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School of Materials Science and Engineering

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College of Engineering

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Now showing 1 - 10 of 32

Chirality control of tailored one-dimensional polysaccharide nanocrystals

(Georgia Institute of Technology, 2024-04-27) Bukharina, Daria

One-dimensional polysaccharide nanocrystals, derived from living organisms, can self-organize into complex structures that possess long-range hierarchical order making them great candidates for high-performance structural composites with multifunctional capabilities. Their abundance in nature and biodegradability makes them excellent candidates as sustainable materials of the future. However, a greater fundamental understanding of how these nanoscale building blocks organize into functional microstructures is needed to push the boundaries of mechanical and photonic metamaterials for the future. The goal of this thesis is to uncover the intrinsic mechanisms behind self-assembly phenomenon in natural systems, understand the critical forces and parameters required for their successful hierarchical organization into chiral nematic structure and with those insights manipulate the surface chemistry to create self-assembly templates for use in photonic films for optical filters, chiral encryption, smart coatings, or biosensors. In this thesis, we first provide fundamental insight into how chiral interactions in 1D polysaccharide systems emerge, using cellulose nanocrystals (CNCs) as an example. Then, we show how CNCs interactions can be tuned and controlled via their surface modification. By functionalizing them with single stranded DNAs we show the possibility for CNCs chiral complexation through DNA-guided assembly. A nanoscale-controlled strategy to induce stimuli responsiveness and dynamic chirality. The challenges of this process and strategies to overcome them are discussed. Lastly, a top-down 3D printing approach to engineer chiral CNC-based photonic crystals with unique optical activities is developed here. This method shows how thin films capable of controlled pre-programmed circularly polarized absorbance and emission can be constructed from CNC-composites for future smart coatings, optical encryption, or optical filters. Overall, the goal of this work is to inspire applicational implementation of bioderived nanocrystals by demonstrating how their properties can be controlled and tailored based on the application. This work advances fundamental understanding of the assembly of polysaccharides nanocrystals in nature and creates a toolset to aid in the design and engineering of future metamaterials.
Polymer-Ligated Nanocrystals with Tunable Dimensions, Compositions, and Architectures

(Georgia Institute of Technology, 2022-11-01) Zhang, Mingyue

The ability to produce monodisperse nanocrystals with stable and tunable surface chemistry is of key importance to render investigation into their size- and shape-dependent physical properties and thus an array of applications including electronics, photonics, catalysis, sensors, energy storage, information technology, bionanotechnology, etc. In this context, nonlinear block copolymer nanoreactor has emerged as a general and robust route to synthesis of a gallery of nanocrystals with precisely controlled sizes, shapes, compositions, and surface chemistry. In this thesis, I capitalized on a set of rationally designed star-like and bottlebrush-like block copolymer to template the growth of a host of functional 0D and 1D nanocrystals with controlled dimensions, compositions, and architectures, and scrutinize the dependence of physical properties and energy-related applications on their size, shape, and surface chemistry. First, a series of star-like copolymers were synthesized via sequential atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA) and styrene from star-like macroinitiators, brominated β-cyclodextrin (β-CD). Due to the living nature of ATRP, the molecular weight of each polymer block can be precisely controlled by simply tuning polymerization time and a low polydispersity index (PDI) can be achieved. The inner hydrophobic poly(tert-butyl acrylate) (PtBA) blocks were then converted into hydrophilic poly(acrylic acid) (PAA), which strongly coordinates with the metal moieties of precursors of targeted nanocrystals, leading to the nucleation and growth of nanocrystals confined within the space occupied by the PAA blocks. As a result, the size and shape of nanocrystals can be readily controlled by the molecular weight of PAA blocks (i.e., diameter of nanoparticles). Moreover, the outer PS blocks, originally covalently linked to the inner PAA blocks, form a layer of permanently anchored ligands on the nanocrystal surface to enable stable surface chemistry. This synthetic strategy were successfully applied for preparing a diversity of functional nanoparticles for the investigation into their physical properties and applications. Specifically, this judiciously designed nanoreactor was utilized to craft monodispersed magnetic spinel CoFe2O4 nanoparticles, which was studied for their magnetic and surface chemistry related electrocatalytic activity. It was the first systematic scrutiny of the influence of spin-pinning effect in spinel nanoparticles realized via surface reconstruction on the oxygen evolution reaction (OER). Second, using the same chemistry, 1D bottlebrush-like PAA-b-PS templates can be realized by employing brominated cellulose (Cell-Br) as macroinitiators. Due to the larger number of side chains on one Cell-Br macroinitiator (ranging from about 40 chains to more than 150 chains), high quality bottlebrush-like block copolymers are more challenging to synthesize than star-like block copolymers, which only have 21 arms. Systematic scrutiny was made to investigate the reaction conditions (e.g., catalyst ratio, ligand ratio, reaction concentration, degassing method, etc.) that affect the uniform growth of the highly dense block copolymer side chains, which has a determining effect on the quality of the bottlebrush-like templates and their application as nanoreactors for the synthesis of 1D nanocrystals. In addition to focusing on the precise synthesis of 0D and 1D nanocrystals via nanoreactor strategy, this thesis also covers the practical application of multi-functional nanocomposites. In this work, a ternary nanocomposite consisting of antibacterial silver (Ag) NPs, photocatalytic titania oxide (TiO2) NPs, and upconverting NPs are prepared, manifesting a greatly enhanced biocidal performance under ambient environment. It was found that the visible light (blue) and ultraviolet (UV) light which were converted from near infrared (NIR) radiation by the NaYF4@Yb:Tm upconverting NPs can be effectively absorbed by Ag and TiO¬2 NPs to generate electrons and electron-hole pairs, respectively. Reactive oxygen species (ROS) could then be produced from the reactions between environment and the electrons and holes to terminate bacteria. The outstanding antibacterial performance of this nanocomposite system renders it the potential to be used in food packaging industry. Moreover, reversible photo responsive Ruddlesden-Popper 2D perovskite nanoplatelets were explored in this thesis. Colloidal two-dimensional RP perovskite nanoplatelets with a general formula L2(ABX3)n-1BX4 are a rapidly emerging type of semiconductor materials with excellent optical and electronic properties. Research on the functional organic spacers (L) has become a popular direction in the past several years. Inspired by our previous research about reversible photo-crosslinkable nanoparticles realized by capitalizing on star-like nanoreactors with photo responsive coumarin containing repeat units in the outer block, the preparation of RP lead halide perovskite nanoplatelets with coumarin containing ammonium as organic spacers was attempted. Molecular modification and mixed organic spacer strategies were adopted to overcome the solubility limitation of coumarin containing molecules in non-polar solvents. Such coumarin containing 2D perovskite nanoplatelets will undergo controllable and reversible layer-by-layer crosslinking and de-crosslinking under radiation of certain wavelength, leading to many intriguing and tunable optical and electronic properties.
Nanoscale Characterization of Hierarchical, Natural and Synthetic Low-Dimensional Composites

