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Liao W, Yang Z. 3D printing programmable liquid crystal elastomer soft pneumatic actuators. MATERIALS HORIZONS 2023; 10:576-584. [PMID: 36468657 DOI: 10.1039/d2mh01001a] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Soft pneumatic actuators (SPAs) rely on anisotropic mechanical properties to generate specific motions after inflation. To achieve mechanical anisotropy, additional stiff materials or heterogeneous structures are typically introduced in isotropic base materials. However, the inherent limitations of these strategies may lead to potential interfacial problems or inefficient material usage. Herein, we develop a new strategy for fabricating SPAs based on an aligned liquid crystal elastomer (LCE) by a modified 3D printing technology. A rotating substrate enables the one-step fabrication of tubular LCE-SPAs with designed alignments in three dimensions. The alignment can be precisely programmed through printing, resulting in intrinsic mechanical anisotropy of the LCE. With a specially designed alignment, LCE-SPAs can achieve basic motions-contraction, elongation, bending, and twisting-and accomplish diverse tasks, e.g., grabbing objects and mixing water. This study provides a new perspective for the design and fabrication of SPAs.
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Affiliation(s)
- Wei Liao
- Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, China.
| | - Zhongqiang Yang
- Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, China.
- Laboratory of Flexible Electronics Technology, Tsinghua University, Beijing, China
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2
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Johnson KJ, Wiegart L, Abbott AC, Johnson EB, Baur JW, Koerner H. In Operando Monitoring of Dynamic Recovery in 3D-Printed Thermoset Nanocomposites by XPCS. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:8758-8768. [PMID: 31244252 DOI: 10.1021/acs.langmuir.9b00766] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Extrusion-based additive manufacturing methods, such as direct-write of carbon fiber-reinforced epoxy inks, have become an attractive route toward development of structural composites in recent years, because of emerging techniques such as big area additive manufacturing. The development of improved materials for these methods has been a major focus area; however, an understanding of the effects of the printing process on the structural and dynamic recovery in printed materials remains largely unexplored. The goal of this work is to capture multiscale and temporal morphology and dynamics within thermosetting composite inks to determine the parameters during the printing process that influence the recovery of the printed material. Herein, we use X-ray photon correlation spectroscopy in small-angle scattering geometry to reveal both morphology and recovery dynamics of a nanoparticle (layered-silicate Cloisite 30B) in a thermoset epoxy resin (EPON 826) during the printing process in real time. Our results show that the dynamics of the layered silicate particles during recovery are anisotropic and slow down to behavior which is characteristic of aging in colloidal clay suspensions around tage ≈ 12 s. The dynamics and alignment of the particles during recovery were tempo-spatially mapped, and the recovery post printing was shown to be strongly influenced by the deposition onto the build plate in addition to the extrusion through the print head. Our in operando results provide insight into the parameters that must be considered when optimizing materials and methods for precisely tailored local properties during 3D printing.
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Affiliation(s)
- Kyle J Johnson
- Air Force Research Laboratory, Materials and Manufacturing Directorate , 2941 Hobson Way, Wright-Patterson AFB , Ohio 45433 , United States
| | - Lutz Wiegart
- Brookhaven National Laboratory, Photon Sciences Directorate , 744 Ring Road , Upton , New York 11973 , United States
| | - Andrew C Abbott
- Air Force Research Laboratory, Materials and Manufacturing Directorate , 2941 Hobson Way, Wright-Patterson AFB , Ohio 45433 , United States
| | - Elias B Johnson
- Air Force Research Laboratory, Materials and Manufacturing Directorate , 2941 Hobson Way, Wright-Patterson AFB , Ohio 45433 , United States
| | - Jeffery W Baur
- Air Force Research Laboratory, Materials and Manufacturing Directorate , 2941 Hobson Way, Wright-Patterson AFB , Ohio 45433 , United States
| | - Hilmar Koerner
- Air Force Research Laboratory, Materials and Manufacturing Directorate , 2941 Hobson Way, Wright-Patterson AFB , Ohio 45433 , United States
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Zhao J, Chen P, Lin Y, Chang J, Lu A, Chen W, Meng L, Wang D, Li L. Stretch-Induced Crystallization and Phase Transitions of Poly(dimethylsiloxane) at Low Temperatures: An in Situ Synchrotron Radiation Wide-Angle X-ray Scattering Study. Macromolecules 2018. [DOI: 10.1021/acs.macromol.8b01872] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Jingyun Zhao
- National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, China
- Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621900, China
| | - Pinzhang Chen
- National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, China
| | - Yuanfei Lin
