostructured semiconductors. Substrate directed thin film deposition is engineered by forming a liquid-liquid interface on the surface of a target substrate and is accomplished by matching the surface energy of a substrate to the surface tension of solvents utilized for emulsifying solid nanostructures. Flexible substrates such as poly(ethylene terephthalate) and polyvinyl chloride are coated directly by combining solid nanostructured semiconductors, water and a fluorocarbon. The extremely low surface tension of a fluorinated fluid leads to the wetting of plastics and provides a liquid layer on the surface of a plastic substrate that serves as an anchoring layer for attachment of solids and formation of a continuous and conductive thin film. Spreading is shown in a supplementary movie submitted with this dissertation.
A new technique for the synthesis of poly(3,4-ethylenedioxythiophene) nanofibers by vapor polymerization of an aqueous droplet of iron(III) chloride without a template is also demonstrated. Nanofibers of high aspect ratio of this conducting polymer could only previously be synthesized with the aid of templating agents such as pre-electrospun nanofibers. Now, by inducing a constant contact area mode of evaporation, polymer morphology is controlled and vapor polymerization of an oxidant droplet results in a highly conductive, stable and robust thick film comprised of intrinsic one-dimensional vertically directed anisotropic nanostructures of high aspect ratio.