Ray Baughman | University of Texas at Dallas (original) (raw)
Papers by Ray Baughman
arXiv (Cornell University), Jan 18, 2019
Journal of Applied Physics, Mar 31, 2004
Nanotube sheets, or ''bucky papers,'' have been proposed for use in actuating, structural and ele... more Nanotube sheets, or ''bucky papers,'' have been proposed for use in actuating, structural and electrochemical systems, based in part on their potential mechanical properties. Here, we present results of detailed simulations of networks of nanotubes/ropes, with special emphasis on the effect of joint morphology. We perform detailed simulations of three-dimensional joint deformation, and use the results to inform simulations of two-dimensional ͑2D͒ networks with intertube connections represented by torsion springs. Upper bounds are established on moduli of nanotube sheets, using the 2D Euler beam-network simulations. Comparisons of experimental and simulated response for HiPco-nanotube and laser-ablated nanotube sheets, indicate that ϳ2-30-fold increases in moduli may be achievable in these materials. Increasing the numbers of interrope connections appears to be the best target for improving nanotube sheet stiffnesses in materials containing straight segments.
Physical review, Feb 15, 1990
Structural models for a stage-2 complex are proposed for polyacetylene doped with less than about... more Structural models for a stage-2 complex are proposed for polyacetylene doped with less than about 0.1 potassium or rubidium atoms per carbon. These structures utilize as a basic motif an alkali-metal column surrounded by four planar-zigzag polyacetylene chains, a structure found at the highest dopant levels. In the new stage-2 structures, each polyacetylene chain neighbors only one alkali-metal column, so the phase contains four polymer chains per alkali-metal column. Basic structural aspects for stage-1 and stage-2 structures are now established for both potassiumand rubidium-doped polyacetylene. X-ray-diffraction and electrochemical data show that undoped and doped phases coexist at low dopant concentrations (&0.06 K atom per C). X-ray-diffraction data, down to a Bragg spacing of 1.3 A, for polyacetylene heavily doped with potassium (0.125-0.167 K atom per C) is fully consistent with our previously proposed stage-1 tetragonal unit cell containing two polyacetylene chains per alkali-metal column. There is no evidence for our samples requiring a distortion to a monoclinic unit cell as reported by others for heavily doped samples. The nature of structural transformations and the relationship between structure and electronic properties are discussed for potassium-doped polyacetylene.
Synthetic Metals, Sep 1, 1985
Alkali metal-doped polyacetylene exhibits higher thermal stability than either the parent polymer... more Alkali metal-doped polyacetylene exhibits higher thermal stability than either the parent polymer or acceptor-doped complexes. For the Na, K, Rb and Cs complexes in which a channel structure is indicated, this stability appears to be related to the packing arrangement, which interferes with interchain reactions. In contrast with the case for acceptor doping, the conductivities of the alkali metal-doped c/s-polyacetylenes are lower than for correspondingly doped trans-polyacetylenes. However, thermal annealing of the K-doped or Rb-doped polyacetylene (obtained using the naphthalide in THF) results in dramatic enhancement of conductivity for the doped c/s-polymer, but not for the doped trans-polymer. After about a six-fold increase in room-temperature conductivity, the conductivity of K-doped polyacetylene is stable for many hours at 200 °C. C/s-polyacetylene films doped in the same way with other alkali metals do not show this enhancement. Significant changes in unit cell parameters, ESR linewidths, electrical" anisotropy and contact resistance also occur during the annealing of K-doped c/s-polyacetylene. Results presented suggest that thermal annealing of the K-doped polyacetylene eliminates residual conformational defects in partially chemically-isomerized polymer chains, thereby increasing crystalline perfection, increasing the effective conjugation length and increasing the hybridization of alkali metal and carbon orbitals. These changes probably result in the observed conductivity enhancement, the dramatic increase in ESR linewidth (6-12 G to 40-60 G) and the decrease in unit cell parameter.
