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School of Materials Science and Engineering

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College of Engineering

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Publication Search Results

Now showing 1 - 10 of 26

Micellar and liquid crystalline phases of surfactant/Pluronic mixtures studied by SANS

(Georgia Institute of Technology, 2019-10-04) Zhou, Boyang

The 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.
Modulated optical behavior of electrochromic conjugated polymer hybrids

(Georgia Institute of Technology, 2019-07-30) Zhou, Jing

Noble metal nanoparticles and semiconducting quantum dots are promising building blocks for tailoring light-matter interactions at the nanoscale, which find applications in miniaturization of photonic devices, high-throughput optical sensing, and super-resolution imaging. While the optical properties of these inorganic nanoparticles alone have been largely understood, active control of their optical behavior with external fields remains challenging. This dissertation aims to understand and develop novel nanostructured electrochromic conjugated polymer (ECP)/optical inorganic nanoparticle hybrids with electrochemically modulated extinction of noble metal nanoparticles and photoluminescence of semiconducting quantum dots. Important focuses are placed on developing synthetic strategies to fabricate ECP-inorganic nanoparticle hybrids and understanding their optical response as affected by the interfacial assembly, spectral overlap, refractive properties and redox states of ECP during the in-situ electrochemical reaction. As a result of this study, the core-shell hybrid plasmonic nanostructures assembled from a gold nanoparticle core with a various of ECP shells were synthesized by in-situ chemical oxidative polymerization. Different electrochemical plasmon tuning systems have been realized with these hybrids including a dual responsive system with reversible plasmonic shift reaching 150 nm and a system possessing an easily identifiable narrow visible-near infrared absorption band. Next, a manyfold reversible increase in dark-field scattering intensity was revealed for the single hybrid nanoparticle when the conjugated polymer shell was electrochemically switched, which enables the real-time visualization of the redox reaction of conjugated polymer down to single nanoparticle level. Last, by maximizing the spectral change in an ECP with emission of quantum dot in a nanostructured assembly, we demonstrate the electrochemical modulation of quantum dot photoluminescence with a remarkable optical contrast. Overall, we suggest that unique modulated optical behavior that is unachievable in individual components can be accomplished through careful design of spectrally matched hybrid materials. The knowledge obtained in this study can be used to improve the design of high-throughput optical sensors with enhanced sensitivity and scalable, flexible, high-performance displays.
Integration of optical structures with chiral nanocellulose films

(Georgia Institute of Technology, 2019-07-23) Yu, Shengtao

Generation 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.
Biopolymer and synthetic polymer nanocomposite reinforcement via interfacial assembly

(Georgia Institute of Technology, 2019-07-19) Grant, Anise

Protein biopolymer composites bring together the tunability and flexibility of protein matrices and functionality of filler components. Graphene-based biocomposites are particularly popular for design of aqueously processible and strong flexible electronics for sensing, nanowires, and semiconductors. However, a lot of trial and error is required to determine biopolymer and co-constituent chemistry as well as the assembly process needed to capitalize on their synergistic properties. This dissertation identifies non-covalent methods to control interfacial interactions that drive and stabilize assembly of silk fibroin from Bombyx mori silkworm cocoons in order to induce mechanical reinforcement. This work, then shows the cross-applicability of assembly triggers for silk with other semi-crystalline, amphiphilic biopolymers using Humbolt squid sucker ring teeth protein suckerin. And, lastly, synthetic copolymers are used to clarify the role of biopolymer and surface properties on interfacial assembly without post-processing treatments. The main drivers of assembly and interfacial binding studied here include temperature, shear force, hydropathy, and pH. Surface topography and polymer chemistry/conformation were studied concurrently via atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR). This data was supported by simulation to better define assembly mechanisms at the interface of biopolymers and inorganic 2D fillers and their timescales. Then, mechanical characterization via bulging tests and scanning probe microscopy methods (SPM), force distance spectroscopy (FDS) and quantitative nanomechanical mapping (QNM). Mechanical performance is evaluated at the macro and nanoscales using quantitative nanomechanical mapping, FDS, and buckling tests. Overall, this dissertation shows how interfacial assembly driven by the hydrophobic effect can be manipulated using non-covalent means to study to tune mechanical performance. Thus, this work a roadmap for further optimization of biopolymer-based nanocomposites through interface-minded design.
Manipulating photoluminescent properties via spatial control of optically active media within polymer matrices and templates

(Georgia Institute of Technology, 2019-05-21) Smith, Marcus J.

