Browsing by Author "Li, Wei"

Now showing 1 - 20 of 41

An evaluation and redesign of a vision-based feedback controls experiment for undergraduate dynamic systems and controls laboratory
(2017-05) Campbell, Etse-Oghena Y.; Longoria, Raul G.; Li, Wei
Control systems instructional modules are more commonly developed for control systems engineering students, who are prepared to confront the complexity and large number of topics and concepts required in control systems study. In a general systems and dynamics course, it can be challenging to develop laboratory modules that will be suitable to, say, a general mechanical engineering student audience. This report describes and analyzes a pedagogical tool – a Vision-Based feedback control experiment – to investigate its effectiveness at demonstrating basic feedback control concepts to such a general purpose mechanical engineering undergraduate student audience. The effectiveness of this tool is examined by analyzing student responses to specific queries, designed to test understanding of a topic area or concept. This report evaluates the experimental apparatus pedagogical practice to give the instructor information required for an update on aforementioned practices, to better suit the target student audience, and to ultimately achieve desired module learning outcomes and objectives. The evaluation tools and methods are described in detail, and results show that the Vision-Based Feedback Control Experimental apparatus successfully demonstrates feedback control concepts to the desired student audience, and highlights areas where teaching practice may be improved to improve student comprehension of the concepts and topics presented in the module. The tools and methods presented in this report can be implemented for constantly monitoring the effect of changes and improvements, and are recommended for application to any of the other instructional lab modules in this type of course.
Automated drill bit forensics : enhancing efficiency and accuracy through image processing and machine learning
(2023-12) Chu, Jian, Ph. D.; Chen, Dongmei, Ph. D.; Oort, Eric van; Sha, Zhenghui; Ashok, Preadeepkumar; Li, Wei; Hasenbein, John
In recent years, the automation of drilling has garnered considerable attention within both the upstream oil and gas companies and the drilling research community. Drill bit forensics, being integral to the enhancement of efficiencies and profits in the oil and gas industries, promises heightened drilling efficiency, augmented consistency, and a refined comprehension of bit damage mechanisms through automation. Nevertheless, the adoption rate of drilling automation remains sluggish, largely due to the intricate nature of drilling operations. At present, the conventional inspection and grading of bit damage by human operators is labor-intensive and susceptible to human biases. This underscores the imperative for an automated system in drill bit forensics, which would aid drilling operators and specialists in processing and analyzing bit damage data. In this dissertation, a novel systematic framework is introduced, amalgamating computer vision and machine learning techniques with domain-specific knowledge of drill bits. This framework streamlines the evaluation process from identifying various drill bit components, quantifying and categorizing cutter damage, collating positional data, to ultimately forecasting the primary causes of damage. The methodologies devised are applied to visual data of drill bits, encompassing images and videos from hundreds of different bit runs. This work delves into several innovative contributions: (1) The industry's first bit detection model that segments distinct parts of the bit; (2) A pioneering proposition to utilize video data of drill bits to expedite the automation of bit forensics; (3) A comprehensive workflow tailored for diverse bit data sources; (4) An adaptable analytical methodology for discerning the root causes of bit damage. The outcomes underscore the potential of an automated system in drill bit forensics to bolster the precision and uniformity of drill bit assessments, offering invaluable insights into drilling operations. This groundbreaking methodology lays the foundation for further advancements in the realm of automated drill bit forensics, targeting the enhancement of the overall efficacy and cost-efficiency of drilling operations.
Automated estimation of time and cost for determining optimal machining plans
(2012-05) Van Blarigan, Benjamin; Campbell, Matthew I.; Li, Wei
The process of taking a solid model and producing a machined part requires the time and skillset of a range of professionals, and several hours of part review, process planning, and production. Much of this time is spent creating a methodical step-by-step process plan for creating the part from stock. The work presented here is part of a software package that performs automated process planning for a solid model. This software is capable of not only greatly decreasing the planning time for part production, but also give valuable feedback about the part to the designer, as a time and cost associated with manufacturing the part. In order to generate these parameters, we must simulate all aspects of creating the part. Presented here are models that replicate these aspects. For milling, an automatic tool selection method is presented. Given this tooling, another model uses specific information about the part to generate a tool path length. A machining simulation model calculates relevant parameters, and estimates a time for machining given the tool and tool path determined previously. This time value, along with the machining parameters, is used to estimate the wear to the tooling used in the process. Using the machining time and the tool wear a cost for the process can be determined. Other models capture the time of non-machining production times, and all times are combined with billing rates of machines and operators to present an overall cost for machining a feature on a part. If several such features are required to create the part, these models are applied to each feature, until a complete process plan has been created. Further post processing of the process plan is required. Using a list of available machines, this work considers creating the part on all machines, or any combination of these machines. Candidates for creating the part on specific machines are generated and filtered based on time and cost to keep only the best candidates. These candidates can be returned to the user, who can evaluate, and choose, one candidate. Results are presented for several example parts.