Journal of Applied Physics, Oct 1, 1976
Formation thermodynamics is examined for two different types of point defects which interrupt con... more Formation thermodynamics is examined for two different types of point defects which interrupt conjugation in polydiacetylene crystals: bond-alternation and orbital-flip defects. While bond-alternation defects in these polymers are analogous to previously investigated radical pair defects in the polyenes, much lower equilibrium concentrations are expected in the polydiacetylenes than in the polyenes. For polydiacetylenes with small substituent groups or high-energy side-group packing, orbital-flip defects provide a more plausible rationale for explaining observed thermochromism and carrier trapping effects in photoconductivity. During the formation of this type of defect, a π orbital at each of the two neighboring sp2 carbon atoms is rotated by 90°, so that the rotated π orbitals become conjugated with the out-of-plane orbitals neighboring sp carbon atoms. Thereby the system of overlapping π orbitals is interrupted without substantially decreasing the electronic stabilization energy. With an intramolecular strain energy increase of only about 2.6 kcal/mole, the polymer chain can return to lattice register within one monomer unit of the defect center. Since the electronic stabilization energy change is even smaller (about 0.2 kcal/mole), the major contribution to defect formation energy arises from the side-group rotations.
Applied Physics Letters, Jan 19, 2009
This work establishes an innovative electrochemical approach to the template-free growth of condu... more This work establishes an innovative electrochemical approach to the template-free growth of conducting polypyrrole and polythiophene wires along predictable interelectrode paths up to 30 m in length. These wires have knobby structures with diameters as small as 98 nm. The conductivity of the polypyrrole wires is 0.5Ϯ 0.3 S cm −1 ; that of the polythiophene wires is 7.6Ϯ 0.8 S cm −1. Controlling the growth path enables fabrication of electrode-wire-target assemblies where the target is a biological cell in the interelectrode gap. Such assemblies are of potential use in cell stimulation studies.
Journal of Chemical Physics, Dec 15, 1982
The energetic degeneracy of the phase-shifted trans polyacetylene chain segments on opposite side... more The energetic degeneracy of the phase-shifted trans polyacetylene chain segments on opposite sides of a soliton center is removed by interchain interactions, which are shown to have important consequences for soliton physics. This energy difference (ESL), the solition-lattice energy, has been calculated from available structural data as a sum of atom-centered, bond-centered, and electrostatic contributions. While ESL is small per C2H2 length of phase-shifted chain (roughly 4 cal/mol for P21/n and 14 cal/mol for P21/a), the resultant total energy cannot generally be ignored since it diverges with increasing separation between soliton and antisoliton or between soliton and chain segment end. Consequences of the interchain interactions are major changes in the equilibrium concentration of soliton pairs, localization of solitons in the proximity of a stationary defect which shifts bond alternation (for chains much longer than the soliton width), and a predicted temperature dependence of phase coherence in bond alternation. Analysis of experimental data provides upper limit estimates for the average chain conjugation length and a lower limit estimate for ESL (greater than 3 cal/mol), which is consistent with the energy calculations based on intermolecular potentials.
Advanced Materials, Apr 7, 2005
Page 1. [18] a) JL Kim, JK Kim, HN Cho, DY Kim, CY Kim, SI Hong, Macromolecules 2000, 33, 5880. b... more Page 1. [18] a) JL Kim, JK Kim, HN Cho, DY Kim, CY Kim, SI Hong, Macromolecules 2000, 33, 5880. b) XW Zhan, YQ Liu, X. Wu, SA Wang, DB Zhu, Macromolecules 2002, 35, 2529. c) CJ Ton-zola, MM Alam, BA Bean, SA Jenekhe, Macromolecules 2004, 37, 3554. ...