Fundamentally, light management plays a central role in industries such as life science, health, communication, energy, and agriculture. Research involving further understanding and control of light to the benefit of humankind continues to be a driving force for advancing society. Of particular interest is furthering our understanding of light-matter interactions. By controlling these interactions, intriguing optical phenomenon such as directional light modulation and low threshold lasing can be achieved, particularly with photonic assemblies of gain medium. This study focuses on understanding the fundamental aspect of light-matter interactions and propagation in gain medium such as organic dyes, quantum dots (QD), and QD-polymer nanocomposites. Specific emphasis is placed on understanding the QD-polymer interface to realize guided assembly in nanocomposites and on finding the parameters governing optical coupling between nanocomposite structures with particular focus on photonic cavity size, shape, position, and obtaining dynamic tunability. This work provides a scientific framework which demonstrates useful methodologies for designing photonic systems that require control of light-matter interactions including emission, mode activity, and resonator coupling. Specifically, Cd based core and core/shell QDs with different interfacial architectures, including core/shell with sharp interface, and core/graded shell, are investigated to understand dynamic photoluminescence behavior. Core/shell QDs with a CdSe/ZnS composition showed the most dynamic PL behavior with an emission signature that showed semi-reversible recovery behavior based on exposure conditions. Next, an ultrafast crosslinking technique incorporating thiol-ene chemistry was used to realize QD-polymer nanocomposites with high loading, minimal aggregation and optical scattering, and tunable mechanical properties. Finally, lithographic techniques were used to fabricate high resolution templates for whispering gallery mode microsphere resonator assembly, and individual and coupled microdisk resonators with strong coupling. Taking advantage of 3D lithography, with ~200nm resolution, and unique system design we obtain microsphere resonators with sub-100nm gap spacing, equating to strong evanescently coupled resonators. The knowledge obtained herein can be used to aid in the design of robust optical materials with added functionality and tunability for sensing and enhanced light modulation leading to unique optical phenomenon such as directional lasing and unidirectional light propagation.
Plasmonic hybrid nanoconstructs for subwavelength manipulation of optical properties

(Georgia Institute of Technology, 2019-04-24) Zhang, Shuaidi

Plasmonic nanostructures give rise to intriguing optical phenomena such as deep-subwavelength light focusing, precisely tunable scattering/absorption, and super-linearity enhancement. These properties could be harnessed by combining plasmonic components with functional organics into plasmonic hybrid nanoconstructs for practical applications, such as molecular sensing, advanced displays, and photonic logic processing. However, to fully realize the potential of these plasmonic hybrid nanoconstructs, critical questions on fundamental aspects of organic-inorganic assembly and their coupling behavior need to be addressed. This work seeks to understand some of these aspects and fill knowledge gaps regarding the efficient microfabrication and utilization of hybrid plasmonic nanoconstructs. Specifically, an advanced nanoscale characterization method based on scanning probe microscopy and secondary ion mass-spectrometry is developed to monitor the morphological and compositional changes on the surface of plasmonic nanocrystal as ligand exchange reactions proceeds, leading to new discoveries on reaction dynamics. Detailed characterization of nanoparticle distribution in organic matrices and corresponding electrodynamic modeling have also been combined to aid the rational design of a cellulose nanofiber-gold nanorod hybrid surface enhanced Raman spectroscopy based molecular sensing platform that outperforms traditional design by two orders of magnitude. In addition, new discoveries have been made regarding the optical response of electrochromic polymer infused plasmonic nanohole arrays upon complex permittivity modulation: the forward and backward scattering shows drastically different response whose origin is explained by advanced electrodynamic simulation. Finally, using high resolution hyperspectral mapping and high-fidelity sub-nm resolution electrodynamic simulation, we furthered the understanding of coupling between plasmonic nanocrystals and photonic microcavities and proposed a new method that uses the near-field coupling between plasmonic nanoparticle antennas to regulate the optical output of a plasmonic-photonic hybrid cavity, which could lead to extremely compact designs for nanolasers.
Responsive nanostructures for controlled alteration of interfacial properties