Bioinspired catecholic polymers for functional materials design
(2015-08) Cho, Joon Hee; Ellison, Christopher J.; Willson, Carlton Grant; Freeman, Benny D.; Li, Wei; Koo, Joseph H.
Melanins and Polydopamine (PDA) are bioinspired catecholic polymers that are well known for their intriguing chemical structure and physiological functions. Indeed, PDA has a suite of properties that are uncommon to many known organic materials and over the last decade researchers have endeavored to exploit those properties in technologically relevant materials. Those efforts notwithstanding, PDAs’ chemical structures have yet to be revealed in their entirety and their useful properties yet to be fully explored. In addition, given the natural presence of melanins and dopamine in many animals (including humans), along with their versatile functional features, these materials can serve as non-toxic additives to common polymers and thereby enhance their properties. Or they could, on their own, serve as eco-friendly functional organic films to be used in a variety of useful applications. To this end, we suggest first the potential of melanins as thermal stabilizers for common polymers by evaluating the addition of melanin to several model polymers with well-known degradation pathways. Small loadings of natural and synthetic melanins significantly alter the radical-initiated chain scission behavior of conventional polymers. Such loadings cause a dramatic increase in its onset decomposition temperature, indicating potential benefits for high temperature processing or increasing their upper use temperature in demanding applications. Second, we suggest thin films of synthetic melanin and poly(allylamine hydrochloride) be deposited layer-by-layer from dilute aqueous solutions in ambient conditions. The multilayer films show superior UV-protection performance and substantially extend the useful life of a conductive polymer film under UV light, demonstrating the utility of melanin films in high-tech applications. Third, we establish a synthetic approach to prepare block copolymers of poly(methyl methacrylate) (PMMA) and PDA using a modified atom transfer radical polymerization (ATRP) technique. These copolymers display very good solubility in a range of organic solvents and the spin cast thin films of the copolymers show a sharp reduction (by up to 50%) in protein adsorption compared to those of neat PMMA. The enhanced solvent processability, thermal stability, and low protein adsorption characteristics of this copolymer make it an attractive choice for antifouling coatings on large surfaces. Fourth, we exploit PDA to achieve block copolymer (BCP) lithography on a variety of soft-material surfaces. This biomimetic film serves as a reactive platform for subsequently grafting a surface neutral layer to chemically guide the perpendicular orientation of BCP lamellae. BCP nanopatterning may now be achieved over a large area on cheap, rough, and commercially available roll-to-roll flexible polymer substrates having a wide range of surface energies, surfaces that are of interest to be adapted for patterning. Fifth, we develop an efficient, environmentally friendly, and water-based flame-retardant surface nanocoating for highly flammable foamed materials such as flexible polyurethane (PU) foams. Upon exposure to flame, a PDA coating remains intact on the surface, completely stopping the melting and interrupting foam collapse. In addition, given the reported radical-scavenging capability of catechols, the PDA layer is hypothesized to remove flammable radicals which further retards flame spread during a fire. From cone calorimeter data, peak heat release rate of PDA-coated foams shows a sharp reduction, of up to 67%, relative to a control foam. This represents much better performance than many conventional additives for flexible PU foams that have been reported in the literature. We additionally investigated the effect of catechol functionality on the flammability of PU foams through the comparison of cone calorimetric analysis between PDA-coated flexible PU foams with pristine catechol functionality and LD-containing rigid PU foams with mostly depleted catechols. This new knowledge will be potentially useful in the design of flame-resistant foams and surface coatings.