Journal of macromolecular science, 1988
ABSTRACT
Mechanical energy harvesters are needed for such diverse applications as self-powered wireless se... more Mechanical energy harvesters are needed for such diverse applications as self-powered wireless sensors, structural and human health monitoring systems, and cheaply harvesting energy from ocean waves. The here reported nanofiber yarn harvesters can electrochemically convert tensile or torsional mechanical energy into electrical energy. Stretching coiled yarns generated 250 W/kg of peak electrical power when cycled up to 30 Hz, and up to 41.2 J/kg of electrical energy per mechanical cycle, when normalized to the weight of the harvester yarn. Unlike for other harvesters, torsional rotation produces both tensile and torsional energy harvesting and no bias voltage is required, even when electrochemically operating in salt water. Since homochiral and heterochiral coiled harvester yarns provide oppositely directed potential changes when stretched, both contribute to output power in a dual-electrode yarn. These energy harvesters were used in the ocean to harvest wave energy, combined with thermally-driven artificial muscles to convert temperature fluctuations to electrical energy, sewn into textiles for use as self-powered respiration sensors, and used to power a LED and to charge a storage capacitor. The development of "piezoelectrochemical spectroscopy" and insights into the hierarchical origins of capacitance increased fundamental understanding. When run in the reverse direction, these muscle types can provide powerful artificial muscles, and the same fibers used as harvesters and muscles can be used to store electrical energy.
Energy Storage Materials, Nov 1, 2019
Building supercapacitors that can provide high energy density over a wide range of temperatures, ... more Building supercapacitors that can provide high energy density over a wide range of temperatures, where traditional energy storage devices fail to operate, requires tailoring of electrolyte and/or electrode material. Here, we show that record gravimetric capacitances of 164 and 182 F g-1 can be attained at-100 and 60 °C, respectively, nearly equivalent to the room-temperature value of 177 F g-1 , when activated carbon-based electrodes with predominantly slit-shaped micropores and a low freezing-point electrolyte are used. Experimental data and density functional theory calculations suggest that electrode material characteristics, such as pore size and shape, matched with the effective size of partially solvated ions of the electrolyte, are the key factors in achieving such performance. This study provides evidence for the effective design of robust supercapacitors with sustained performance at both low and high temperatures.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), 1993
The high cost of powerful, large-stroke, high-stress artificial muscle fibers and wires has combi... more The high cost of powerful, large-stroke, high-stress artificial muscle fibers and wires has combined with typical performance problems, like low-cycle-life under high load, hysteretic behavior, and low efficiencies, to restrict applications. We here demonstrate that inexpensive, high-strength polymer fibers used for fishing line and sewing thread can be easily transformed by non-conventional, extreme twist-insertion processes to provide fast, long-life tensile and torsional muscles that contract by over 49% and lift 100 times heavier loads than the same length and weight natural muscle. These muscles, which are normally thermally actuated, can be powered electrically using sub-volt voltages, photonically, chemically, or by harvesting chemical or thermal energy to provide over 2 times higher specific work than competing nickel-titanium actuator wires. A single muscle fiber weighing 600 mg, made by coiling an 860 μm diameter nylon fishing line, can reversibly lift a kilogram weight 3 cm, and accomplish this once per second when powered by a 75°C temperature change. By weaving or braiding these fibers, we demonstrate textiles that open and close in response to temperature, which might lead to clothing that changes porosity to provide protection and comfort. Use of these muscles for harvesting thermal energy and for window shutters that help conserve energy is demonstrated
Bulletin of the American Physical Society, Mar 5, 2015
Springer eBooks, 1979
In the past decade, anisotropic molecular conductors have been found which possess unusual electr... more In the past decade, anisotropic molecular conductors have been found which possess unusual electrical, optical, magnetic, and, in some cases, mechanical properties. Exploitation of these properties for specific devices is inevitable, and a number of diverse applications of molecular metals have been reported over the past few years. Specifically, these materials have found use as components in batteries, electrolytic capacitors, thermistors, electrochromic displays, optical printing techniques, electrophotography, as electrodes, antistatic coatings, etc. A mora critical and detailed review of the state of the art in this area is given in a paper by Dr. Yoshimura at this NATO-ARI. The scope of this study group is to evaluate the status of applications, to indicate problem areas, and to identify some fruitful directions for future work. But, it must be kept in mind that this is a young field where potential applications are still in a very early stage of development. Consequently, a certain amount of speculation and generalization is unavoidable.
