Browsing by Author "Baughman, Ray H."

Now showing 1 - 20 of 23

A Multiscale Model to Study the Enhancement in the Compressive Strength of Multi-Walled CNT Sheet Overwrapped Carbon Fiber Composites
(Elsevier Ltd) Ravindranath, P. K.; Roy, S.; Unnikrishnan, V.; Wang, X.; Xu, Tingge; Baughman, Ray H.; Lu, Hongbing; 0000-0001-5845-5137 (Baughman, RH); Xu, Tingge; Baughman, Ray H.; Lu, Hongbing
The high tensile strength of polymer matrix composites is derived primarily from the high strength of the carbon fibers embedded in the polymer matrix. However, their compressive strength is generally much lower due to the fact that under compression, the fibers tend to fail through micro-buckling well before compressive fracture occurs. In this work, we consider multi-walled carbon nanotube (MWNT) sheets wrapped around carbon fiber at room temperature to improve fiber/matrix interfacial properties which, in turn, influences compressive strength of the composite. To investigate the effect of the wrapping of MWNT sheet on composite strength, Molecular Dynamics simulations were performed on an atomistic model of the interface region between the epoxy, carbon fiber and the scrolled MWNT sheets. The compressive strength of the unidirectional composite was computed using a novel hierarchical multi-scale model comprising of the rule of mixtures at the microscale, and the modified Argon's formula for composites at the macroscale. Model predictions were benchmarked through comparison with experimental data for different volume fractions of MWNT sheet. ©2019 Elsevier Ltd
Bio-Inspired, Moisture-Powered Hybrid Carbon Nanotube Yarn Muscles
Kim, Shi Hyeong; Kwon, Cheong Hoon; Park, Karam; Mun, Tae Jin; Lepro, Xavier; Baughman, Ray H.; Spinks, Geoffrey M.; Kim, Seon Jeong; 0000 0003 5232 4253 (Baughman, RH); 0000-0002-0166-3127 (Lepró, X); Lepró, Xavier; Baughman, Ray H.
Hygromorph artificial muscles are attractive as self-powered actuators driven by moisture from the ambient environment. Previously reported hygromorph muscles have been largely limited to bending or torsional motions or as tensile actuators with low work and energy densities. Herein, we developed a hybrid yarn artificial muscle with a unique coiled and wrinkled structure, which can be actuated by either changing relative humidity or contact with water. The muscle provides a large tensile stroke (up to 78%) and a high maximum gravimetric work capacity during contraction (2.17 kJ kg⁻¹), which is over 50 times that of the same weight human muscle and 5.5 times higher than for the same weight spider silk, which is the previous record holder for a moisture driven muscle. We demonstrate an automatic ventilation system that is operated by the tensile actuation of the hybrid muscles caused by dew condensing on the hybrid yarn. This self-powered humidity-controlled ventilation system could be adapted to automatically control the desired relative humidity of an enclosed space.
Biothermal Sensing of a Torsional Artificial Muscle
(Royal Soc Chemistry, 2016-01-25) Lee, Sung-Ho; Kim, Tae Hyeob; Lima, M©rcio D.; Baughman, Ray H.; Kim, Seon Jeong; 0000 0003 5232 4253 (Baughman, RH); Lima, M©rcio D.; Baughman, Ray H.
Biomolecule responsive materials have been studied intensively for use in biomedical applications as smart systems because of their unique property of responding to specific biomolecules under mild conditions. However, these materials have some challenging drawbacks that limit further practical application, including their speed of response and mechanical properties, because most are based on hydrogels. Here, we present a fast, mechanically robust biscrolled twist-spun carbon nanotube yarn as a torsional artificial muscle through entrapping an enzyme linked to a thermally sensitive hydrogel, poly(N-isopropylacrylamide), utilizing the exothermic catalytic reaction of the enzyme. The induced rotation reached an equilibrated angle in less than 2 min under mild temperature conditions (25-37 ⁰C) while maintaining the mechanical properties originating from the carbon nanotubes. This biothermal sensing of a torsional artificial muscle offers a versatile platform for the recognition of various types of biomolecules by replacing the enzyme, because an exothermic reaction is a general property accompanying a biochemical transformation.