Design and optimization of a long travel, two-axis flexural nanopositioning stage
(2024-05) Watts, Tyler Bennett ; Cullinan, Michael; Li, Wei
This thesis details the design, computational optimization, and resultant evaluation of a two-axis flexural nanopositioning stage based on a modified version of a double parallelogram flexure which features underconstraint-eliminating features nested within the flexural bearing. The stage was optimized using a response surface model with the seven most sensitive geometric parameters for the flexural bearing as inputs, and the flexure’s peak stress and reaction force at maximum deflection as outputs. This paper shows that—through design optimization—the first resonant mode of a long travel, two-axis flexural nanopositioning stage that has previously been reported in literature can be improved by a factor of two while still maintaining the higher-order resonant modes to be at least an order-of-magnitude higher than the fundamental mode of the stage. This improvement is critical because increasing the fundamental mode without sacrificing the higher order modes will allow for a higher bandwidth controller to be implemented on this nanopositioning stage. The end goal of the positioning stage detailed in this paper is to be implemented within a micro-SLS 3D printer.
Development of Pre-Repair Machining Strategies for Laser-Aided Metallic Component Remanufacturing
(University of Texas at Austin, 2018) Zhang, Xinchang; Cui, Wenyuan; Hill, Leon; Li, Wei; Liou, Frank
Remanufacturing worn metallic components can prolong the service life of parts that need frequent replacement but are extremely costly to manufacture, such as aircraft titanium components, casting dies. Additive manufacturing (AM) technology enables the repair of such valuable components by depositing filler materials at the worn area layer by layer to regenerate the missing geometry. In general, damaged parts would be inspected and pre-machined prior to material deposition to remove oil, residue, oxidized layers or defects located in inaccessible regions. Therefore, the motivation of this paper is to introduce pre-repair machining strategies for removing contaminated materials from damaged components and materials surrounding inaccessible defects to ensure that the target damage is repairable. The current research targets at common failures comprising surface indentations, erosion, corrosion, wear and cracking, and the machining strategies for each defect were proposed. Each strategy takes the 3D scanned damaged model as input and the cut-off volume around the defects is defined by using different approaches. Pre-repair machining toolpath and program were generated based on the defined cut-off volume and finally, damaged parts were machined using the proposed strategies.
Direct Laser Deposition of Ti-6Al-4V from Elemental Powder Blends
(University of Texas at Austin, 2015) Yan, Lei; Chen, Xueyang; Li, Wei; Liou, Frank; Newkirk, Joe
A thin-wall structure composed of Ti-6Al-4V has been deposited using direct laser deposition (DLD) from blended Ti, Al, and V elemental powders. The microstructure and composition distribution along the build height direction were intensively investigated using optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), and Vickers hardness testing. The microstructures of the as-deposited Ti-Al-V were studied using EDS to determine appropriate weight percentage for Al and V in the blended powders before mixing. The effects of laser power and laser transverse speed on the microstructure were investigated and optimized laser processing parameters were concluded.
Effect of Powder Particle Size on the Fabrication of Ti-6Al-4V using Direct Laser Metal Deposition from Elemental Powder Mixture
(University of Texas at Austin, 2016) Chen, Xueyang; Yan, Lei; Li, Wei; Liou, Frank; Newkirk, Joe
Direct Laser Metal Deposition (LMD) was used to fabricate thin-wall Ti-6Al-4V using the powder mixture of Ti-6 wt.%Al-4 wt.%V. Scanning electron microscopy (SEM), optical microscopy (OM) and energy dispersive spectroscopy (EDS) were employed to examine the chemical composition and microstructure of the as-deposited sections. Vickers hardness tests were then applied to characterize the mechanical properties of the deposit samples which were fabricated using pre-mixed elemental powders. The EDS line scans indicated that the chemical composition of the samples was homogenous across the deposit. X-ray diffraction (XRD) was used for the phase identification. After significant analysis, some differences were observed among two sets of deposit samples which varied in the particle size of the mixing Ti-6wt.%Al-4wt.%V powder. It could be found that the set with similar particle number for Ti, Al and V powder made composition much more stable and could easily get industry qualified Ti-6Al-4V components.