MRS Proceedings, 2001
Reversible actuation strains in excess of 2% in the sheet direction and over 300% in the thicknes... more Reversible actuation strains in excess of 2% in the sheet direction and over 300% in the thickness direction have been produced by single wall carbon nanotube mats when electrochemically charged to +1.5V (vs. SCE) in aqueous sodium chloride solution. The observed strains represent a tenfold increase over that previously reported for carbon nanotube actuators, and is considerably larger than that achievable with polymer ferroelectric actuators. The enhanced actuator strains result from a new mechanism of electrochemically induced "pnuematic actuation" where high pressure gas forms within the porous structure of the nanotube mat causing partial delamination and swelling. An erasable "memory" effect was also observed for pneumatic actuation driven by hydrogen gas evolution/storage in the nanotube electrodes.
Advanced Energy Materials, Mar 1, 2016
Journal of Composite Materials, Nov 29, 2022
This overview focuses on our teams work on using twisted yarns and highly elastic coiled yarns fo... more This overview focuses on our teams work on using twisted yarns and highly elastic coiled yarns for artificial muscles, energy harvesting, energy storage, sensing, and refrigeration. Despite the diversity of these applications for coiled carbon nanotube and polymer yarns, similar fabrication methods are applicable and conversion of coiling twist to yarn twist results in yarn elasticity, actuation, twistocaloric cooling, and the capacitance changes used for energy harvesting and sensing. Likewise, the same biscrolling method yields coiled yarns containing up to 95 weight percent of guest powders that provide various new properties. The obtained performance of the coiled polymer and carbon nanotube yarns are remarkable, such as artificial muscles that generate up to 98 times the output mechanical power than the maximum for the same weight human muscle and mechanical energy harvesters providing a higher peak electrical power per weight than prior art material-based mechanical energy harvesters for stretch frequencies between a few Hz and 600 Hz.
arXiv (Cornell University), Jan 18, 2019
Journal of Applied Physics, Mar 31, 2004
Nanotube sheets, or ''bucky papers,'' have been proposed for use in actuating, structural and ele... more Nanotube sheets, or ''bucky papers,'' have been proposed for use in actuating, structural and electrochemical systems, based in part on their potential mechanical properties. Here, we present results of detailed simulations of networks of nanotubes/ropes, with special emphasis on the effect of joint morphology. We perform detailed simulations of three-dimensional joint deformation, and use the results to inform simulations of two-dimensional ͑2D͒ networks with intertube connections represented by torsion springs. Upper bounds are established on moduli of nanotube sheets, using the 2D Euler beam-network simulations. Comparisons of experimental and simulated response for HiPco-nanotube and laser-ablated nanotube sheets, indicate that ϳ2-30-fold increases in moduli may be achievable in these materials. Increasing the numbers of interrope connections appears to be the best target for improving nanotube sheet stiffnesses in materials containing straight segments.
Physical review, Feb 15, 1990
Structural models for a stage-2 complex are proposed for polyacetylene doped with less than about... more Structural models for a stage-2 complex are proposed for polyacetylene doped with less than about 0.1 potassium or rubidium atoms per carbon. These structures utilize as a basic motif an alkali-metal column surrounded by four planar-zigzag polyacetylene chains, a structure found at the highest dopant levels. In the new stage-2 structures, each polyacetylene chain neighbors only one alkali-metal column, so the phase contains four polymer chains per alkali-metal column. Basic structural aspects for stage-1 and stage-2 structures are now established for both potassiumand rubidium-doped polyacetylene. X-ray-diffraction and electrochemical data show that undoped and doped phases coexist at low dopant concentrations (&0.06 K atom per C). X-ray-diffraction data, down to a Bragg spacing of 1.3 A, for polyacetylene heavily doped with potassium (0.125-0.167 K atom per C) is fully consistent with our previously proposed stage-1 tetragonal unit cell containing two polyacetylene chains per alkali-metal column. There is no evidence for our samples requiring a distortion to a monoclinic unit cell as reported by others for heavily doped samples. The nature of structural transformations and the relationship between structure and electronic properties are discussed for potassium-doped polyacetylene.
