FABRICATION, CHARACTERIZATION AND APPLICATIONS OF HIGHLY CONDUCTIVE WET-SPUN PEDOT:PSS FIBERS

Smart electronic textiles cross conventional uses to include functionalities such as light emission, health monitoring, climate control, sensing, storage and conversion of energy, etc. New fibers and yarns that are electrically conductive and mechanically robust are needed as fundamental building blocks for these next generation textiles. Conjugated polymers are promising candidates in the field of electronic textiles because they are made of earth-abundant, inexpensive elements, have good mechanical properties and flexibility, and can be processed using low-cost large-scale solution processing methods. Currently, the main method to fabricate electrically conductive fibers or yarns from conjugated polymers is the deposition of the conducting polymer onto an inert fiber support by using different techniques. However, the volume occupied by the electrically active coating is generally very small relative to the volume of insulating fiber acting as support. Therefore, when considering the total volume, the bulk electrical conductivity of these coated textiles is usually small, often lower than 10 S/cm, which limits their applications. An interesting alternate approach would be to fabricate fibers directly from the electrically conductive material avoiding the need for an inert-fiber support. Therefore, in this work, a wet-spinning process for the fabrication of PEDOT:PSS fibers with high electrical conductivity and robust mechanical properties is described. The process includes a coagulating step, a drawing step in a dimethyl sulfoxide bath and two drying steps. The effect that drawing the fibers in the DMSO bath has on the electrical, thermoelectric and mechanical properties of the fibers is studied and correlated to the changes observed in the fibers’ structure. In general, the fibers with the highest state of preferential orientation of crystal planes are also the most conductive and stiffest. In order to further improve the electrical properties of the fibers, substituting the DMSO drawing step by a sulfuric acid drawing step in the fabrication process is investigated. The sulfuric acid drawn fibers have higher electrical conductivities and better mechanical properties than the DMSO drawn fibers. In fact, electrical conductivities as high as 4039 S/cm and break stresses around 550 MPa are obtained which, to the best of our knowledge, are the highest reported for a PEDOT:PSS fiber. The mechanism by which sulfuric acid enhances the electrical and mechanical properties of the fibers is also investigated. It is found that the sulfuric acid treatment is very efficient removing PSS from the fibers while also promoting substitution of PSS by sulfates as counterions. The removal of PSS and substitution of counterions leads to a reorganization of the crystal structure of the fibers that is more favorable for charge transport. The last part of this work focuses on the application of the fibers. The mechanical properties of the fibers are compared to traditional textile fibers. Additionally, the time stability of the electrical conductivity of the fibers is also studied. Moreover, the maximum current carrying capacity or ampacity of the fibers is investigated together with some Joule heating-based applications such as thermochromic textiles. A thermoelectric textile device is also demonstrated using the fibers as the p-type legs. Finally, electrochemical applications of the fibers are discussed and demonstrated

A cooling system for s.m.a. (shape memory alloy)based on the use of peltier cells

The aim of this thesis has been the study and the implementation of an innovative cooling system for S.M.A. (Shape Memory Alloy) material by using a Peltier cell. This system has demonstrated a consistent cooling time reduction during the application and so that the solution adopted has confirmed that it can be used for a better operability of the S.M.A. material during the cooling phase. After an accurate selection of possible cooling system to be adopted on these materials the better choice in terms of efficiency and energy consumption reduction has converged on Peltier cell design development. In this context for our research three investigation have been conducted. The first one has concerned an analytic investigation in order to understand the phenomenology and the terms involved during the heat exchange. After this study a numerical investigation through a Finite Element approach by commercial software has been carried out. Also an experimental investigation has been conducted, at the CIRA Smart Structure Laboratory, in order to verify the results obtained by the numerical prediction. The set-up with the Peltier cell used as heater and cooler of the S.M.A. has confirmed the soundness of the solution adopted. Finally, a correlation between numerical and experimental results have been presented demonstrating the validity of the obtained results through the developed investigations. This system, composed of Peltier cell has confirmed also an energy consumption reduction because the cell has been used for heating and cooling phase without additional system as resistive system (Joule effect). This project shall be also industrial involvement in a new cost cut down point of vie