Conductive Functional Biscrolled Polymer and Carbon Nanotube Yarns
(2013-10-10) Kim, S. H.; Sim, H. J.; Shin, M. K.; Choi, A. Y.; Kim, Y. T.; Lima, Marcio D.; Baughman, Ray H.; Kim, S. J.; 0000 0003 5232 4253 (Baughman, RH); Lima, Marcio D.; Baughman, Ray H.
Biscrolling aligned electrospun fiber (AEF) sheets and carbon nanotube (CNT) sheets were fabricated for conductive, functional yarns by a versatile dry composite method. Our biscrolling (twist-based spinning) method is based on spinnable polymer fiber sheets and spinnable CNT sheets unlike the previous biscrolling technique using unspinnable nanopowders and spinnable CNT sheets. The CNT sheet in composite yarns acted as effective electrical wires forming dual Archimedean multilayer rolled-up nanostructures. The weight percent of the electrospun polymer fibers in the composite yarns was over 98%, and the electrical conductivity values of the composite yarns was 3 orders higher than those of other non-conducting polymer/CNT composite fibers which were electrospun from polymer solutions containing similar loading of CNTs. We also demonstrate that biscrolled yarns having various structures can be fabricated from spinnable AEF sheets and spinnable CNT sheets.
Enhancement of Electromagnetic Interference Shielding Effectiveness with Alignment of Spinnable Multiwalled Carbon Nanotubes
(Pergamon-Elsevier Science Ltd, 2018-10-23) Lee, Duck Weon; Park, Jongwoo; Kim, Bum Joon; Kim, Hyunsoo; Choi, Changsoon; Baughman, Ray H.; Kim, Seon Jeong; Kim, Youn Tae; 0000-0001-5845-5137 (Baughman, RH); Baughman, Ray H.
This research develops a unique material to attenuate electromagnetic interference (EMI) by using spinnable multiwalled carbon nanotubes (MWNTs) combined with bio-polydimethylsiloxane (PDMS) that contains BaTiO₃ (MBPBT). In particular, a plaid pattern, formed by the spinnable MWNTs, is very effective in attenuating the propagation of EM waves, which achieves over 20 dB at 8.2-12.4 GHz (X-band frequency range). This means that a filter type of the spinnable MWNTs is actively able to handle the directionality and movement of EMI propagation. In addition, the MBPBT is characterized by its strong mechanical advantage (bending radius 180 degrees).
Enhancing the Strength, Toughness, and Electrical Conductivity of Twist-Spun Carbon Nanotube Yarns by π Bridging
(Elsevier Ltd, 2019-05-10) Liang, X.; Gao, Y.; Duan, J.; Liu, Z.; Fang, Shaoli; Baughman, Ray H.; Jiang, L.; Cheng, Q.; Fang, Shaoli; Baughman, Ray H.
The weak interfacial interactions between carbon nanotube (CNT) always results in low stress load transfer efficiency in CNT yarns, herein we fabricated strong, highly conducting CNT yarns at room temperature using molecules having aromatic end groups, π bridging neighboring CNTs. The resulting CNT yarns have high tensile strength with 1697 ± 24 MPa, toughness with 18.6 ± 1.6 MJ/m³, and electrical conductivity with 656.2 S/cm, which are 3.9, 2.5, and 3.5 times, respectively, as high as that of the neat CNT yarn. The specific tensile strength of the resulting CNT yarn is higher than that for previously reported CNT yarns fabricated at room temperature, even that for some CNT yarns fabricated using corossive environments or extreme temperature. This π bridging strategy provides a promising avenue for fabricating high performance CNT yarns under ambient conditions. ©2019 Elsevier Ltd
Enhancing the Work Capacity of Electrochemical Artificial Muscles by Coiling Plies of Twist-Released Carbon Nanotube Yarns
(American Chemical Society) Kim, K. J.; Hyeon, J. S.; Kim, H.; Mun, T. J.; Haines, Carter S.; Li, Na; Baughman, Ray H.; Kim, S. J.; 0000-0001-5845-5137 (Baughman, RH); Haines, Carter S.; Li, Na; Baughman, Ray H.