Energy-based periodic control of underactuated dissipative systems
(2021-05-07) Maweu, John Musembi; Longoria, Raul G.; Li, Wei
The variable length pendulum (VLP) is used as a platform to demonstrate that Lyapunov stabilizing control is achievable for underactuated systems in the presence of energy dissipation. The necessary background to describe the system is developed from elementary assumptions and Lagrangian mechanics. Phase portraits and limit cycles, whose discussion is essential to the development of the controller and to the presentation of results, are introduced. An existing Lyapunov control is adapted from the literature and extended to dissipative models and a discrete control. Nondimensionalization as described may be used for front-end engineering of model realizations. Results for control of both the VLP and the closely related skateboard model are then presented in a way that simplifies qualitative interpretations of the interactions of state variables.
Evaluation of transport and transport stability in glassy polymer membranes
(2014-05) Czenkusch, Katrina Marie; Paul, Donald R.; Freeman, B. D. (Benny D.); Sanchez, Isaac C; Ellison, Christopher J; Li, Wei
Both novel membrane materials with better separation characteristics and a better fundamental understanding of membrane transport stability are needed to improve the competitiveness of commercial membrane separations. In this work, the effect of a novel moiety, hexafluoroalcohol, on the gas transport properties of an aromatic polyimide membrane are evaluated. The hexafluoroalcohol group increases the membrane’s fractional free volume, which increases the membrane’s permeability to all gases. Additionally, the HFA-containing polyimide shows resistance to plasticization by carbon dioxide. However, ideal selectivity for several gas pairs is unchanged by the inclusion of hexafluoroalcohol and the increase in the polymer’s fractional free volume. This lack of selectivity loss with increasing free volume is attributed to hydrogen bonding between the hexafluoroalcohol and imide groups, which reduces chain mobility. The ethanol dehydration characteristics of a so-called “TR” polymer are also evaluated in this work. TR polymers are heterocyclic, aromatic polymers synthesized by a solid-state, high temperature condensation from ortho-functional polyimides. Pervaporation studies on a representative TR polymer film demonstrate that the material has separation properties that exceed those of a commercial ethanol dehydration membrane. The transport properties of the TR film, combined with high thermal and chemical stability characteristic of these materials, make TR polymers promising materials for high-temperature, high-water content ethanol dehydration. Finally, the physical aging and plasticization of cellulose triacetate, the dominant natural gas purification membrane, is presented. Although this material has been used industrially for over 30 years, the physical aging and plasticization of the material, particularly in sub-micron films, has never been studied. Although cellulose triacetate does show physical aging behavior, as observed by permeability decreases over time, cellulose triacetate thin films do not show accelerated aging. Furthermore, the plasticization of thin cellulose triacetate films is reduced, rather than increased as seen in other polymers. The unusual transport stability of thin cellulose triacetate films may be due to their complex, semi-crystalline morphology, which, due to the thermal instability of the material, may not be thermally controlled.
Experimental Characterization of a Direct Metal Deposited Cobalt-Based Alloy on Tool Steel for Component Repair
(University of Texas at Austin, 2018) Zhang, Xinchang; Pan, Tan; Li, Wei; Liou, Frank
Die casting dies made of tool steel is subject to impact, abrasion and cyclic thermo-mechanical loading that delivers damage such as wear, corrosion, and cracking. To repair such defects, materials enveloping the damage need to be machined and refilled. In this study, V-shape defects with varied sidewall inclination angles were prepared on H13 tool steel substrates and refilled with cobalt-based alloy using direct metal deposition (DMD) for superior hardness and wear resistance. The microstructure of rebuild samples was characterized using an optical microscope (OM) and scanning electron microscope (SEM). Elemental distribution from the substrate to deposits was analyzed using energy dispersive spectrometry (EDS). Mechanical properties of repaired samples were evaluated by tensile test and microhardness measurement. Fracture mechanism in tensile testing was analyzed by observing the fracture surface. The experiment reveals that V-shape defects with sidewall beyond certain angles can be successfully remanufactured. The deposits were fully dense and free of defects. The microstructure and tensile test confirm the solid bonding along the interface. The tensile test shows the mean ultimate tensile strength (UTS) of repaired samples is approximated 620 MPa, where samples fractured at the deposits region. Hardness measurement reveals the hardness of deposits is around 810 HV which is much higher than that of the substrate.