- National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, China
| | - Jiarui Chang
- National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, China
| | - Ai Lu
- Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621900, China
| | - Wei Chen
- National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, China
| | - Lingpu Meng
- National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, China
| | - Daoliang Wang
- National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, China
| | - Liangbin Li
- National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, China
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Study on Phase Transformation Behavior of Strain-induced PLLA Mesophase by Polarized Infrared Spectroscopy. CHINESE JOURNAL OF POLYMER SCIENCE 2018. [DOI: 10.1007/s10118-019-2184-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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5
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Dunkerley E, Schmidt DF. Understanding the Consequences of Intercalation Using Model Polymer Nanolaminates. Macromolecules 2015. [DOI: 10.1021/acs.macromol.5b01788] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Erik Dunkerley
- Department of Plastics Engineering, University of Massachusetts Lowell, 1 University Avenue, Lowell, Massachusetts 01854, United States
| | - Daniel F. Schmidt
- Department of Plastics Engineering, University of Massachusetts Lowell, 1 University Avenue, Lowell, Massachusetts 01854, United States
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Miyazaki T, Takeda Y, Hoshiko A, Shimokita K, Ogomi D. Evaluation of oriented amorphous regions in polymer films during uniaxial deformation; structural characterization of a poly(vinyl alcohol) film during stretching in boric acid aqueous solutions. POLYM ENG SCI 2014. [DOI: 10.1002/pen.23913] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Tsukasa Miyazaki
- Functional Design Technology Center; Nitto Denko Corporation, Shimohozumi, Ibaraki; Osaka 567-8680 Japan
| | - Yuuki Takeda
- Functional Design Technology Center; Nitto Denko Corporation, Shimohozumi, Ibaraki; Osaka 567-8680 Japan
| | - Akie Hoshiko
- Functional Design Technology Center; Nitto Denko Corporation, Shimohozumi, Ibaraki; Osaka 567-8680 Japan
| | - Keisuke Shimokita
- Functional Design Technology Center; Nitto Denko Corporation, Shimohozumi, Ibaraki; Osaka 567-8680 Japan
| | - Daisuke Ogomi
- Information Fine Materials Sector; Research and Development Division, Nitto Denko Corporation, Hongo, Minosatocho; Onomichi Hiroshima 722-0212 Japan
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Domenici V. 2H NMR studies of liquid crystal elastomers: macroscopic vs. molecular properties. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2012; 63:1-32. [PMID: 22546343 DOI: 10.1016/j.pnmrs.2011.07.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 07/27/2011] [Indexed: 05/31/2023]
Affiliation(s)
- Valentina Domenici
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56126 Pisa, Italy.
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Fillery SP, Koerner H, Drummy L, Dunkerley E, Durstock MF, Schmidt DF, Vaia RA. Nanolaminates: increasing dielectric breakdown strength of composites. ACS APPLIED MATERIALS & INTERFACES 2012; 4:1388-96. [PMID: 22301841 DOI: 10.1021/am201650g] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Processable, low-cost, high-performance hybrid dielectrics are enablers for a vast array of green technologies, including high-temperature electrical insulation and pulsed power capacitors for all-electric transportation vehicles. Maximizing the dielectric breakdown field (E(BD)), in conjunction with minimization of leakage current, directly impacts system performance because of the field's quadratic relationship with electrostatic energy storage density. On the basis of the extreme internal interfacial area and ultrafine morphology, polymer-inorganic nanocomposites (PNCs) have demonstrated modest increases in E(BD) at very low inorganic loadings, but because of insufficient control of the hierarchal morphology of the blend, have yielded a precipitous decline in E(BD) at intermediate and high inorganic volume fractions. Here in, we demonstrate that E(BD) can be increased up to these intermediate inorganic volume fractions by creating uniform one-dimensional nanocomposites (nanolaminates) rather than blends of spherical inorganic nanoparticles and polymers. Free standing nanolaminates of highly aligned and dispersed montmorillonite in polyvinyl butyral exhibited enhancements in E(BD) up to 30 vol % inorganic (70 wt % organically modified montmorillonite). These relative enhancements extend up to five times the inorganic fraction observed for random nanoparticle dispersions, and are anywhere from two to four times greater than observed at comparable volume fraction of nanoparticles. The breakdown characteristics of this model system suggested a trade-off between increased path tortuosity and polymer-deficient structural defects. This implies that an idealized PNC morphology to retard the breakdown cascade perpendicular to the electrodes will occur at intermediate volume fractions and resemble a discotic nematic phase where highly aligned, high-aspect ratio nanometer thick plates are uniformly surrounded by nanoscopic regions of polymer.