Tailored carbon based nanostructures as components of flexible thermoelectric and other devices

Carbon based nanostructures, such as fullerenes, carbon nanotubes and graphene showed a high potential for a vast of electronic and energy applications. However, properties of such materials in pristine forms can be insufficient to satisfy diverse specific demands, and tailoring their intrinsic properties is of increasing importance. In this work, different types of single-walled carbon nanotubes (SWCNTs) with controlled semiconducting fractions are p-/n-type doped by chemical doping in an attempt to tailor physical properties of the SWCNTs for the use in flexible thermoelectric (TE) devices and thermoplastic polymer-based conducting composites. Several p-/n-type doping schemes and an electronic type separation strategy have been developed to fulfill the task. A complete solution for efficient and scalable production of doped SWCNTs for the fabrication of flexible thermoelectric components is developed in this work. For p-type doping, a combined experimental and theoretical work demonstrates that boron atomic doping is an efficient way to simultaneously improve Seebeck coefficient (S) and electrical conductivity (σ) of SWCNT films, showing an increased thermoelectric power factor (S2σ) up to 255 μW/mK2 by a factor of 2.5 comparing to the pristine SWCNTs. For n-type doping, treatment of SWCNTs with potassium oxide and crown ether solution lead to a negative Seebeck coefficient of -30 μV/K and a promising S2σ up to 50 μW/mK2. A gel chromatography method has been developed to separate large-diameter (1.2-1.8nm) SWCNTs by electronic properties and to increase the purity of the sorted semiconducting carbon nanotubes (sc-SWCNTs) up to 95%. Effects of p-/n-type doping induced by different plasma treatments on the thermoelectric properties have been investigated for thin films made of sorted sc-SWCNTs. The high-purity sc-SWCNTs show significantly improved S of 125 μV/K. As the effects of p-type doping, air plasma treatments with proper duration (40s) lead to the increase of S, σ and thus S2σ up to 190 μW/mK2. The n-type doping for the SWCNT films have been performed via ammonia plasma treatment, and a negative S value of -80 μV/K has been achieved in air at 110oC, which is one of the best values ever reported for n-type carbon nanotube films. A flexible thermoelectric module was fabricated by printing ink made of the prepared boron doped SWCNTs and an organic solvent as an example for producing efficient all-carbon thermoelectric generators. At a temperature difference ΔT=60 K, the output voltage reaches 20 mV and the power output of 400 nW is obtained, although no “n”-legs are used in this module. At last, a work has been done on the development of melt mixed composites as TE materials, in which polypropylene is used as the matrix and boron-doped SWCNTs are used as conducting fillers. A percolation threshold lower than 0.25wt. % and a maximum conductivity up to 125 S/m at 5wt. % of SWCNT load have been achieved. The maximum conductivity is more than two times higher than that of the composites made with pristine SWCNTs as fillers

Synthesis of Organo-metallic Coordination Polymers for Thermoelectric Application