EXPLORATORY STUDY OF IN-SPACE WIRE ARC ADDITIVE MANUFACTURING WITH MODELING APPROACH
(University of Texas at Austin, 2023) Li, Wei; Bouzolin, Dan; Nagaraja, Kishore Mysore
Countries all over the world are rushing into space exploration due to crisis of energy and resources exhaustion on the Earth. Mars is an obvious target because it has a thin atmosphere, good geological similarity, and is close by in the Solar system. As the satellite of the Earth, Moon is another target since it is very close to the Earth. For the large spacecrafts such as Mars rovers, periodic maintenance is necessary to ensure the completion of long-duration exploration missions. In-space wire arc additive manufacturing (WAAM) provides a potential solution towards sustainable maintenance with onsite repair or additive manufacturing. For in-space manufacturing, reduced gravity is an important factor. In this work, WAAM processes under reduced gravity conditions on the Mars and Moon were studied through a multi-physics modeling approach. The metal droplet transfer, deposition geometry, thermal dissipation, and other key physics in WAAM were simulated. To validate the modeling approach, an experimental case was conducted on an in-house WAAM platform under the Earth condition.
Fabrication of collagen-based microfluidic devices for in vitro study of tumor microenvironment
(2016-12) Michna, Rhys James; Rylander, Marissa Nichole, 1978-; Li, Wei
Microfluidic technology has led to the development of advanced in vitro tumor platforms that overcome the challenges of in vivo animal and in vitro two dimensional models. This paper presents platform designs and methods used to develop in vitro models that replicate the tumor microenvironment. Features of these platforms include a continuous endothelium that allows for cell-cell interactions between vasculature and tumor cells. Additionally, we can recreate the abnormal shear stresses and the tortuous vasculature seen in patient tumors. Various methods such as subtractive, additive, and soft lithography techniques have been used by groups to manufacture complex microfluidic tumor models. A novel platform for fabrication of a single endothelialized microchannel encased within a collagen hydrogel hosting breast cancer cells was developed and utilized to study the influence of cellular interaction on transport phenomenon through vasculature in a hyperpermeable tumor microenvironment. We have confirmed the platforms ability to recapitulate physiological features of the tumor microenvironment and demonstrated the influence of tumor endothelial interactions on transport. Additionally, a second platform capable of combining lithographic techniques with additive tissue engineering methods was used to create endothelialized microfluidic networks that capture the more complex geometries of tumor microvasculature. By modeling microvascular networks after in vivo tumors we are able to create patient specific in vitro platforms that can be used to develop personalized patient treatments.
Fabrication of silicon nanowires with controlled nano-scale shapes using wet anisotropic etching
(2015-08) Yin, Bailey Anderson; Sreenivasan, S. V.; Banerjee, Sanjay K; Bonnecaze, Roger T; Cullinan, Michael A; Li, Wei
Silicon nanowires can enable important applications in energy and healthcare such as biochemical sensors, thermoelectric devices, and ultra-capacitors. In the energy sector, for example, as the need for more efficient energy storage continues to grow for enabling applications such as electric vehicles, high energy storage density capacitors are being explored as a potential replacement to traditional batteries that lack fast charge/discharge rates as well as have shorter life cycles. Silicon nanowire based ultra-capacitors offer increased energy storage density by increasing the surface area per unit projected area of the electrode, thereby allowing more surface “charge” to reside. The motivation behind this dissertation is the study of low-cost techniques for fabrication of high aspect ratio silicon nanowires with controlled geometry with an exemplar application in ultra-capacitors. Controlled transfer of high aspect ratio, nano-scale features into functional device layers requires anisotropic etch techniques. Dry reactive ion etch techniques are commonly used since most solution-based wet etch processes lack anisotropic pattern transfer capability. However, in silicon, anisotropic wet etch processes are available for the fabrication of nano-scale features, but have some constraints in the range of geometry of patterns that they can address. While this lack of geometric and material versatility precludes the use of these processes in applications like integrated circuits, they can be potentially realized for fabricating nanoscale pillars. This dissertation explores the geometric limitations of such inexpensive wet anisotropic etching processes and develops additional methods and geometries for fabrication of controlled nano-scale, high aspect ratio features. Jet and Flash Imprint Lithography (J-FIL™) has been used as the preferred pre-etch patterning process as it enables patterning of sub-50 nm high density features with versatile geometries over large areas. Exemplary anisotropic wet etch processes studied include Crystalline Orientation Dependent Etch (CODE) using potassium hydroxide (KOH) etching of silicon and Metal Assisted Chemical Etching (MACE) using gold as a catalyst to etch silicon. Experiments with CODE indicate that the geometric limitations of the etch process prevent the fabrication of high aspect ratio nanowires without adding a prohibitive number of steps to protect the pillar geometry. On the other hand, MACE offers a relatively simple process for fabricating high aspect ratio pillars with unique cross sections, and has thus been pursued to fabricate fully functional electrostatic capacitors featuring both circular and diamond-shaped nano-pillar electrodes. The capacitance of the diamond-shaped nano-pillar capacitor has been shown to be ~77.9% larger than that of the circular cross section due to the increase in surface area per unit projected area. This increase in capacitance approximately matches the increase calculated using analytical models. Thus, this dissertation provides a framework for the ability to create unique sharp cornered nanowires that can be explored further for a wider variety of cross sections.