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Rinaldi RG, Boyce MC, Weigand SJ, Londono DJ, Guise MW. Microstructure evolution during tensile loading histories of a polyurea. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/polb.22352] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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11
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Dunkerley E, Koerner H, Vaia RA, Schmidt D. Structure and dynamic mechanical properties of highly oriented PS/clay nanolaminates over the entire composition range. POLYMER 2011. [DOI: 10.1016/j.polymer.2011.01.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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12
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Koerner H, Kelley J, George J, Drummy L, Mirau P, Bell NS, Hsu JWP, Vaia RA. ZnO Nanorod−Thermoplastic Polyurethane Nanocomposites: Morphology and Shape Memory Performance. Macromolecules 2009. [DOI: 10.1021/ma901671v] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Hilmar Koerner
- Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXBN, 2941 Hobson Way, Wright-Patterson AFB, Ohio 45433
- Universal Technology Corporation, Dayton, Ohio, 45432
| | - John Kelley
- Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXBN, 2941 Hobson Way, Wright-Patterson AFB, Ohio 45433
| | - Justin George
- Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXBN, 2941 Hobson Way, Wright-Patterson AFB, Ohio 45433
| | - Lawrence Drummy
- Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXBN, 2941 Hobson Way, Wright-Patterson AFB, Ohio 45433
| | - Peter Mirau
- Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXBN, 2941 Hobson Way, Wright-Patterson AFB, Ohio 45433
| | - Nelson S. Bell
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico, 87185
| | - Julia W. P. Hsu
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico, 87185
| | - Richard A. Vaia
- Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXBN, 2941 Hobson Way, Wright-Patterson AFB, Ohio 45433
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Shan H. Kinetics Study of Mesophase-Crystal Transformation in Highly Oriented Homogeneous Poly(ethylene- co-1-octene) Filament. INTERNATIONAL JOURNAL OF POLYMER ANALYSIS AND CHARACTERIZATION 2009. [DOI: 10.1080/10236660802657797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Koerner H, Kelley JJ, Vaia RA. Transient Microstructure of Low Hard Segment Thermoplastic Polyurethane under Uniaxial Deformation. Macromolecules 2008. [DOI: 10.1021/ma800306z] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Hilmar Koerner
- Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXBP, 2941 Hobson Way, Wright-Patterson AFB, Ohio 45433, and Universal Technology Corporation, Dayton, Ohio 45432
| | - John J. Kelley
- Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXBP, 2941 Hobson Way, Wright-Patterson AFB, Ohio 45433, and Universal Technology Corporation, Dayton, Ohio 45432
| | - Richard A. Vaia
- Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXBP, 2941 Hobson Way, Wright-Patterson AFB, Ohio 45433, and Universal Technology Corporation, Dayton, Ohio 45432
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15
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Deformation-induced highly oriented and stable mesomorphic phase in quenched isotactic polypropylene. POLYMER 2007. [DOI: 10.1016/j.polymer.2007.08.066] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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16
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Microstructural evolution of electrically activated polypropylene/layered silicate nanocomposites investigated by in situ synchrotron wide-angle X-ray scattering and dielectric relaxation analysis. POLYMER 2006. [DOI: 10.1016/j.polymer.2006.06.029] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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17
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Yoonessi M, Toghiani H, Pittman CU. Orientation of montmorillonite clay in dicyclopentadiene/organically modified clay dispersions and nanocomposites. J Appl Polym Sci 2006. [DOI: 10.1002/app.24387] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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Bhawe DM, Cohen C, Escobedo FA. Effect of chain stiffness and entanglements on the elastic behavior of end-linked elastomers. J Chem Phys 2005; 123:014909. [PMID: 16035871 DOI: 10.1063/1.1949210] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The effect of chain stiffness and entanglements on the elastic behavior and microscopic structure of cross-linked polymer networks was studied using Monte Carlo simulations. We investigated the behavior of entangled and entanglement-free networks at various degrees of chain stiffness and densities. Based on previous results that indicated that trapped entanglements prevent strain-induced order-disorder transitions in semiflexible chain networks, we prepared the entangled networks by end-linking the chains in very dilute conditions so as to minimize the extent of trapped entanglements. We also considered the entanglement-free case by using a "diamond" structure. We found that the presence of even a very small amount of trapped entanglements is enough to prevent a discontinuous strain-induced transition to an ordered phase. In these mildly entangled networks, a nematiclike order is eventually attained at high extensions but the elastic response remains continuous and the cross-links remain uniformly distributed through the simulation box. The entanglement-free diamond networks on the other hand show discontinuities in their stress-strain data. Networks at higher densities exhibit a more stable ordered phase and show an unusual staircaselike stress-strain curve. This is the result of a stepwise extension mechanism in which the chains form ordered domains that exclude the cross-links. Extension is achieved by increasing the number of these ordered domains in the strain direction. Cross-links aggregate in the spaces between these ordered domains and form periodic bands. Each vertical upturn in the stress-strain data corresponds to the existence of an integer number of ordered domains. This stepwise elastic behavior is found to be similar to that exhibited by some tough natural materials.