Synthetic Metals, Sep 1, 1985
Alkali metal-doped polyacetylene exhibits higher thermal stability than either the parent polymer... more Alkali metal-doped polyacetylene exhibits higher thermal stability than either the parent polymer or acceptor-doped complexes. For the Na, K, Rb and Cs complexes in which a channel structure is indicated, this stability appears to be related to the packing arrangement, which interferes with interchain reactions. In contrast with the case for acceptor doping, the conductivities of the alkali metal-doped c/s-polyacetylenes are lower than for correspondingly doped trans-polyacetylenes. However, thermal annealing of the K-doped or Rb-doped polyacetylene (obtained using the naphthalide in THF) results in dramatic enhancement of conductivity for the doped c/s-polymer, but not for the doped trans-polymer. After about a six-fold increase in room-temperature conductivity, the conductivity of K-doped polyacetylene is stable for many hours at 200 °C. C/s-polyacetylene films doped in the same way with other alkali metals do not show this enhancement. Significant changes in unit cell parameters, ESR linewidths, electrical" anisotropy and contact resistance also occur during the annealing of K-doped c/s-polyacetylene. Results presented suggest that thermal annealing of the K-doped polyacetylene eliminates residual conformational defects in partially chemically-isomerized polymer chains, thereby increasing crystalline perfection, increasing the effective conjugation length and increasing the hybridization of alkali metal and carbon orbitals. These changes probably result in the observed conductivity enhancement, the dramatic increase in ESR linewidth (6-12 G to 40-60 G) and the decrease in unit cell parameter.
Journal of Applied Physics, Oct 1, 1976
Formation thermodynamics is examined for two different types of point defects which interrupt con... more Formation thermodynamics is examined for two different types of point defects which interrupt conjugation in polydiacetylene crystals: bond-alternation and orbital-flip defects. While bond-alternation defects in these polymers are analogous to previously investigated radical pair defects in the polyenes, much lower equilibrium concentrations are expected in the polydiacetylenes than in the polyenes. For polydiacetylenes with small substituent groups or high-energy side-group packing, orbital-flip defects provide a more plausible rationale for explaining observed thermochromism and carrier trapping effects in photoconductivity. During the formation of this type of defect, a π orbital at each of the two neighboring sp2 carbon atoms is rotated by 90°, so that the rotated π orbitals become conjugated with the out-of-plane orbitals neighboring sp carbon atoms. Thereby the system of overlapping π orbitals is interrupted without substantially decreasing the electronic stabilization energy. With an intramolecular strain energy increase of only about 2.6 kcal/mole, the polymer chain can return to lattice register within one monomer unit of the defect center. Since the electronic stabilization energy change is even smaller (about 0.2 kcal/mole), the major contribution to defect formation energy arises from the side-group rotations.
Applied Physics Letters, Jan 19, 2009
This work establishes an innovative electrochemical approach to the template-free growth of condu... more This work establishes an innovative electrochemical approach to the template-free growth of conducting polypyrrole and polythiophene wires along predictable interelectrode paths up to 30 m in length. These wires have knobby structures with diameters as small as 98 nm. The conductivity of the polypyrrole wires is 0.5Ϯ 0.3 S cm −1 ; that of the polythiophene wires is 7.6Ϯ 0.8 S cm −1. Controlling the growth path enables fabrication of electrode-wire-target assemblies where the target is a biological cell in the interelectrode gap. Such assemblies are of potential use in cell stimulation studies.