The Failure of Wire-Arc Additive Manufactured Aluminum Alloys with Porosities under Loadings as Observed by In-situ X-Ray Micro-Computed Tomography
(2022) Zhang, Runyu; Jiao, Yuxin; Paniagua, Christopher; Tian, Yi; Lu, Hongbing; Li, Wei
Wire-arc additive manufactured aluminum alloys (WAAM 4043 Aluminum) are widely used in many industries. Porosities are known to exist within the WAAM aluminum alloys, which greatly reduces the usability and reliability of such parts. In this study, WAAM aluminum alloy samples with porosities are manufactured using a Fronius (TPS 320i) MIG/MAG welding and ABB (IRB 140) robot system. The porosities generated inside the samples and the porosity evolution under the uniaxial tension are observed using in-situ X-ray micro-computed tomography (μCT). The μCT system with an integrated mechanical loading frame provides in-situ volumetric images of the specimens while loadings are applied. The porosity evolution of the WAAM aluminum samples and the propagation of the internal pores are assessed. This work provides direct experimental observations and evaluations of the influence of porosities on the mechanical behavior of WAAM aluminum alloys under loadings.
Flame retardant nylon 6 nanocomposite fibers : processing and characterization
(2016-08) Wu, Hao, Doctorate in materials science and engineering; Krifa, Mourad; Koo, Joseph H.; Li, Wei; Ellison, Christopher J; Chen, Jonathan Y
One type of engineering thermoplastic polymers that has significant commercial application is nylon. However, flammability and melt dripping is a major problem for polymers like nylon 6 because it can cause fire to spread to other flammable objects and escalate the fire in a short amount of time. Although high performance inherently flame-retardant (FR) fibers have been discovered and various durable FR finishes for nylon have been developed, cost-effective flame retardant nylon and nylon blend fabrics remain a challenge. The goal of this research is to develop non-drip inherently FR nylon 6 fibers as a cost-effective alternative for use in high volume FR fabrics. In this dissertation, a cost effective alternative of producing non-drip inherently flame retardant nylon 6 fibers with balanced performances was developed based on polymer nanocomposite systems incorporating intumescent FR and nanoclay additives. Nanoclay was added to the system to reduce FR particle loading and capitalize on the synergistic effect between nanoclay and intumescent additives. Adequate dispersion of the additives with exfoliation of the nanoclay platelets was observed using TEM and XRD. Injection molding was used as a tool for screening the performance of the nanocomposite formulations in bulk form before the fiber spinning process. Results of injection molded FR PA6 nanocomposites suggest that although a good FR performance could be achieved, mechanical properties, especially ductility, were significantly compromised. To solve this problem, rubber toughening was achieved using a thermoplastic elastomer with significant success in recovering material ductility without compromising FR performance. Ultra-sonication of the FR additives prior the fiber spinning could effectively reduce the FR particle size distribution. Single fiber tensile tests show that PA6/FR/elastomer/nanoclay formulation is able to improve both the tenacity and elongation at break from the original PA6/FR system. Moreover, flammability tests suggest that the nanocomposite FR fibers have significantly lower heat release properties and are able to retain a fibrous shape after combustion indicating the non-dripping property. Therefore, our experiments have yielded improved non-drip FR properties in PA6 through the infusion of nanoclay and non-halogenated intumescent particles (FR) via co-rotating twin-screw extrusion. One major implication of these results is that with the new non-drip FR nylon 6 fiber, it would be possible to achieve blends with higher nylon content than customary and not compromise the FR performance of the fabric, thus providing a cost effective solution for high-volume applications.