As an intriguing class of thermoelectric (TE) candidates, organometallic coordination polymers (OMCPs) have become a new research focus in this area, regardless of the extensive research on inorganic and organic thermoelectric materials. This thesis showcases the synthesis and comprehensive characterization of a series of linear OMCPs based on metal-bis(dithiolato) coordination, Ni-ett, Ni-diett and Ni-btt (Chapter 2). The studies proved that changing organic ligands is a successful strategy to tune the thermoelectric properties of OMCPs, including electrical conductivity, Seebeck coefficient and power factor. By developing complex model for analogous spectroscopic study, we proved the polymer frames of three OMCPs are radial involving. Moreover, alternative synthetic route was also developed for polymer Ni-btt. Meanwhile, a couple of structural isomeric ligands OMCPs (Chapter 3), benzene-1,2,3,4-tetrakis(thiolate) and benzene-1,2,4,5-tetrakis(thiolate), were employed to synthesize mono-ligand OMCPs (Ni-ibtt and Ni-btt) and dual-ligand OMCPs Ni(ibtt)x(btt)1-x. The comparative study upon their thermoelectric properties was correlated with their structural difference in both intrachain and interchain characters. Regardless of organic bridging ligand, the metal center is the other most important role on the thermoelectric properties of OMCPs. Systematic comparison among OMCPs with different metal centers cross reports is usually unfeasible, as chemical composition and properties for a certain OMCP formula usually (like Ni-ett) differ from ii report to report and involve multiple reaction and measurement factors. In this study, OMCPs with various metal cations were synthesized in the M-ett and M-btt system to conduct a parallel comparison in their thermoelectric performance (Chapter 4). Preliminary molecular design and synthesis work were also carried out to experimentally obtain the OMCPs based on benzenetetrathiolate backbone with different sidechains, to examine the effect of sidechains on thermoelectric properties in this system

Nano-estructuras tridimensionales funcionales (alúmina 3D y redes de nanohilos interconectados en las 3 direcciones del espacio)

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 09-03-2022This Thesis has been focused on the development of functional nanostructures for a variety of applications, from structural coloring to magnetic nanostructures with tailored properties and highly efficient thermoelectric metamaterials. In all cases, the fabrication of such nanostructures has been based on two processes: aluminum anodization and electrochemical growth. Both are chemical processes, which need no vacuum and that are well known at the industrial level. The results that are presented in this manuscript represent the state of the art of both techniques, which is well endorsed by the publications that have resulted from it.In brief, the main objective pursued in this Ph.D. Thesis has been to prove the versatility of a recent kind of alumina membranes, consisting of longitudinal pores that are transversely perforated by smaller pore channels, in the development of future nanotechnology applications. These 3D-Anodic alumina templates (3D AAO) have been studied by themselves, but also used as templates to grow different materials and tune their properties...Este trabajo de tesis se centra en el desarrollo de nanoestructuras funcionales interconectadas para diversas aplicaciones, desde la obtención de color estructural a la fabricación de metamateriales magnéticos con propiedades modificadas, así como metamateriales termoeléctricos de alta eficiencia. En todos estos casos, la fabricación de estas nanoestructuras se ha basado en dos procesos: anodización de aluminio y crecimiento electroquímico. Ambos son procesos químicos que no requieren de vacío y que son muy conocidos a nivel industrial. Los resultados que se presentan en este manuscrito muestran el estado del arte en ambas técnicas, lo que queda patente por las publicaciones científicas a las que este trabajo ha dado lugar. Brevemente, el objetivo principal de esta Tesis ha sido probar la versatilidad de un tipo de membranas de alúmina desarrolladas recientemente para el desarrollo de futuras aplicaciones nanotecnológicas. Estas membranas consisten en poros longitudinales que están unidos por poros transversales más pequeños que forman canales que los conectan. Estas membranas de alúmina tridimensionales (3D-AAO, del inglés 3D Anodic Aluminum Oxide) se han estudiado, por un lado, como plataformas para la generación de dispositivos en sí mismas, y, por otro lado, como plantillas para crecer en su estructura porosa distintos materiales y nanoestructurarlos, modificando de este modo sus propiedades...Fac. de Ciencias FísicasTRUEunpu

Aerosol-Jet Printed Nanocomposites for Flexible and Stretchable Thermoelectric Generators