Journal of Chemical Physics, Dec 15, 1982
The energetic degeneracy of the phase-shifted trans polyacetylene chain segments on opposite side... more The energetic degeneracy of the phase-shifted trans polyacetylene chain segments on opposite sides of a soliton center is removed by interchain interactions, which are shown to have important consequences for soliton physics. This energy difference (ESL), the solition-lattice energy, has been calculated from available structural data as a sum of atom-centered, bond-centered, and electrostatic contributions. While ESL is small per C2H2 length of phase-shifted chain (roughly 4 cal/mol for P21/n and 14 cal/mol for P21/a), the resultant total energy cannot generally be ignored since it diverges with increasing separation between soliton and antisoliton or between soliton and chain segment end. Consequences of the interchain interactions are major changes in the equilibrium concentration of soliton pairs, localization of solitons in the proximity of a stationary defect which shifts bond alternation (for chains much longer than the soliton width), and a predicted temperature dependence of phase coherence in bond alternation. Analysis of experimental data provides upper limit estimates for the average chain conjugation length and a lower limit estimate for ESL (greater than 3 cal/mol), which is consistent with the energy calculations based on intermolecular potentials.
Advanced Materials, Apr 7, 2005
Page 1. [18] a) JL Kim, JK Kim, HN Cho, DY Kim, CY Kim, SI Hong, Macromolecules 2000, 33, 5880. b... more Page 1. [18] a) JL Kim, JK Kim, HN Cho, DY Kim, CY Kim, SI Hong, Macromolecules 2000, 33, 5880. b) XW Zhan, YQ Liu, X. Wu, SA Wang, DB Zhu, Macromolecules 2002, 35, 2529. c) CJ Ton-zola, MM Alam, BA Bean, SA Jenekhe, Macromolecules 2004, 37, 3554. ...
Journal of macromolecular science, 1988
ABSTRACT
Mechanical energy harvesters are needed for such diverse applications as self-powered wireless se... more Mechanical energy harvesters are needed for such diverse applications as self-powered wireless sensors, structural and human health monitoring systems, and cheaply harvesting energy from ocean waves. The here reported nanofiber yarn harvesters can electrochemically convert tensile or torsional mechanical energy into electrical energy. Stretching coiled yarns generated 250 W/kg of peak electrical power when cycled up to 30 Hz, and up to 41.2 J/kg of electrical energy per mechanical cycle, when normalized to the weight of the harvester yarn. Unlike for other harvesters, torsional rotation produces both tensile and torsional energy harvesting and no bias voltage is required, even when electrochemically operating in salt water. Since homochiral and heterochiral coiled harvester yarns provide oppositely directed potential changes when stretched, both contribute to output power in a dual-electrode yarn. These energy harvesters were used in the ocean to harvest wave energy, combined with thermally-driven artificial muscles to convert temperature fluctuations to electrical energy, sewn into textiles for use as self-powered respiration sensors, and used to power a LED and to charge a storage capacitor. The development of "piezoelectrochemical spectroscopy" and insights into the hierarchical origins of capacitance increased fundamental understanding. When run in the reverse direction, these muscle types can provide powerful artificial muscles, and the same fibers used as harvesters and muscles can be used to store electrical energy.