Twisted-yarn-based artificial muscles can potentially be used in diverse applications, such as valves in microfluidic devices, smart textiles, air vehicles, and exoskeletons, because of their high torsional and tensile strokes, high work capacities, and long cycle life. Here, we demonstrate electrochemically powered, hierarchically twisted carbon nanotube yarn artificial muscles that have a contractile work capacity of 3.78 kJ/kg, which is 95 times the work capacity of mammalian skeletal muscles. This record work capacity and a tensile stroke of 15.1% were obtained by maximizing yarn capacitance by optimizing the degree of inserted twist in component yarns that are plied until fully coiled. These electrochemically driven artificial muscles can be operated in reverse as mechanical energy harvesters that need no externally applied bias. In aqueous sodium chloride electrolyte, a peak electrical output power of 0.65 W/kg of energy harvester was generated by 1 Hz sinusoidal elongation. ©2019 American Chemical Society.
Harvesting Electrical Energy from Torsional Thermal Actuation Driven by Natural Convection
(Nature Publishing Group) Kim, Shi Hyeong; Sim, Hyeon Jun; Hyeon, Jae Sang; Suh, Dongseok; Spinks, Geoffrey M.; Baughman, Ray H.; Kim, Seon Jeong; 0000-0001-5845-5137 (Baughman, RH); Baughman, Ray H.; Kim, Seon Jeong
The development of practical, cost-effective systems for the conversion of low-grade waste heat to electrical energy is an important area of renewable energy research. We here demonstrate a thermal energy harvester that is driven by the small temperature fluctuations provided by natural convection. This harvester uses coiled yarn artificial muscles, comprising well-aligned shape memory polyurethane (SMPU) microfibers, to convert thermal energy to torsional mechanical energy, which is then electromagnetically converted to electrical energy. Temperature fluctuations in a yarn muscle, having a maximum hot-to- cold temperature difference of about 13 ⁰C, were used to spin a magnetic rotor to a peak torsional rotation speed of 3,000 rpm. The electromagnetic energy generator converted the torsional energy to electrical energy, thereby producing an oscillating output voltage of up to 0.81 V and peak power of 4 W/kg, based on SMPU mass.
Harvesting Temperature Fluctuations as Electrical Energy Using Torsional and Tensile Polymer Muscles
(Royal Soc Chemistry, 2015-09-28) Kim, Shi Hyeong; Lima, M©rcio D.; Kozlov, Mikhail E.; Haines, Carter S.; Spinks, Geoffrey M.; Aziz, Shazed; Choi, Changsoon; Sim, Hyeon Jun; Wang, Xuemin; Lu, Hongbing; Qian, Dong; Madden, John D. W.; Baughman, Ray H.; Kim, Seon Jeong; 0000 0003 5232 4253 (Baughman, RH); Lima, M©rcio D.; Kozlov, Mikhail E.; Wang, Xuemin; Lu, Hongbing; Qian, Dong; Baughman, Ray H.
Diverse means have been deployed for harvesting electrical energy from mechanical actuation produced by low-grade waste heat, but cycle rate, energy-per-cycle, device size and weight, or cost have limited applications. We report the electromagnetic harvesting of thermal energy as electrical energy using thermally powered torsional and tensile artificial muscles made from inexpensive polymer fibers used for fishing line and sewing thread. We show that a coiled 27 μm-diameter nylon muscle fiber can be driven by 16.7 ⁰C air temperature fluctuations to spin a magnetic rotor to a peak torsional rotation speed of 70000 rpm for over 300000 heating-cooling cycles without performance degradation. By employing resonant fluctuations in air temperature of 19.6 ⁰C, an average output electrical power of 124 W per kg of muscle was realized. Using tensile actuation of polyethylene-based coiled muscles and alternating flows of hot and cold water, up to 1.4 J of electrical energy was produced per cycle. The corresponding per cycle electric energy and peak power output, per muscle weight, were 77 J kg⁻¹ and 28 W kg⁻¹, respectively.