Converting waste heat from the environment into usable electricity, via thermoelectric generators (TEGs) based on thermoelectric (TE) materials, is predicted to be one of the most promising renewable energy solutions of the future. TE materials produce a current when subjected to a temperature gradient as a result of the Seebeck effect, and are characterised by a TE figure of merit, ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the operating temperature, and κ is the thermal conductivity. TEGs can be used as an energy source for ‘small-power’ applications, such as wireless sensors and wearable devices. Nonetheless, traditional inorganic TE materials pose significant challenges owing to their high cost, toxicity, scarcity, and brittleness, particularly when it comes to applications requiring flexibility and/or stretchability. On the other hand, organic TE polymers are less expensive, environmentally friendly, and flexible. However, they typically suffer from poor TE performance due to their comparatively low S and σ. This thesis therefore seeks to explore solutions for high-performance and mechanically conformable TEGs based on organic-inorganic TE nanocomposites, adopting a material engineering approach to enhancing TE properties while ensuring the flexibility and/or stretchability of TEGs. In this work, a flexible and robust TEG based on a novel hybrid nanocomposite structure for harvesting energy from low-grade waste heat, has been successfully fabricated via a customised and scalable aerosol-jet printing (AJP) technique. Firstly, Bi2Te3 nanoparticles and Sb2Te3 nanoflakes were fabricated using a solvothermal synthesis approach, and their resulting morphological and microstructural properties were studied. They were then incorporated into a conducting polymer matrix poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) via the AJP method, resulting in well-dispersed TE nanocomposites on flexible polyimide substrates. These TE nanocomposites comprised Bi2Te3/Sb2Te3 nano-inclusions with higher S and σ embedded within a polymeric PEDOT:PSS matrix having lower κ. The compositions were dynamically tuned and controlled by the in-house developed in situ mixing method to optimise the resulting power factor (PF = S2σ). The AJP technique used in this work allows functional materials to be printed from inks with a wide range of viscosities and constituent particle sizes and shapes. The morphological and TE properties of AJ-printed nanocomposite structures were then evaluated as a function of the composition so that optimum ink formulation and printing conditions could be found to maximise the final TE performance. Importantly, these TE nanocomposites were found to be particularly stable and robust upon repeated flexing. They can be directly integrated into high-performance TEGs with minimal post-possessing treatment, making them particularly suitable for flexible TE applications. Subsequently, multiwall carbon nanotubes (MWCNTs) were introduced to enhance σ of AJ-printed nanocomposites, thereby achieving even higher PF values. A novel in situ mixing method was capable of simultaneously incorporating high-S Sb2Te3 nanoflakes and high-σ MWCNTs that could provide good inter-particle connectivity, to significantly enhance the TE performance of PEDOT:PSS. Rigorous flexing and fatigue tests also confirmed the excellent mechanical robustness and stability of these AJ-printed MWCNTs-based TE nanocomposites. The added MWCNTs have led to not only higher σ, but they also have improved the mechanical flexibility and fatigue robustness of the resulting nanocomposites. Since the ZT and PF of TE materials often have a strong dependence on temperature, a single TE material spanning a given temperature range is unlikely to have an optimal ZT or PF across the entire range, leading to the inefficient TEG performance. The temperature-dependent TE properties of AJ-printed TE nanocomposites were therefore studied as a function of the loading fraction, with a view to enhancing the overall TE performance of a TEG by varying its composition accordingly across a given temperature range. For the first time, compositionally graded thermoelectric composites (CG-TECs) have been developed and shown to improve TE performance over TEGs having a single composition across the same temperature range. The composition of the TE nanocomposite was systematically tuned along the length of the TEG in order to optimise the PF along the temperature gradient between which it operates. Lastly, the AJP technique was used to fabricate free-standing and stretchable TE structures, by printing serpentine patterns of the TE ink onto a sacrificial substrate that was subsequently removed. The TE performance and stretchability under different imposed mechanical conditions were evaluated, including testing for the reliability of prolonged stretching cycles. The CG-TEC concept was also incorporated into the stretchable structure to achieve further improvement of TE performance.China Scholarship Council and Cambridge Commonwealth, European and International Trus