Energy Storage Materials, Nov 1, 2019
Building supercapacitors that can provide high energy density over a wide range of temperatures, ... more Building supercapacitors that can provide high energy density over a wide range of temperatures, where traditional energy storage devices fail to operate, requires tailoring of electrolyte and/or electrode material. Here, we show that record gravimetric capacitances of 164 and 182 F g-1 can be attained at-100 and 60 °C, respectively, nearly equivalent to the room-temperature value of 177 F g-1 , when activated carbon-based electrodes with predominantly slit-shaped micropores and a low freezing-point electrolyte are used. Experimental data and density functional theory calculations suggest that electrode material characteristics, such as pore size and shape, matched with the effective size of partially solvated ions of the electrolyte, are the key factors in achieving such performance. This study provides evidence for the effective design of robust supercapacitors with sustained performance at both low and high temperatures.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), 1993
The high cost of powerful, large-stroke, high-stress artificial muscle fibers and wires has combi... more The high cost of powerful, large-stroke, high-stress artificial muscle fibers and wires has combined with typical performance problems, like low-cycle-life under high load, hysteretic behavior, and low efficiencies, to restrict applications. We here demonstrate that inexpensive, high-strength polymer fibers used for fishing line and sewing thread can be easily transformed by non-conventional, extreme twist-insertion processes to provide fast, long-life tensile and torsional muscles that contract by over 49% and lift 100 times heavier loads than the same length and weight natural muscle. These muscles, which are normally thermally actuated, can be powered electrically using sub-volt voltages, photonically, chemically, or by harvesting chemical or thermal energy to provide over 2 times higher specific work than competing nickel-titanium actuator wires. A single muscle fiber weighing 600 mg, made by coiling an 860 μm diameter nylon fishing line, can reversibly lift a kilogram weight 3 cm, and accomplish this once per second when powered by a 75°C temperature change. By weaving or braiding these fibers, we demonstrate textiles that open and close in response to temperature, which might lead to clothing that changes porosity to provide protection and comfort. Use of these muscles for harvesting thermal energy and for window shutters that help conserve energy is demonstrated
Bulletin of the American Physical Society, Mar 5, 2015
Springer eBooks, 1979
In the past decade, anisotropic molecular conductors have been found which possess unusual electr... more In the past decade, anisotropic molecular conductors have been found which possess unusual electrical, optical, magnetic, and, in some cases, mechanical properties. Exploitation of these properties for specific devices is inevitable, and a number of diverse applications of molecular metals have been reported over the past few years. Specifically, these materials have found use as components in batteries, electrolytic capacitors, thermistors, electrochromic displays, optical printing techniques, electrophotography, as electrodes, antistatic coatings, etc. A mora critical and detailed review of the state of the art in this area is given in a paper by Dr. Yoshimura at this NATO-ARI. The scope of this study group is to evaluate the status of applications, to indicate problem areas, and to identify some fruitful directions for future work. But, it must be kept in mind that this is a young field where potential applications are still in a very early stage of development. Consequently, a certain amount of speculation and generalization is unavoidable.
MRS Proceedings, 2001
Reversible actuation strains in excess of 2% in the sheet direction and over 300% in the thicknes... more Reversible actuation strains in excess of 2% in the sheet direction and over 300% in the thickness direction have been produced by single wall carbon nanotube mats when electrochemically charged to +1.5V (vs. SCE) in aqueous sodium chloride solution. The observed strains represent a tenfold increase over that previously reported for carbon nanotube actuators, and is considerably larger than that achievable with polymer ferroelectric actuators. The enhanced actuator strains result from a new mechanism of electrochemically induced "pnuematic actuation" where high pressure gas forms within the porous structure of the nanotube mat causing partial delamination and swelling. An erasable "memory" effect was also observed for pneumatic actuation driven by hydrogen gas evolution/storage in the nanotube electrodes.
Advanced Energy Materials, Mar 1, 2016
Journal of Composite Materials, Nov 29, 2022
This overview focuses on our teams work on using twisted yarns and highly elastic coiled yarns fo... more This overview focuses on our teams work on using twisted yarns and highly elastic coiled yarns for artificial muscles, energy harvesting, energy storage, sensing, and refrigeration. Despite the diversity of these applications for coiled carbon nanotube and polymer yarns, similar fabrication methods are applicable and conversion of coiling twist to yarn twist results in yarn elasticity, actuation, twistocaloric cooling, and the capacitance changes used for energy harvesting and sensing. Likewise, the same biscrolling method yields coiled yarns containing up to 95 weight percent of guest powders that provide various new properties. The obtained performance of the coiled polymer and carbon nanotube yarns are remarkable, such as artificial muscles that generate up to 98 times the output mechanical power than the maximum for the same weight human muscle and mechanical energy harvesters providing a higher peak electrical power per weight than prior art material-based mechanical energy harvesters for stretch frequencies between a few Hz and 600 Hz.