High-Performance Biscrolled MXene/Carbon Nanotube Yarn Supercapacitors
(Wiley-VCH Verlag) Wang, Z.; Qin, S.; Seyedin, S.; Zhang, J.; Wang, J.; Levitt, A.; Li, Na; Haines, Carter; Ovalle-Robles, R.; Lei, W.; Gogotsi, Y.; Baughman, Ray H.; Razal, J. M.; 0000 0003 5232 4253 (Baughman, RH); 0000-0001-5845-5137 (Baughman, RH); Li, Na; Haines, Carter; Baughman, Ray H.
Yarn-shaped supercapacitors (YSCs) once integrated into fabrics provide promising energy storage solutions to the increasing demand of wearable and portable electronics. In such device format, however, it is a challenge to achieve outstanding electrochemical performance without compromising flexibility. Here, MXene-based YSCs that exhibit both flexibility and superior energy storage performance by employing a biscrolling approach to create flexible yarns from highly delaminated and pseudocapacitive MXene sheets that are trapped within helical yarn corridors are reported. With specific capacitance and energy and power densities values exceeding those reported for any YSCs, this work illustrates that biscrolled MXene yarns can potentially provide the conformal energy solution for powering electronics beyond just the form factor of flexible YSCs.
Highly Stretchable Hybrid Nanomembrane Supercapacitors
(2016-03-04) Kim, Keon Jung; Lee, Jae Ah (UT Dallas); Lima, Márcio D. (UT Dallas); Baughman, Ray H.; Kim, Seon Jeong; 0000 0003 5232 4253 (Baughman, RH); Baughman, Ray H.
Supercapacitors that are lightweight, mechanically deformable (stretchable, flexible) and electrochemically stable have potential for various applications like portable, wearable, and implantable electronics. Here we demonstrate a stretchable and high-performing hybrid nanomembrane supercapacitor. The hybrid nanomembrane is prepared by vapour phase polymerization (VPP) based nanoscopic PEDOT coating on carbon nanotube sheets (CNS) transferred onto an elastomeric substrate to form a wavy structure. The resulting wavy structured hybrid nanomembrane based supercapacitor exhibits high electrochemical performance and mechanical stretchability, simultaneously. The high specific capacitances and energy density (82 F g⁻¹, 11 mF cm⁻², and 7.28 W h kg⁻¹ at 0% strain) are retained under large mechanical deformation (77 F g⁻¹ and 6.87 W h kg⁻¹ at a biaxial strain of 600%). Moreover, there is only <1% degradation of capacitance ratio after 1000 cycles stretching/releasing and bending/unbending. This high mechanical cyclic stability is shown even during stretching/releasing and bending/unbending measured by dynamic cyclic voltammetry (CV). These results suggest that our supercapacitor is valuable in a wide range of applications that require it to be electrochemically stable under large mechanical deformation, such as strain sensors, wearable electronics and biomedical devices.
Magnetic Torsional Actuation of Carbon Nanotube Yarn Artificial Muscle
(Royal Society of Chemistry) Lee, D. W.; Kim, S. H.; Kozlov, Mikhail E.; Lepró, Xavier; Baughman, Ray H.; Kim, S. J.; 0000 0003 5232 4253 (Baughman, RH); 0000-0002-0166-3127 (Lepró, X); 0000-0001-5845-5137 (Baughman, RH); Kozlov, Mikhail E.; Lepró, Xavier; Baughman, Ray H.
Magnetically driven torsional actuation of a multiwalled carbon nanotube (MWNT) yarn was realized by first biscrolling NdFeB magnetic particles into helical yarn corridors to make a magnetic MWNT yarn. The actuating device comprised a pristineMWNT yarn that was connected to the magnetic MWNT yarn, with a paddle attached between these yarns. The application of a magnetic field reversibly drove torsional actuation of up to 80° within ∼0.67 seconds. This magnetic actuator was remotely powered, and its actuation stroke was the same when the muscle array was at 20 °C and at -100 °C.