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Affiliation(s)
- Dhananjay M Bhawe
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA
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Li L, de Jeu WH. Flow-induced mesophases in crystallizable polymers. ADVANCES IN POLYMER SCIENCE 2005. [DOI: 10.1007/b107175] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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Koerner H, Price G, Pearce NA, Alexander M, Vaia RA. Remotely actuated polymer nanocomposites--stress-recovery of carbon-nanotube-filled thermoplastic elastomers. NATURE MATERIALS 2004; 3:115-20. [PMID: 14743213 DOI: 10.1038/nmat1059] [Citation(s) in RCA: 475] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2003] [Accepted: 12/22/2003] [Indexed: 05/19/2023]
Abstract
Stimuli-responsive (active) materials undergo large-scale shape or property changes in response to an external stimulus such as stress, temperature, light or pH. Technological uses range from durable, shape-recovery eye-glass frames, to temperature-sensitive switches, to the generation of stress to induce mechanical motion. Here, we demonstrate that the uniform dispersion of 1-5 vol.% of carbon nanotubes in a thermoplastic elastomer yields nanocomposites that can store and subsequently release, through remote means, up to 50% more recovery stress than the pristine resin. The anisotropic nanotubes increase the rubbery modulus by a factor of 2 to 5 (for 1-5 vol.%) and improve shape fixity by enhancing strain-induced crystallization. Non-radiative decay of infrared photons absorbed by the nanotubes raises the internal temperature, melting strain-induced polymer crystallites (which act as physical crosslinks that secure the deformed shape) and remotely trigger the release of the stored strain energy. Comparable effects occur for electrically induced actuation associated with Joule heating of the matrix when a current is passed through the conductive percolative network of the nanotubes within the resin. This unique combination of properties, directly arising from the nanocomposite morphology, demonstrates new opportunities for the design and fabrication of stimuli-responsive polymers, which are otherwise not available in one material system.
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Affiliation(s)
- Hilmar Koerner
- Nonmetallic Materials Division, University of Dayton Research Institute, 300 College Park Ave, Dayton, Ohio 45469, USA
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Batra A, Hedden RC, Schofield P, Barnes A, Cohen C, Duncan TM. Conformational Behavior of Guest Chains in Uniaxially Stretched Poly(diethylsiloxane) Elastomers: 2H NMR and SANS. Macromolecules 2003. [DOI: 10.1021/ma035143v] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ashish Batra
- School of Chemical and Biomolecular Engineering, Olin Hall, Cornell University, Ithaca, New York 14853, Evergreen State College, Olympia, Washington 98505, and Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
| | - Ronald C. Hedden
- School of Chemical and Biomolecular Engineering, Olin Hall, Cornell University, Ithaca, New York 14853, Evergreen State College, Olympia, Washington 98505, and Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
| | - Paula Schofield
- School of Chemical and Biomolecular Engineering, Olin Hall, Cornell University, Ithaca, New York 14853, Evergreen State College, Olympia, Washington 98505, and Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
| | - Aaron Barnes
- School of Chemical and Biomolecular Engineering, Olin Hall, Cornell University, Ithaca, New York 14853, Evergreen State College, Olympia, Washington 98505, and Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
| | - Claude Cohen
- School of Chemical and Biomolecular Engineering, Olin Hall, Cornell University, Ithaca, New York 14853, Evergreen State College, Olympia, Washington 98505, and Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
| | - T. M. Duncan
- School of Chemical and Biomolecular Engineering, Olin Hall, Cornell University, Ithaca, New York 14853, Evergreen State College, Olympia, Washington 98505, and Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
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