Flexible all-gel-based supercapacitors
(2016-05-05) Al-Sudani, Atheer Kareem Qasim; Yu, Guihua (Assistant professor); Li, Wei
Flexible energy storage devices are important sources of power for flexible electronics such as role up screens and wearable electronics. Most of the flexible energy storage devices are based on using either carbon nanomaterials or using composite electrodes (carbon nanomaterials with conductive polymers). The main drawbacks of these approaches are: the cost, fabrication time consuming and difficulty of synthesizing proper carbon nanomaterials. An alternative promising approach is using the 3D nanostructured conductive polymer hydrogel, which exhibits good electrochemical performance and good mechanical properties. 3D nanostructured hydrogel has a porous nanostructured network, which has many advantages such as providing short pathways for electron transport and increasing the electrode-electrolyte penetration depth via pores. In addition, the porous structure can contribute to release chain’s strains due to the volume change during the charge-discharge processes. For energy storage devices that work under periodically critical engineering stresses, these hydrogels may suffer from micro cracks, which lead to degraded electrochemical performance over time, so increasing the flexibility of 3D nanostructured hydrogel is very important for flexible energy storage devices. In this thesis, we propose a new idea of synthesizing hybrid gel electrodes that are composed of 3D nanostructured hydrogel and small percentages of nonconductive gel (PANI+PEO). The conductive hydrogel was contributed to provide good electrochemical performance, and the nonconductive gel was used as a plasticizer to increase the flexibility of the hybrid gel electrodes. Adding small percentage of the plasticizer polymer in a controllable manner has kept high electrochemical performance, and greatly enhanced the mechanical properties of the flexible gel electrodes. In order to approve our idea, we designed three gel supercapacitors based on the differences in the PEO content in the hybrid gel electrodes, and then we performed a wide comparison among them in terms of electrochemical performance and the mechanical behavior.
Functional polymer grafted nanoparticles synthesis, characterization and applications
(2016-09-02) Fei, Yunping; Ellison, Christopher J.; Paul, Donald R; Sanchez, Isaac C; Freeman, Benny D; Li, Wei
Incorporating nanoparticles and polymers into one composite material have opened new pathways for generating novel material structures and advancing the properties of conventional materials. The developments in the field of nanocomposites have been accelerated by the progress in fabrication of nanoparticles with designed shape and precise size control, surface modification techniques covering a variety of nano-scale materials including clay sheets, carbonaceous materials, metal oxide particles, etc., as well as new syntheses of polymers with targeted architecture and functionality. The control of interfacial interactions is the key to property enhancement of almost all nanocomposite materials. Grafting polymer chains directly onto the surface of nanoparticles is a relatively new approach for obtaining novel nanocomposite structures and it offers better control of grafting density and maximizes the interfacial interactions between nanoparticles and polymeric matrices. The first project in this thesis describes the preparation of nanocomposites via surface initiated polymerization of block copolymer chains directly from the surface of montmorillonite clay. A ‘graft-from’ synthesis protocol was developed for the preparation of the nanocomposites. Comprehensive material characterization was performed to understand the structure and properties of the nanocomposites. Crystallization behavior of the bulk material and optical properties of nanocomposite films were examined. The relationship between material synthesis, structure and properties is also discussed in these chapters. The second project involves grafting polyelectrolytes onto magnetic nanoparticles for the application of electromagnetic imaging in high temperature, high salinity gas and oil reservoir environments. The fabrication of magnetic nanoparticles is described with a focus on both size control and achieving colloidal stability. The synthesized nanoparticles were used as core materials for their outstanding magnetic properties. Subsequent surface functionalization and a ‘grafting-to’ method was developed to coat the nanoparticles with a surface layer of polyelectrolytes, which provides nanoparticles with excellent transport mobility for high temperature, high salinity aqueous flow conditions through porous rock and sediment.