Multifunctional Carbon Nanotube Yarns for Artificial Muscles and Energy Harvesters
(2021-08-01T05:00:00.000Z) Wang, Zhong; Baughman, Ray H.; Da Silveira Rodrigues, Fabiano; Zakhidov, Anvar A.; Ferrairs, John P.; Pantano, Paul
The superb mechanical, physical, and chemical properties of carbon nanotube (CNT) yarns have promoted their application as function components that program actuation, sensing, and power management for soft robotics and smart systems. Success in making artificial muscles that are faster, more powerful, and that can provide larger strokes would expand their applications. Efficient conversion of ambient mechanical energy into electrical energy is needed for diverse applications, including self-powered wireless sensors, structural and human health monitoring systems, and the extraction of energy from ocean waves. Herein, the development of CNT yarn artificial muscles and mechanical energy harvesters are first discussed, and the obtained understanding of underlying mechanisms provide guidance for optimizing muscle and harvester performances. Next, unipolar stroke CNT yarn muscles are described, in which muscle stroke changes between extreme potentials are additive and muscle stroke remarkably increases with increasing potential scan rate. The normal decrease in stroke with increasing scan rate, because of decreased capacitance, is overwhelmed by a dramatic increase in effective ion size caused by electroosmotic pumping of solvent. These coiled carbon nanotube yarn muscles contain a yarn guest that shifts the yarn’s potential of zero charge (pzc) by over a volt, either positively or negatively. Such pzc shift agents include ion-exchange membrane polymers, oxidized graphene platelets, and surfactants. Record muscle strokes, contractile work-per-cycle, contractile power densities, and energy conversion efficiencies are obtained for unipolar muscles. Then, powerful CNT yarn mechanical energy harvesters (we call twistrons) are described, which are electrochemical artificial muscles run in reverse. Stretching a coiled CNT yarn can provide large, reversible changes in electrochemical capacitance, which enables conversion of mechanical energy to electrical energy. The performance of these twistron harvesters can be increased by diverse fabrication methods: optimizing the structure of the precursor CNT forest, using stretchinduced alignment, thermal annealing under tension, and incorporating reduced graphene oxide nanoplates. The peak output power at 1 Hz and at 30 Hz for a sinusoidal stretch were 0.73 and 3.19 kW/kg, which are 15- and 13-fold higher than for previous twistron harvesters at these respective frequencies. This performance at 30 Hz was over 12-fold that of other prior-art mechanical energy harvesters for frequencies between 1 Hz and 600 Hz. Last, the opportunities and challenges for future practical applications of CNT yarns are highlighted.
A New Catalyst-Embedded Hierarchical Air Electrode For High-Performance Li-O₂ Batteries
(2013-06-05) Lim, H. -D; Song, H.; Gwon, H.; Park, K. -Y; Kim, J.; Bae, Y.; Kim, H.; Jung, S. -K; Kim, T.; Kim, Y. H.; Lepr©, Xavier; Ovalle-Robles, Raquel; Baughman, Ray H.; Kang, K.; 0000 0003 5232 4253 (Baughman, RH); Lepr©, Xavier; Ovalle-Robles, Raquel; Baughman, Ray H.
The Li-O₂ battery holds great promise as an ultra-high-energy- density device. However, its limited rechargeability and low energy efficiency remain key barriers to its practical application. Herein, we demonstrate that the ideal electrode morphology design combined with effective catalyst decoration can enhance the rechargeability of the Li-O₂ battery over 100 cycles with full discharge and charge. An aligned carbon structure with a hierarchical micro-nano-mesh ensures facile accessibility of reaction products and provides the optimal catalytic conditions for the Pt catalyst. The new electrode is highly reversible even at the extremely high current rate of 2 A g⁻¹. Moreover, we observed clearly distinct morphologies of discharge products when the catalyst is used. The effect of catalysts on the cycle stability is discussed.
Nylon-Muscle-Actuated Robotic Finger
(SPIE--International Society of Optical Engineering) Wu, Lianjun; de Andrade, Monica Jung; Rome, Richard S.; Haines, Carter; Lima, Marcio D.; Baughman, Ray H.; Tadesse, Yonas; Wu, Lianjun; de Andrade, Monica Jung; Rome, Richard S.; Haines, Carter; Lima, Marcio D.; Baughman, Ray H.; Tadesse, Yonas
This paper describes the design and experimental analysis of novel artificial muscles, made of twisted and coiled nylon fibers, for powering a biomimetic robotic hand. The design is based on circulating hot and cold water to actuate the artificial muscles and obtain fast finger movements. The actuation system consists of a spring and a coiled muscle within a compliant silicone tube. The silicone tube provides a watertight, expansible compartment within which the coiled muscle contracts when heated and expands when cooled. The fabrication and characterization of the actuating system are discussed in detail. The performance of the coiled muscle fiber in embedded conditions and the related characteristics of the actuated robotic finger are described.
