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ItemMicellar and liquid crystalline phases of surfactant/Pluronic mixtures studied by SANS(Georgia Institute of Technology, 2019-10-04) Zhou, BoyangThe phase behaviours of Pluronic L62 in aqueous solutions in the presence of Aerosol-OT(AOT) molecules was investigated by small angle neutron scattering (SANS). The presence of AOT was found to significantly change the micellization phenomenon of L62 micelles in aqueous solutions, including their critical micelle temperature (CMT), global size, and asphericity. The origin of these observations is attributed to the complexation between the neutral L62 surfactants and the ionic AOT molecules: The ionic groups of AOT renders the molecular charge to the aggregates of L62/AOT. On the context on molecular charge, we address the phase properties of L62/AOT complexation such as the critical micelle temperature, global size, asphericity revealed by SANS at different controlled thermodynamic conditions.
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ItemIntegration of optical structures with chiral nanocellulose films(Georgia Institute of Technology, 2019-07-23) Yu, ShengtaoGeneration of circularly polarized (CP) light via cellulose nanocrystals (CNC) has demonstrated great potential for next generation of chiroptical materials, thanks to the abundance, cost-effective preparation, as well as the retained chiral liquid crystal ordering in solid form. To enhance the chiroptical properties of CNC film, a convenient strategy capable of integrating both diffractive and refractive optical structures is developed based on top-down lithographic techniques and bottom-up evaporation-induced self-assembly. The feasibility of such strategy is proved by a few optical structures including photonic gratings, photonic crystals and micro-lenses. The successful integration of these extrinsic structures with intrinsic chiral structure of CNC is evidenced by preservation of helical stacking structure of CNC as well as a good registration of features size down to sub-micron level with uniformity across large area on the film surface. As a result, a combination of more accurate and sharper structural color, light focusing capability as well as enhanced circular dichroism is observed, indicating great potential in advanced optical systems based-on CP light. This is the first study to manipulate and enhance the chiroptical properties of CNC with artificial photonic structures, while the unconventional hybrid strategy demonstrates a fledgling, yet promising method for development of hierarchical biophotonic materials in general.
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ItemStructural investigation of silk fibroin-based membranes(Georgia Institute of Technology, 2014-04-09) Wallet, BrettSilk fibroin has created a surge of interest for use as organic material due to its optical transparency, biocompatibility, biodegradability, and excellent physical properties. However, the implementation of silk films and structures into biomedical and sensing devices has been relatively low due to a lack of understanding of the mechanisms involved in such implementation. Increasing need for multifunctional high-performance organic materials has caused an emphasis on the ability of researchers to spatiotemporally pattern and control the structure and consequently functional properties of materials. Silk fibroin displays high potential for use as a controllable biomaterial that can be formed into a myriad of different structures for various applications. By implementation of an aqueous silk solution approach combining various fabrication techniques, several different pristine-silk and silk-composite membranes have been developed to investigate the importance of internal structuring. Different methods of investigation include: 1) incorporation of reinforcing nanoparticles within the silk matrix; 2) neutron reflectivity measurements of ultrathin silk films; 3) film patterning with nanoscale features followed by boundary organized surface mineralization of inorganic nanoparticles. The ultimate goal will be to provide fundamental data assisting in an increased knowledge of silk fibroin-based membranes and the effect of secondary structures on properties of interest.
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ItemProperties of confinedpNIPAM-co-AAC microgels(Georgia Institute of Technology, 2011-04-05) Marczewski, KamilTunable nanostructures have many important uses in thin film applications. Tunability can be achieved by creating a film that has features that respond to external stimuli, such as temperature, humidity, or pH. However, the response can vary greatly between a confined and unconfined case. In the case of confined materials, this response can be greatly reduced, even completely suppressed, which indicates that separate studies must be conducted on confined states in order to better understand their use for real applications. Microgels have been previously shown to have exceptional responsive properties that depend on their chemical structure and synthesis. Unlike solid thin hydrogel films that respond on the order of hours, microgels arrange on a surface with no external force and create a highly porous layer which responds rapidly, on the order of minutes, to outside stimuli. These properties make microgels a promising candidate for use in tunable thin films. Although the responsive properties of microgels have been extensively studied in solution and unconfined films, this is not indicative of conditions that would most likely have the microgels placed between two stiffer layers of material. Microgels have been shown to respond to glucose concentration, temperature, pH, and light. One well-studied microgel is poly-N-isopropylacrylamide copolymerized with Acrylic Acid (pNIPAM-co-AAC). These microgels use the thermal response of pNIPAM combined with the pH sensitivity of pAAC to create a dually-responsive material. To study the effects of confinement on pNIPAM-co-AAC microgels, we encapsulated these particles within bi-layers of poly(allylamine hydrochloride)-poly(sodium 4-styrenesulfonate) (PAH-PSS) in order to simulate their response within a polyelectrolyte material. Our samples were prepared with a method called tilt-drying, which creates a microgel concentration gradient. This allowed us to study both the confinement caused by the multi-layered film as well as the effects of microgels on each other. Our results have shown that the change in particle height is unaffected by the concentration of the film, but the thermal response of pNIPAM-co-AAC microgels is significantly suppressed by the encapsulation of microgels into nanoscale layers.
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ItemBiomineralization of inorganic nanostructures using protein surfaces(Georgia Institute of Technology, 2008-04-01) Bergman, Kathryn N.In nature, organisms have long been able to create elaborate mineral structures at ambient temperatures. From a materials science and engineering perspective, favorable properties emerge when the synthesis process can be controlled at finer levels. New strategies in materials chemistry synthesis has been inspired by biomineralization: biomimetics. In this work, silk fibroin films were used to synthesize gold nanoparticles room temperature by soaking a free standing 15nm silk film in HAuCl4. Particles ranged in size and shape from 5nm spheres to 105nm hexagons. Secondly, a film of ZnO1 peptide (ZnO selectively binding peptide) was successfully formed by drop casting on both silk and polystyrene surfaces. Using a HMT + Zn(NO3)2 system for ZnO wet chemical deposition, rods were formed on the peptide surface. Changing solution concentration and growth time affected the density and size of the nanorods. Spin coating a 3nm peptide film reduced the roughness to <1nm, upon which an array of vertical ZnO rods with controllable density was synthesized.