Browsing by Subject "tunable"

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    Tunable Synthesis and Characterization of Oleo-Furan Sulfonate Surfactants from Renewable Furan and Fatty Acids
    (2018-05) Joseph, Kristeen Esther
    An important advance in fluid surface control was the amphiphilic surfactant composed of coupled molecular structures (i.e., hydrophilic and hydrophobic) to reduce surface tension between two distinct fluid phases. Surfactants are widely used in household detergents, cleaners, emulsifiers, foaming agents, and personal care products. Anionic surfactants constitute 50% of the $30 billion global surfactant industry and are widely used in household detergents, and personal care products. Linear alkylbenzene sulfonates (LAS) are widely used due to their low cost and high detergency. Current LAS production methods rely on toxic catalysts and petrochemical-based constituents, such as benzene and long chain hydrocarbons. The reaction has low selectivity to the prescribed linear structure thereby rendering minimal control over the desired composition and properties. Additionally, implementation of simple surfactants such as LAS has been hindered by the broad range of applications in water containing alkaline earth metals (i.e., hard water), which disrupt surfactant function and require extensive use of undesirable and expensive chelating additives. Despite years of technology development, most large-volume surfactants are made from petrochemical sources, while efforts to make renewable surfactants are focused on making existing surfactant structures from renewable sources. In this work, we demonstrate a new surfactant based on the natural structure and chemistry of plant-based oils and sugars with superior function and suitability as a replacement to petrochemicals. Furans obtained from lignocellulosic biomass can be acylated with triglyceride-derived fatty acids and anhydrides in the presence of a heterogenous zeolite catalyst. The results obtained for the reaction of lauric anhydride with furan show that different pore sizes, structures and acidity of zeolites result in varying acylation activity. Preliminary kinetic studies of the indirect acylation using anhydrides provide insight into reaction orders and product inhibition resulting in lowering of catalytic activity. Following acylation, the molecule can be upgraded via several independent and sequential chemistries such as etherification, hydrogenation and aldol condensation and finally subjected to sulfonation to yield surfactant molecules termed as oleo-furan sulfonates (OFS) in high yield. Evaluation of surfactant performance of OFS revealed hundredfold better detergency and stability in hard water conditions in comparison with petroleum-derived counterparts. The synthesis of OFS molecules is, highly tunable and selective where the number of carbon atoms in the linear or branched chain can be easily varied without compromising on reaction yields to achieve desired surfactant properties.
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    Tuning the Chiral Optical Response of Metamaterial and Metamaterial-Semiconductor Nanocrystal Hybrid Systems
    (2020-06) Pachidis, Pavlos
    Chiral metamaterials have been proposed as a promising platform for exotic optoelectronic applications such as ultrasensitive sensors, 3D displays, and ultrafast optical circuits. The functionality of such devices depends on their ability to dynamically change their optical response when a stimulus is applied. However, there are few examples and strategies for designing chiral systems with dynamically tunable optical response without necessitating reconfiguration of the chiral assembly. This thesis presents nanostructures with chiroptical response that can be tuned by modifying the refractive index of non-metallic components, and examines the effect of different design parameters on both circular dichroism and circularly polarized photoluminescence (PL). We show a chiral metamaterial system with metallic and dielectric components, where the refractive index of the dielectric component tunes the dissymmetry in transmission of right and left circularly polarized light (RCP, LCP). We then study the polarization of PL from chiral gold nanorod dimer arrays coated with poly(lauryl methacrylate) - CdSe/CdS quantum dot (QD) composite films. For these studies, we constructed a Fourier space polarimeter and demonstrated how changing the pitch of the periodic array, altering the luminescent material, introducing a dielectric spacer layer, and modulating the refractive index of the underlying substrate affects the handedness and directionality of the PL of the QD film. Finally, we show using finite-difference time-domain simulations that the placement of luminescent nanostructures within the unit cell of metallic arrays leads to enhanced degrees of circularly polarized PL compared to luminescent films that coat the metallic arrays uniformly. In this fashion, metamaterials with highly tailored directionality and polarization of PL can be designed and built. We fabricate assemblies of gold nanorods with QD nanopillars as well as assemblies of nanostructured QD solids via direct-write electron beam lithography, and show that these assemblies exhibit substantial chiroptical response. The results of this thesis encourage the integration of dielectric, phase change, or other materials with switchable optical properties in the design of chiral optical metamaterials, and expand the range of architectures and strategies for dynamically tunable chiroptical properties.