Heterogeneous integration of graphene and Si CMOS for gas sensing applications
(2014-12) Mortazavi Zanjani, Seyedeh Maryam; Akinwande, Deji; Banerjee, Sanjay K.; Aziz, Adnan; Sun, Nan; Li, Wei
Detecting presence of gas molecules is of prominent importance for controlling chemical processes, safety systems, and industrial and medical applications. Despite enormous progress in this field over past few decades on developing and improving various types of gas sensors, sensors with higher sensitivity, selectivity, lower sensing limit, and lower cost that can perform at room temperature are highly sought-after. Discovery of graphene and its succeeding progress in nanotechnology has paved the way to design ultra-sensitive gas sensors that can detect individual gas molecules while operating at room temperature. Graphene is a promising candidate for gas sensing applications due to its unique transport properties, exceptionally high surface-to-volume ratio, and low electrical noise. In this dissertation, a graphene gas sensor fully integrated with silicon CMOS platform is presented, and its performance for detecting NO₂ and NH₃ gas molecules is investigated. This integration helps benefit the high gas sensitivity of graphene at room temperature as well as the compact size, robustness, low cost, and advantages of standard industrial scale production of CMOS technology. Recent progress in large scale growth of CVD graphene paves the path toward commercialization of graphene-based CMOS sensors to provide highly sensitive low-cost sensors for industrial applications. To best of our knowledge, this work is the first integration of mono-layer graphene and silicon CMOS. Also, this is the first implementation of graphene integrated gas sensor. Heterogeneous integration of monolayer graphene and silicon CMOS can introduce a platform to exploit the unique electronic properties of monolayer graphene for gas sensing applications and also take a step further toward commercialization of ultrasensitive monolithic graphene-based gas sensors. Furthermore, we were able to enhance sensitivity of CVD graphene to NH₃ by almost an order of magnitude. We experimentally showed that sensitivity of graphene to NH₃ can be enhanced by 7 folds compared to as-fabricated graphene by introducing NO₂ molecules as dopants. We observed this enhancement for graphene sensors microfabricated on SiO₂/Si substrate, as well as our integrated graphene-CMOS sensors. This finding not only increases current understanding on adsorption mechanisms of molecules to graphene, but also takes another step toward commercialization of graphene sensors.
Hybrid systems of plasmonic nanostructures and functional materials for light-matter interactions and active plasmonic devices
(2018-08-15) Wang, Mingsong; Zheng, Yuebing; Ben-Yakar, Adela; Milliron, Delia; Li, Wei
Advances in nanofabrication and characterization of nanomaterials enable the development of plasmonic nanostructures with unique optical properties. Plasmonic nanostructures have been extensively studied for their potential applications in optical sensing, photothermal therapy, photovoltaics, and photocatalysis. In this dissertation, we present studies of light-matter interactions in hybrid systems consisting of plasmonic nanostructures and functional materials. These studies are focused on four major types of light-matter interactions in plasmonic nanostructures: (1) plasmon-induced resonance energy transfer (PIRET); (2) plasmon-enhanced spontaneous emission; (3) Fano interference between plasmonic nanostructures and emitters; and (4) strong plasmon-exciton coupling. We also achieved the tuning of light-matter interactions by modifying the physical properties of functional materials or plasmonic nanostructures. In addition, the active control of light-matter interactions was demonstrated by integrating plasmonic nanostructures with switchable materials, such as photochromic dyes. Specifically, we first demonstrated the blue-shifted PIRET from a single gold nanorod (AuNR) to dye molecules. AuNRs enable the energy transfer from plasmonic donors to dye acceptors with light having a longer wavelength and lower intensity, compared to dye donors. Secondly, we studied the tuning of plasmon-trion and plasmon-exciton resonance energy transfer from a single gold nanotriangle (AuNT) to monolayer MoS₂. We achieved these phenomena by the combination of rationally designed monolayer MoS₂-plasmonic nanoparticle hybrid systems and single-nanoparticle measurements. Thirdly, we realized the large modulation of hybrid plasmonic waveguide mode (HPWM) in single hybrid molecule-plasmon nanostructures through the strong molecule-plasmon coupling. The HPWM features both the capacity of plasmonic nanostructures to manipulate light at the nanoscale and the low loss of dielectric waveguides. Fourthly, we demonstrated the photoswitchable plasmon-induced fluorescence enhancement. This large switchable modulation of fluorescence was derived from the large near-field enhancement at the subnanometer gap between Au nanoparticles and switchable intersystem crossing as a nonradiative decay channel in photochromic dyes. Finally, we achieved tunable Fano resonances and plasmon-exciton coupling in two-dimensional (2D) WS₂-AuNT hybrid structures at room temperature. The tuning of Fano resonances and plasmon-exciton coupling were achieved by the active control of the WS₂ exciton binding energy and dipole-dipole interaction through controlling the dielectric constant of the surrounding medium.