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Bagheri R, Ball AK, Kasraie M, Chandra A, Chen X, Miskioglu I, Shan Z, Pour Shahid Saeed Abadi P. Conductive 3D nano-biohybrid systems based on densified carbon nanotube forests and living cells. JOURNAL OF MATERIALS RESEARCH 2023; 39:137-149. [PMID: 38223564 PMCID: PMC10784361 DOI: 10.1557/s43578-023-01163-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Accepted: 09/08/2023] [Indexed: 01/16/2024]
Abstract
Conductive biohybrid cell-material systems have applications in bioelectronics and biorobotics. To date, conductive scaffolds are limited to those with low electrical conductivity or 2D sheets. Here, 3D biohybrid conductive systems are developed using fibroblasts or cardiomyocytes integrated with carbon nanotube (CNT) forests that are densified due to interactions with a gelatin coating. CNT forest scaffolds with a height range of 120-240 µm and an average electrical conductivity of 0.6 S/cm are developed and shown to be cytocompatible as evidenced from greater than 89% viability measured by live-dead assay on both cells on day 1. The cells spread on top and along the height of the CNT forest scaffolds. Finally, the scaffolds have no adverse effects on the expression of genes related to cardiomyocyte maturation and functionality, or fibroblast migration, adhesion, and spreading. The results show that the scaffold could be used in applications ranging from organ-on-a-chip systems to muscle actuators. Graphical abstract
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Affiliation(s)
- Roya Bagheri
- Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, MI 49931 USA
- Health Research Institute, Michigan Technological University, Houghton, MI 49931 USA
| | - Alicia K. Ball
- Chemical Engineering, Michigan Technological University, Houghton, MI 49931 USA
| | - Masoud Kasraie
- Materials Science and Engineering, Michigan Technological University, Houghton, MI 49931 USA
| | - Aparna Chandra
- Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, MI 49931 USA
| | - Xinqian Chen
- Health Research Institute, Michigan Technological University, Houghton, MI 49931 USA
- Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, MI 49931 USA
| | - Ibrahim Miskioglu
- Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, MI 49931 USA
| | - Zhiying Shan
- Health Research Institute, Michigan Technological University, Houghton, MI 49931 USA
- Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, MI 49931 USA
- Biomedical Engineering, Michigan Technological University, Houghton, MI 49931 USA
| | - Parisa Pour Shahid Saeed Abadi
- Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, MI 49931 USA
- Health Research Institute, Michigan Technological University, Houghton, MI 49931 USA
- Materials Science and Engineering, Michigan Technological University, Houghton, MI 49931 USA
- Biomedical Engineering, Michigan Technological University, Houghton, MI 49931 USA
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Bellott E, Li Y, Gunter C, Kovaleski S, Maschmann MR. Investigating the Electromechanical Sensitivity of Carbon-Nanotube-Coated Microfibers. SENSORS (BASEL, SWITZERLAND) 2023; 23:s23115190. [PMID: 37299915 DOI: 10.3390/s23115190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Revised: 05/25/2023] [Accepted: 05/26/2023] [Indexed: 06/12/2023]
Abstract
The piezoresistance of carbon nanotube (CNT)-coated microfibers is examined using diametric compression. Diverse CNT forest morphologies were studied by changing the CNT length, diameter, and areal density via synthesis time and fiber surface treatment prior to CNT synthesis. Large-diameter (30-60 nm) and relatively low-density CNTs were synthesized on as-received glass fibers. Small-diameter (5-30 nm) and-high density CNTs were synthesized on glass fibers coated with 10 nm of alumina. The CNT length was controlled by adjusting synthesis time. Electromechanical compression was performed by measuring the electrical resistance in the axial direction during diametric compression. Gauge factors exceeding three were measured for small-diameter (<25 μm) coated fibers, corresponding to as much as 35% resistance change per micrometer of compression. The gauge factor for high-density, small-diameter CNT forests was generally greater than those for low-density, large-diameter forests. A finite element simulation shows that the piezoresistive response originates from both the contact resistance and intrinsic resistance of the forest itself. The change in contact and intrinsic resistance are balanced for relatively short CNT forests, while the response is dominated by CNT electrode contact resistance for taller CNT forests. These results are expected to guide the design of piezoresistive flow and tactile sensors.