Versatile Fabrication Methods for Wearable Thermo-electrochemical Cells

Emerging markets for wearable electronics have stimulated a rapidly growing demand for the commercialisation of flexible and reliable energy storage and conversion units, which includes batteries, supercapacitors, and thermo-electrochemical cells (thermocell). Among them, thermocell have attracted significant research attention in recent years owing to their ability to continuously convert body heat into electrical energy. The commercial viability of wearable thermocells has long been limited by their low power output and complex fabrication methods. Great progress has been made in developing flexible electrode materials, gel electrolytes and encapsulation materials. However, it is still a main challenge to develop flexible electrodes on a various-scale and in a cost-effective manner. At present, carbon electrodes are commonly fabricated using a vacuum filtration method. However, fine carbon nanoparticles can be drawn through the filter paper pores via suction force, resulting in blockage of the filtrate and wastage of the ink materials. Meanwhile, this fabrication method is time consuming and reduces the overall fabrication efficiency of devices. Therefore, additional fabrication methods exert pressure on developing simple and scalable techniques, such as laser-etching, 3D printing, and drop coating. The main goal for this study is to fabricate high performance electrodes for wearable thermocell devices in simple and scalable ways. A wearable poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS or PEDOT: PSS) based film was firstly prepared via a laser-etching method and assembled to be wearable all-solid-state thermocell. For applications of this wearable thermocell, a flexible watch-strap shaped thermocell that could harvest body heat, charge supercapacitors, and light a green LED. This systematic investigation and optimization of 3D structured laser-etched electrode, gel electrolyte, and device architectures introduced has great significance for the realization of body heat harvesting and application in real self-powered wearable electronics

Nanoplasmonics In Two-dimensional Dirac and Three-dimensional Metallic Nanostructure Systems

Surface plasmons are collective oscillation of electrons which are coupled to the incident electric field. Excitation of surface plasmon is a route to engineer the behavior of light in nanometer length scale and amplifying the light-matter interaction. This interaction is an outcome of near-field enhancement close to the metal surface which leads to plasmon damping through radiative decay to outgoing photons and nonradiative decay inside and on the surface of the material to create an electron-hole pair via interband or intraband Landau damping. Plasmonics in Dirac systems such as graphene show novel features due to massless electrons and holes around the Dirac cones. Linear band structure of Dirac materials in the low-momentum limit gives rise to the unprecedented optical and electrical properties. Electronical tunability of the plasmon resonance frequency through applying a gate voltage, highly confined electric field, and low plasmon damping are the other special propoerties of the Dirac plasmons. In this work, I will summarize the theoretical and experimental aspects of the electrostatical tunable systems made from monolayer graphene working in mid-infrared regime. I will demonstrate how a cavity-coupled nanopatterned graphene excites Dirac plasmons and enhances the light-matter interaction. The resonance frequency of the Dirac plasmons is tunable by applying a gate voltage. I will show how different gate-dielectrics, and the external conditions like the polarization and angle of incident light affect on the optical response of the nanostructure systems. I will then show the application of these nanodevices in infrared detection at room temperature by using plasmon-assisted hot carriers generation. An asymmetric nanopatterned graphene shows a high responsivity at room temperature which is unprecedented. At the end, I will demonstrate the properties of surface plasmons on 3D noble metals and its applications in light-funneling, photodetection, and light-focusing