(Georgia Institute of Technology, 2017-11-15) Geryak, Ren

Responsive materials are a class of materials that are capable of “intelligently” changing properties upon exposure to a stimulus. Silk ionomers are introduced as a promising candidate of biopolymers that combine the robust, biocompatible properties of silk fibroin with the responsive properties of poly-l-lysine (PL) and poly-l-glutamic acid (PG). These polypeptides can be assembled using the well-known technique of layer-by-layer processing, allowing for the creation of finely tuned nanoscale multilayers coatings, but their properties remain largely unexplored in the literature. Thus, this research explores the properties of silk ionomer multilayers assembled in different geometries, ranging from planar films to three-dimensional microcapsules with the goal of created responsive systems. These silk ionomers are composed of a silk fibroin backbone with a variable degree of grafting with PG (for anionic species) or PL or PL-block- polyethylene glycol (PEG) (for cationic species). Initially, this research is focused on fundamental properties of the silk ionomer multilayer assemblies, such as stiffness, adhesion, and shearing properties. Elastic modulus of the materials is considered to be one of the most important mechanical parameters, but measurements of stiffness for nanoscale films can be challenging. Thus, we studied the applicability of various contact mechanics models to describe the relationship between force distance curves obtained by atomic force microscopy and the stiffness of various polymeric materials. Beyond considerations of tip size, we also examine the critical regions at which various commonly used indenter geometries are valid. Following this, we employed standard AFM probes and colloidal probes coated with covalently bonded silk ionomers to examine the friction and adhesion between silk ionomers layers. This technique allowed us to compare the interactions between silk ionomers of different chemical composition by using multilayer films containing standard silk ionomers or silk ionomers grafted with polyethylene glycol PEG. This led to the unexpected result that the PEG grafted silk ionomers experienced a higher degree of adhesion and a larger friction coefficient compared to the standard silk ionomers. Next, we move to microscale responsive systems based on silk ionomer multilayers. The first of these studies looks at the effect of assembly pH and chemical composition on the ultimate properties of hollow, spherical microcapsules. This study shows that all compositions and processing conditions yield microcapsules that show a substantial change in elastic modulus, swelling, and permeability, with maximum changes in property values (from acidic pH to basic pH) of around a factor of 6, 1.5, and 5, respectively. In addition, it was discovered that the use of acidic pH assembly inverts the permeability response (i.e. causes a drastic reduction in permeability at higher pH), whilst the use of PEG largely damps any observable trend in permeability, without adversely affecting the swelling or elastic modulus responses. In the second part of these studies, we constructed tri-component photopatterned arrays for the purpose of creating self-rolling films. This study demonstrated that the ultimate geometry of the final rolled shape can be tuned by controlling the thickness of various components, due to the creation of a stress mismatch at high pH conditions. Additionally, it was revealed that pH-driven, semi-reversible delamination of silk ionomers from polystyrene exhibited a change in both magnitude and wavelength with the addition of methanol treated silk fibroin as a top layer. Finally, we showcase examples of biologically compatible systems that incorporate non-polymeric materials in order to generate tunable optical behavior. In one study, we fabricated composite nanocellulose-silk fibroin meshes that contained genetically engineered bacteria that acted as chemically sensitive elements with a fluorescent response. The addition of silk fibroin was found to drastically improve the mechanical properties of the cellulose composite structures, safely contain the bacteria to prevent efflux into the medium, and protect the cells from moderate ultraviolet radiation exposure. The final study concludes with the creation of a self-assembled segmented gold-nickel nanorod array used as a responsive element when anchored into a hydrogen-bonded polymer multilayer. Because of the mild tethering conditions and the magnetic nickel component, the nanorods were able to tilt in response to an external magnetic field. This, in turn, allowed for the creation of a never before reported magnetic-plasmonic system capable of continuously-shifting multiple surface polariton scattering peaks (up to 100 nm shifts) with nearly complete reversibility and rapid (<1 s) response times. Overall, this research develops the understanding of the fundamental properties of several different species of silk ionomers and related polymeric materials. This understanding is then utilized to fabricate pH-responsive systems with drastic changes in modulus, permeability, and geometry. In the end, the research prototypes two types of systems with optical responses and chemical/magnetic stimuli, using materials that are chemically (i.e. silk fibroin-based) or structurally (i.e. multilayers) translatable to future work on silk ionomers. These projects all serve the purpose of advancing the understanding of materials and assembly strategies that will allow for the next generation of bioinspired responsive materials.
Design of multicomponent nanostructured surfaces with tailored optical properties

(Georgia Institute of Technology, 2017-07-05) Geldmeier, Jeffrey A.