Orthogonal Pattern of Spinnable Multiwall Carbon Nanotubes for Electromagnetic Interference Shielding Effectiveness
(Elsevier Ltd, 2019-05-022) Lee, D. W.; Kim, H.; Moon, J. H.; Jeong, J. -H; Sim, H. J.; Kim, B. J.; Hyeon, J. S.; Baughman, Ray H.; Kim, S. J.; 0000-0001-5845-5137 (Baughman, RH); Baughman, Ray H.
The need for thin and lightweight electromagnetic interference shielding materials is rapidly increasing in several industries, such as aerospace and telecommunication. This research finds that a shielding material, which is developed by the orthogonal pattern of spinnable multiwall carbon nanotubes (MWNTs), is ultra-light weight, thin, and has a high shielding effectiveness (SE). An orthogonal pattern, generated by just alignment of the spinnable MWNTs without adding any support materials such as polymers, ceramics, and magnets demonstrates that it is possible to efficiently attenuate electromagnetic interference (EMI) in the X-band frequency range (8.2–12.4 GHz). EMI SE in the developed shielding material is about 19.2 dB with a specific shielding effectiveness (SSE)/t (thickness) value of 73,633 dB cm² g⁻¹ at a thickness of about 4.48 μm. In addition, absorption effectiveness in this shielding material is as high as 96.3%, which provides excellent ability to reduce the secondary damage by reflection. ©2019 Elsevier Ltd
Precessional Effects on Gravitational Wave Data Analysis
(2023-05) Stoikos, Evangelos 1993-; Kesden, Michael; King, Lindsay J.; Baughman, Ray H.; Ishak-Boushaki, Mustapha; Gartstein, Yuri; Penev, Kaloyan
Black holes (BHs) that closely orbit each other can form a binary black hole (BBH) system. We can divide the lifetime of these BBH systems into three distinct phases: the adiabatic inspiral, the merger and the ringdown. BBHs can emit gravitational waves (GW) during every phase of their lifetimes. The spins of the individual BHs are expected to have non-zero values and to be misaligned with the orbital angular momentum. This misalignment can induce precession and nutation of the orbital angular momentum around the total angular momentum. These phenomena modify the GW phase and amplitude. Efforts are underway to quantify these effects via two spin parameters, χeff, χp, inside post-Newtonian (PN) templates used in parameter-estimation methods. There are claims that precession has been detected both statistically in the third observing run(O3) catalog, and in individual systems like GW200129 but the consensus is not yet clear. We quantify precession and nutation by introducing five new parameters. We believe these parameters may provide a more complete characterization of the amplitude and frequency of precession and nutation as binaries inspiral through the sensitivity band of GW detectors. We introduce the parameters inside a PN template and study the modulation of the GWs. We then calculate the mismatch between templates to determine the minimum signal-to-noise needed to identify precession and in both the next LIGO collaboration runs as well as proposed future detectors. Then we move on to the strong gravitational lensing of GWs which occurs when the GWs from a compact binary system travel near a massive object. The lensed waveform is given by the product of the lensing amplification factor F and the unlensed waveform. In the geometrical-optics approximation, lensing produces at most two discrete images which can be parameterized by two image parameters, the flux ratio I and time delay ∆td between images. In the macrolensing regime for which ∆td is large compared to the time T they spend within the sensitivity band of GW detectors, it is natural to parameterize lensing searches in terms of these image parameters. The functional dependence of the lensed signal on these image parameters is far simpler, facilitating data analysis for events with modest signal-to-noise ratios, and constraints on I and ∆td can be found. We then propose that this use of image parameters can be extended to the microlensing regime (∆td < T) in which the two interfering images are observed as a single GW event. Finally, we use image parameters to determine the detectability of gravitational lensing in GW the microlensing regime.