New concepts in energy and mass transport within carbon nanotubes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 164-177).The unique structure of carbon nanotubes (CNTs) contributes to their distinguished properties, making them useful in nanotechnology. CNTs have been explored for energy transport in next-generation, such as light-emitting diodes, field-effect transistors, and phonon wave guides due to their high axial electrical and thermal conductivity. Also, their subnanometer scale with atomically smooth surfaces is promising for selective mass transport in nanoscale, such as molecular transport, selective gas permeation, and nanofluidics. The first part of this thesis considers CNTs as substrates for guided chemical reactivity and thermal waves for energy generation. Coupling an exothermic chemical reaction with a nanowire possessing a high axial thermal conductivity creates a self-propagating reactive wave. Such waves are realized using a 7-nm cyclotrimethylene-trinitramine (TNA) annular shell around a CNT and are amplified by 104 times the bulk TNA value, propagating more than 2 m/s, with an effective thermal conductivity of 1.28 ± 0.2 kW/m/K at 2860 K. Thermally excited carriers in the direction of the propagating reaction produces a concomitant electrical pulse of high specific power, as large as 7 kW/kg, that we identify as a thermopower wave. The specific power increases with a decreasing system size, resulting in usually efficient sub-micron and nano-sized pulse power sources. In the second portion, we develop a nanopore platform using the interior of a single walled carbon nanotube (SWNT) for study of single ion transport. Such pores can undergo a resonance in ion transport such that coherent waveforms are generated (CR). The asymmetric electrostatic barriers at their ends show that above the threshold bias, traversing the nanopore end is not rate limiting and that the pore blocking behavior of two parallel nanotubes follows an idealized Markov process. We report two channels undergoing this CR simultaneously, the dynamics of ion transport for different cations (Li+, Na+, K+, Cs+) and the effect of varying the applied voltage on transport across the SWNT channel. Finally, the diameter and temperature dependence (1-2 nm) of ion transport shows the distinct trend in dwell time and blockade current that study its transfer mechanism by proton 'hop' and 'turn', and single ion transport.by Wonjoon Choi.Ph.D

Quantum theory of electronic and thermal transport through nano-scale and single-molecule devices

This thesis presents a series of studies into the electronic, thermal and thermoelectric properties of molecular junctions containing single organic molecules. The exploration and understanding the electronic and phononic characteristics of molecules connected to metallic leads is a vital part of nanoscience if molecular electronics is to have a future. This thesis documents a study for various families of organic and organometallic molecules, studied using a combination of density functional theory (DFT), which is implemented in the SIESTA code, and the Green’s function formalism of transport theory. The main results of this thesis are as follows: To elucidate the nature of the high and low conductance groups observed in break-junction measurements of single 4,4-bipyridine molecules, I present a combined experimental and theoretical study of the electrical conductance of a family of 4,4-bipyridine molecules, with a series of sterically-induced twist angles α between the two pyridyl rings. I show that their conductances are proportional to cos2(α), confirming that pi-pi overlap between adjacent rings plays a dominant role. Since both peaks exhibit a cos2 (α) dependence of conductance on torsion angle, this is evidence that the high and low conductances correspond to molecular orientations within the junctions, in which the electrical current passes through the C-C bond linking the pi systems of the two rings. Furthermore, this result demonstrates that the Fermi energy is located within the HOMO-LUMO gap and not close to a transmission resonance. A theoretical investigation into the Seebeck coefficient in pi-stacked molecular junctions is performed using a first principles quantum transport method. Using oligo (phenyleneethynylene) (OPE)-type molecules as a model system, I show that quantum interference produces anti-resonances in the gap between the HOMO and LUMO resonances and the stacking geometry can control the position of this quantum interference feature. The shifting of this resonance enhances the thermopower S is expected when the junction is tuned through a node in the transmission function. We found supramolecular π-π interactions between two molecules changed the sign of thermopower. I have investigated a family molecules with various side branched atoms to study the electron and phonon transport through nanoscale molecular junctions, with a view to understanding the performance thermoelectric materials. My calculations focus on the effect of heteroatoms formed from C, Si, Ge, and Sn on the thermal phonon conductance, electrical conductance, and Seebeck Coefficient. I also examine how the thermoelectric figure of merit is affected by side branched atoms, as the bond length and mass play an important role in determining the thermal phonon conductance of molecular wires. Due to the rigid nature of C-side branching, the thermal phonon conductance decreases monotonically with the bond length and mass, whereas thermal phonon conductance with Si-side branches increases with the length of the bond and mass. The low thermal conductance kel with S-bridging, combined with their higher thermopower and higher electrical conductance leads to a maximum thermoelectric figure of merit of ZT = 1.76, which is several orders of magnitude higher than that of bridges