(Georgia Institute of Technology, 2022-08-01) Adstedt, Katarina M.

Low-dimensional nanocomposites are promising material composites for use as high-performance materials due to their unique strength-to-weight ratios and multifunctional properties. Their application fields are diverse, acting as structural materials in lightweight electronics, defense systems, or health care devices, or as biosensors and energy storage devices. However, these low-dimensional nanocomposites have yet to reach their ultimate performance due to a gap in fundamental understanding of nanofiller intercalation mechanisms and the ultimate role of chemistry-structure-property relationships. This work will focus on the chemical and structural changes in nanocomposite systems with the introduction of nanofillers, revealing the intercalation mechanisms and role of chemistry and structure in influencing the final properties. The first task aims to understand how nanofiller content intercalates with one-dimensional cellulose nanocrystals to create an entirely natural, bio-based nanocomposite, and reveal the critical limit to nanofiller integration and correlating the resulting structural and chemistry changes to the optical and mechanical performance. The second task aims to uncover what unique structural formations exist on carbon fiber surfaces, revealing how nanostructures increase mechanical performance in synthetic composites. Finally, the third task unveils how two-dimensional architecture and chemistry, for graphene oxide and MXene nanoflakes, alters the mechanical, electrostatic, chemical, and morphological properties of synthetic nanocomposites. This work will inspire the optimal design of low-dimensional nanocomposites, demonstrating how to achieve enhanced mechanics while sustaining or enhancing the optical or conducting properties. These studies provide a framework for understanding the intercalation and absorbing mechanisms of nanocomposites and which aspects can be tailored for ultimate property control.
Capillary and Localized Magnetic Effects in Cellulose Nanocrystal Thin Films

(Georgia Institute of Technology, 2022-04-27) Pierce, Kellina

Bioderived materials such as cellulose nanocrystals (CNCs) have inherent structural organization that can be exploited for the control of dimensionality, periodicity, and functionality of biocompatible and photonic materials. However, precise control and tunability of organized cellulose nanocrystal-based materials is challenging due to the random organization of the chiral nematic structure, called tactoids, during evaporation induced self-assembly (EISA) of solid films. Lack of fundamental assessment of CNC-centric materials has limited applications for the sustainable, bioderived material since control over its fundamental behavior orients the entire understanding for the chiroptic potential of those materials. This work focuses on the control of lyotropic LC alignment of CNCs by (i) utilizing geometric confinement for asymmetric evaporation that induces directional flow of LC suspension, (ii) direct chemical modification of the surface groups for control of inter-particle interactions, and (iii) applying magnetic fields for localized CNC alignments and global patterned formation. Firstly, we utilized tunicate-inspired hydrogen-bonding-rich 3,4,5-trihydroxyphenethylamine hydrochloride (TOPA) for physical crosslinking of nanocrystals and polyethylene glycol (PEG) as a relaxer of internal stresses in the vicinity of the capillary surface. The CNC/TOPA/PEG film is organized as a left-handed chiral structure parallel to flat walls, and the inner volume of the films displayed transitional herringbone organization across the interfacial region. Secondly, we utilized polyethyleneimine (PEI) coated Fe3O4 magnetic nanoparticles to produce localized magnetic patterns in CNC thin films under weak magnetic fields. The resulting CNC films showed tailored optical patterns controlled by localized magnetic patterns while retaining a iridescent optical appearance. The significance of this work being that the tuning and control over the materials’ magnetic properties allows for a bottom-up approach towards a controlled assembly of larger scale materials with localized pattens. Overall, this work advances the dynamic control over CNC films to widen the range of applications available for multi-stimuli response, biocompatible films and gels of interest in biosensing and tunable optical reflectors.
BRANCHED POLYMER ELECTROLYTES: RESPONSIVE NANOMATERIALS FOR CONTROLLED ION MOBILITY

