Date of Award
Doctor of Philosophy (PhD)
Micro and Nanoscale Systems
Taking into consideration two different types of surfaces, this dissertation proposes techniques to coat the surface of natural fibers and oil-water interfaces by spontaneous self-assembly of halloysite clay nanotubes. The material of choice, halloysite clay, is a widely available natural resource and can be used after minimal processing. In regards to chemical composition, halloysite clay resembles aluminosilicate mineral kaolin; physically, a defect in the crystal structure ordering causes the sheets of kaolinite to roll into halloysite nanotubes. The dimensions of halloysite nanotubes are dependent on the source, but generally vary from 200 nm to 3 µm in length, 100-150 nm for the outer width and 10-20 nm diameter for the inner lumen. The inner lumen is lined with a gibbsite-like array of Al-OH groups and the outer surface consists of Si-O-Si linkages. The differing chemistries of the inner and outer surfaces make halloysite a candidate for selective modifications.
The coating strategies thus proposed in the text are extended and often designed for specific applications. The purpose of oil-water interface coating is to design environment-friendly mitigation solutions for oceanic oil spills and bioremediation of crude oil. Halloysite clay can act as solid stabilizers at an oil-water interface and form Pickering emulsions. The quality and stability of such emulsions were enhanced by grafting silane molecules onto the surface siloxane groups of halloysite. The silane molecules have long alkyl residues which render the halloysite after grafting, hydrophobic and increase their contact with the crude oil phase of the Pickering emulsions. Growth studies of a hydrocarbon degrading bacteria, Alcanivorax borkumensis (a species endemic to the Gulf of Mexico), in the presence of halloysite Pickering emulsions revealed the positive effect clay nanotubes have on the proliferation of similar bacteria. The materials used for forming Pickering emulsions have been developed into an extended application for encapsulation and roomtemperature storage vehicle for hydrocarbon-degrading bacteria. The assembly of clay nanotubes on oil droplets to give emulsion was reversed to have highly hydrophobic halloysite (with contact angle > 110°) encapsulate a droplet of water. The resulting architecture, termed as liquid marbles, are designed to store and revive oil-degrading bacteria within them and aid the formation of Pickering emulsion as a synergistic approach for oil spill bioremediation. Hair, as a natural fiber, is studied in detail as a substrate for self-assembly.
Halloysite coating on the hair surface was developed to be applied as an efficient, harmless and rapid-acting drug-delivery system directly to the hair. A combination of modifications to the self-assembly process and the type of chemical loaded inside the lumen have resulted in strategies for hair coloring, anti-lice and hair loss control treatments. The method described to alter the surface of hair is ubiquitous in terms of the solvent used and source of the hair; it can be applied to animals like cats, dogs and horses as well can be extended to coat natural textile fibers like silk and wool. The applications thus discussed and examined were set as the goals of the research conducted as a part of the Doctoral program.
Panchal, Abhishek, "" (2018). Dissertation. 1.