Two promising ways of manipulating light-matter interactions at the nanoscale are through the use of noble metal plasmonic nanostructures and quantum dots. However, the majority of previous studies focus on single particle properties in solution instead of in mesoscale, organized, substrate-bound arrays and films. Understanding and guiding the assembly behavior of nanostructures in a large-scale, bottom-up, and controllable manner has important ramifications for controlling resultant unique properties for emerging optical applications. The primary goal of this research is therefore understanding, both experimentally and computationally, the principles that govern plasmonic and emissive properties of nanostructure assemblies that possess novel emergent optical properties. This work was focused into three concrete tasks for understanding, controlling, and tuning nanoscale optical properties through the use of nanoparticle coupling interactions, polymeric components, and large-scale assemblies: • Understanding the nanostructure assembly fundamentals that can result in broadband absorbing plasmonic nanostructure assemblies through controlled coupling and assembly behavior; • Gaining insight into the various morphologies of conjugated polymer and plasmonic nanostructure composites and how their combination can be utilized for reversible and stimuli-responsive plasmonic resonances; • Examining the morphology of quantum dot/polymer composite films and how their interfacial properties can be altered for the enhancement of quantum dot fluorescence using dewetting-induced far-field scattering. Overall, the integration of multiple components in nanoscale assemblies and the subsequent characterization processes presented in this work can be used to address several existing challenges in present photonic and sensor applications. The controlled combination and assembly of noble metal and semiconductor nanostructures realized during the course of this work can serve as future guides and frameworks for further control of light-matter interactions at the nanoscale.
Controlling light-matter interactions using local-assemblies and large-scale arrangements of plasmonic and quantum-confined nanostructures

(Georgia Institute of Technology, 2017-01-13) Malak, Sidney T.

The primary goal of this research is to develop an understanding of how the confinement mechanisms and resulting light-matter interactions of plasmonic and quantum dot nanostructures depend on three levels of system hierarchy. These levels of hierarchy include: individual nanostructures, their local-assemblies, and their large-scale arrangements. The surface confinement of plasmons and their plasmon resonances are focused on for plasmonic nanostructures. The quantum confinement of excitons and their radiative relaxation pathways are examined for quantum dots (QDs). By understanding the relationship between the nanostructure confinement mechanisms and the system hierarchy, light-matter interactions can be measured and controlled. In the proposed work, a variety of experimental deposition and patterning approaches are outlined that yield novel local-assemblies (stacked plasmonic nanostructures) and large-scale arrangements (hierarchical 3D plasmonic substrates and spatially modulated emission patterns). Physical, optical, and material characterization techniques are employed so that clear structure-property relationships can be established. These discoveries yield a general set of guidelines that can be referenced when designing and fabricating nanostructure-based photonic systems that need to exhibit specific optical characteristics. This scientific and engineering framework could accelerate the development of novel nanostructure photonic systems that exhibit properties like electric field enhancement, localized scattering/absorption, controlled optical amplification, and spatially modulated photoluminescence.
Atomic force microscopy probing methods for soft viscoelastic synthetic and biological materials and structures

(Georgia Institute of Technology, 2016-04-18) Young, Seth Lawton

The focus of this dissertation is on refining atomic force micrscopy (AFM) methods and data analysis routines to measure the viscoelastic mechanical properties of soft polymer and biological materials in relevant fluid environments and in vivo using a range of relevant temperatures, applied forces, and loading rates. These methods are directly applied here to a several interesting synthetic and biological materials. First, we probe poly(n-butyl methacrylate) (PnBMA), above, at and below its glass transition temperature in order to verify our experimental procedure. Next, we use AFM to study the viscoelastic properties of coating materials and additives of silicone-based soft contact lenses in a tear-like saline solution. Finally, a major focus in this dissertation is determining the fundamental mechanical properties that contribute to the excellent sensitivity of the strain sensing organs in a wandering spider (Cupiennius salei) by probing under in vivo conditions. These strain-sensing organs are known to have a significant viscoelastic component. Thus, the cuticle of living spiders is directly investigated in near-natural environments (high humidity, temperatures from 15-40 °C). The main achievements of these studies can be summarized through the following findings: We suggest that full time-temperature-modulus relationships are necessary for the understanding of soft materials systems, and present a practical method for obtaining such relationships. These studies will have a direct impact on both scientists in the metrology field by developing practical experimental procedures and data analysis routines to investigate viscoelastic mechanical properties at the nanoscale, and future materials scientists and engineers by showing via spider mechanosensory systems how viscoelasticity can be applied for functional use in sensing technology.