(Georgia Institute of Technology, 2021-05-01) Erwin, Andrew J.

Polymers containing ionic groups such as polyelectrolytes and polymerized ionic liquids are promising candidates for the design of organized ionically conductive media due to their controlled morphology, robust chemical and thermal stability, and single-ion conductivity. However, while polymerization of ionic groups affords electrolytes a greater degree of dimensional control, the effect of nonlinear chain architecture remains mostly an unexplored consideration, despite the unique functional group densities, chain conformations, counterion condensation, and dynamics of branched polymers. First, the stimuli-responsive interfacial assembly and tunable morphologies of star-shaped polyelectrolyte block-copolymers and polymerized ionic liquids in monolayers and multicomponent systems are examined. In the former case, a dual-responsive star-graft block-quarterpolymer with variable arm number, arm length, and grafting density are integrated into hydrogen-bonded multilayer films and their morphologies were evaluated in different environments using surface probe microscopy and neutron reflectivity. The results point toward the amphiphilicity endowed by the star-graft architecture as the chief factor controlling the temperature and pH-induced conformational changes which lead to the diverse star-like clustering at the molecular scale. Likewise, the surface organization of linear and star-shaped polymerized ionic liquids in monolayers and multilayers is compared under variable adsorption conditions for polymers with the different branching architectures. Both studies demonstrate how polyelectrolytes and polymerized ionic liquids with branched architecture assemble into multilayer films with variable porosity, thickness, and textured morphologies featuring compartmentalized internal morphologies that are remarkably distinct from traditional multilayer systems. The second part of this work focuses on the ion transport in polyelectrolytes comprised of star and hyperbranched polymerized ionic liquids. Long-chain arms were found to exhibit more sluggish and elastic dynamics at longer timescales while the glass transition temperature, rates of segmental relaxation, ion disassociation, and dc conductivity were similar regardless of the polymer architecture and arm length. But when polymerized ionic liquids are branched on a smaller scale, such as in the ionic liquid tethered macromolecules consisting of both POSS and hyperbranched polyester cores, considerable shifts in the glass transition temperatures and conductivities were observed. This ability to control the ion mobility in polymerized ionic liquids near the Tg is critical for the development of solid-state electrolytes in which it is desirable to have high conductivities in the near glassy state. Overall, this dissertation provides an initial view of branched polymer electrolytes as uniquely versatile nanomaterials in the assembly of multifunctional polymer electrolytes with tunable morphologies and controlled ion transport properties.
Interfacial Assembly of Natural and Synthetic Components for Functional Bionanocomposites

(Georgia Institute of Technology, 2021-05-01) Krecker, Michelle C.

Organized bionanocomposites are promising new materials since they are biocompatible, biodegradable, and can be used in a variety of applications such as flexible electronics, wearable sensors, and molecular sieving membranes. However, their mechanical and functional performance is not up to theoretical predictions due to a gap in understanding fundamental interactions between the biopolymeric and synthetic components of multilayered composite films. This work will focus on chemical and morphological changes of structural proteins in intimate contact with two-dimensional nanofillers when exposed to differing chemical environments and the resulting mechanical and conductive properties of multilayers composites. The first task aims to unveil the mechanisms behind silk fibroin’s natural morphological reorganization in direct contact with the surface of Ti3C2Tx MXene over time in aqueous solution. In the second task, the mechanical properties of silk-MXene multilayered composite films were investigated. Finally, suckerin-12 protein encapsulated MXene flakes are fabricated and their morphological reorganization in response to salt annealing was studied. These studies showed that MXene can be uniformly encapsulated by proteins with secondary structures that can be manipulated with non-covalent methods. Organized layered nanocomposites formed from these hybrid materials display enhanced mechanical properties dependent upon protein concentration and secondary structure. This work will inspire the fabrication of functional bionanocomposites with tailorable properties facilitated through interfacial interaction manipulation via non-covalent methods. These studies provide a framework for understanding interfacial interactions between structural proteins and two-dimensional synthetic materials and outlines techniques with which functional organized protein composites can be designed.
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.