Probe Sensor Using Nanostructured Multi-Walled Carbon Nanotube Yarn for Selective and Sensitive Detection of Dopamine
(MDPI AG) Al-Graiti, Wed; Yue, Zhilian; Foroughi, Javad; Huang, Xu-Feng; Wallace, Gordon; Baughman, Ray H.; Chen, Jun; 0000 0003 5232 4253 (Baughman, RH); Baughman, Ray H.
The demands for electrochemical sensor materials with high strength and durability in physiological conditions continue to grow and novel approaches are being enabled by the advent of new electromaterials and novel fabrication technologies. Herein, we demonstrate a probe-style electrochemical sensor using highly flexible and conductive multi-walled carbon nanotubes (MWNT) yarns. The MWNT yarn-based sensors can be fabricated onto micro Pt-wire with a controlled diameter varying from 100 to 300 mu m, and then further modified with Nafion via a dip-coating approach. The fabricated micro-sized sensors were characterized by electron microscopy, Raman, FTIR, electrical, and electrochemical measurements. For the first time, the MWNT/Nafion yarn-based probe sensors have been assembled and assessed for high-performance dopamine sensing, showing a significant improvement in both sensitivity and selectivity in dopamine detection in presence of ascorbic acid and uric acid. It offers the potential to be further developed as implantable probe sensors.
Sequentially Bridged Graphene Sheets with High Strength, Toughness, and Electrical Conductivity
(National Academy of Sciences) Wan, S.; Li, Y.; Mu, Jiuke; Aliev, Ali E.; Fang, Shaoli; Kotov, N. A.; Jiang, L.; Cheng, Q.; Baughman, Ray H.; Mu, Jiuke; Aliev, Ali E.; Fang, Shaoli; Baughman, Ray H.
We here show that infiltrated bridging agents can convert inexpensively fabricated graphene platelet sheets into high-performance materials, thereby avoiding the need for a polymer matrix. Two types of bridging agents were investigated for interconnecting graphene sheets, which attach to sheets by either π–π bonding or covalent bonding. When applied alone, the π–π bonding agent is most effective. However, successive application of the optimized ratio of π–π bonding and covalent bonding agents provides graphene sheets with the highest strength, toughness, fatigue resistance, electrical conductivity, electromagnetic interference shielding efficiency, and resistance to ultrasonic dissolution. Raman spectroscopy measurements of stress transfer to graphene platelets allow us to decipher the mechanisms of property improvement. In addition, the degree of orientation of graphene platelets increases with increasing effectiveness of the bonding agents, and the interlayer spacing increases. Compared with other materials that are strong in all directions within a sheet, the realized tensile strength (945 MPa) of the resin-free graphene platelet sheets was higher than for carbon nanotube or graphene platelet composites, and comparable to that of commercially available carbon fiber composites. The toughness of these composites, containing the combination of π–π bonding and covalent bonding, was much higher than for these other materials having high strengths for all in-plane directions, thereby opening the path to materials design of layered nanocomposites using multiple types of quantitatively engineered chemical bonds between nanoscale building blocks.
Terahertz Surface Plasmon Polaritons on Freestanding Multi-Walled Carbon Nanotube Aerogel Sheets
(2012-05-08) Nguyen, T. D.; Liu, S.; Lima, Marcio Dias; Fang, Shaoli; Baughman, Ray H.; Nahata, A.; Vardeny, Z. V.; 0000 0003 5232 4253 (Baughman, RH); Lima, Marcio Dias; Fang, Shaoli; Baughman, Ray H.
We demonstrate that multi-walled carbon nanotubes (MWCNTs) are capable of supporting surface plasmon-polaritons (SPPs) at terahertz (THz) frequencies. To achieve this, we fabricated sub-100 μm-thick freestanding and highly oriented multi-walled carbon nanotube (MWCNT) aerogel sheets. Utilizing terahertz time-domain spectroscopy, we measured the complex index of refraction of the sheets for two orthogonal nanotube orientations. We found that the MWCNT sheets exhibit highly anisotropic THz polarization behavior. Based on the extracted dielectric properties of the medium, which show that it exhibits metallic behavior in the THz spectral range, we investigated the existence and propagation of SPPs by studying the resonantly enhanced transmission through periodic MWCNT hole arrays. We found that carbon nanotubes support SPP excitations that propagate along the tubes, but highly suppress these surface waves in the direction perpendicular to the nanotubes.