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Affiliation(s)
- Elizabeth Bellott
- Department of Mechanical & Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA
| | - Yushan Li
- Department of Mechanical & Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA
| | - Connor Gunter
- Department of Electrical Engineering & Computer Science, University of Missouri, Columbia, MO 65211, USA
| | - Scott Kovaleski
- Department of Electrical Engineering & Computer Science, University of Missouri, Columbia, MO 65211, USA
| | - Matthew R Maschmann
- Department of Mechanical & Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA
- MU Materials Science and Engineering Institute, University of Missouri, Columbia, MO 65211, USA
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Morco SR, Jensen BD, Bowden AE. Curvature-induced defects on carbon-infiltrated carbon nanotube forests. RSC Adv 2022; 12:2115-2122. [PMID: 35425237 PMCID: PMC8979125 DOI: 10.1039/d1ra07243a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 01/05/2022] [Indexed: 12/21/2022] Open
Abstract
A morphological study of the micro-scale defects induced by growing a carbon-infiltrated carbon nanotube (CICNT) forest on concave substrates was conducted. Two CICNT heights (roughly 60 μm and 400 μm) and 4 curvatures (1–4 mm ID) were studied in order to test the geometric limitations. Defects were categorized and quantified by scanning electron microscopy (SEM) of the tops and cross-sections. These deformities were categorized as increased roughness on the top surface, a corrugated (also called wavy or rippled) forest, a curved forest, an inside crevice where the forest separates, and increased forest density on the top surface. Roughness increased nearly 3-fold with the taller forest heights no matter the substrate curvature. Due to the geometric limitations of CICNT height and substrate curvature, all other microscale defects were significantly more present on samples with a small radius of curvature and a tall CICNT forest (p < 0.05). These buckling and warping types of defects were attributed to the increase in circumferential compression as the forest grows as well as the van der Waals interactions between the nanotubes. Because the fabrication process for CICNT involves growing a CNT forest and then infiltrating it with pyrolytic carbon, this work may be applicable to other CNT forests on concave substrates within these forest heights and substrate curvatures. A morphological study of the micro-scale defects induced by growing a carbon-infiltrated carbon nanotube (CICNT) forest on concave substrates was conducted.![]()
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Affiliation(s)
- Stephanie R Morco
- Brigham Young University, Department of Mechanical Engineering 350 Engineering Building Provo UT 84602 USA
| | - Brian D Jensen
- Brigham Young University, Department of Mechanical Engineering 350 Engineering Building Provo UT 84602 USA
| | - Anton E Bowden
- Brigham Young University, Department of Mechanical Engineering 350 Engineering Building Provo UT 84602 USA
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Kaiser AL, Lidston DL, Peterson SC, Acauan LH, Steiner SA, Guzman de Villoria R, Vanderhout AR, Stein IY, Wardle BL. Substrate adhesion evolves non-monotonically with processing time in millimeter-scale aligned carbon nanotube arrays. NANOSCALE 2021; 13:261-271. [PMID: 33331843 DOI: 10.1039/d0nr05469k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The advantageous intrinsic and scale-dependent properties of aligned nanofibers (NFs) and their assembly into 3D architectures motivate their use as dry adhesives and shape-engineerable materials. While controlling NF-substrate adhesion is critical for scaled manufacturing and application-specific performance, current understanding of how this property evolves with processing conditions is limited. In this report, we introduce substrate adhesion predictive capabilities by using an exemplary array of NFs, aligned carbon nanotubes (CNTs), studied as a function of their processing. Substrate adhesion is found to scale non-monotonically with process time in a hydrocarbon environment and is investigated via the tensile pull-off of mm-scale CNT arrays from their growth substrate. CNT synthesis follows two regimes: Mode I ('Growth') and Mode II ('Post-Growth'), separated by growth termination. Within 10 minutes of post-growth, experiments and modeling indicate an order-of-magnitude increase in CNT array-substrate adhesion strength (∼40 to 285 kPa) and effective elastic array modulus (∼6 to 47 MPa), and a two-orders-of-magnitude increase in the single CNT-substrate adhesion force (∼0.190 to 12.3 nN) and work of adhesion (∼0.07 to 1.5 J m-2), where the iron catalyst is found to remain on the substrate. Growth number decay in Mode I and carbon accumulation in Mode II contribute to the mechanical response, which may imply a change in the deformation mechanism. Predictive capabilities of the model are assessed for previously studied NF arrays, suggesting that the current framework can enable the future design and manufacture of high-value NF array applications.
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Affiliation(s)
- Ashley L Kaiser
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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Mirza Gheitaghy A, Poelma RH, Sacco L, Vollebregt S, Zhang GQ. Vertically-Aligned Multi-Walled Carbon Nano Tube Pillars with Various Diameters under Compression: Pristine and NbTiN Coated. NANOMATERIALS 2020; 10:nano10061189. [PMID: 32570835 PMCID: PMC7353429 DOI: 10.3390/nano10061189] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/18/2020] [Revised: 06/16/2020] [Accepted: 06/17/2020] [Indexed: 10/25/2022]
Abstract
In this paper, the compressive stress of pristine and coated vertically-aligned (VA) multi-walled (MW) carbon nanotube (CNT) pillars were investigated using flat-punch nano-indentation. VA-MWCNT pillars of various diameters (30-150 µm) grown by low-pressure chemical vapor deposition on silicon wafer. A conformal brittle coating of niobium-titanium-nitride with high superconductivity temperature was deposited on the VA-MWCNT pillars using atomic layer deposition. The coating together with the pillars could form a superconductive vertical interconnect. The indentation tests showed foam-like behavior of pristine CNTs and ceramic-like fracture of conformal coated CNTs. The compressive strength and the elastic modulus for pristine CNTs could be divided into three regimes of linear elastic, oscillatory plateau, and exponential densification. The elastic modulus of pristine CNTs increased for a smaller pillar diameter. The response of the coated VA-MWCNTs depended on the diffusion depth of the coating in the pillar and their elastic modulus increased with pillar diameter due to the higher sidewall area. Tuning the material properties by conformal coating on various diameter pillars enhanced the mechanical performance and the vertical interconnect access (via) reliability. The results could be useful for quantum computing applications that require high-density superconducting vertical interconnects and reliable operation at reduced temperatures.
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Roumeli E, Diamantopoulou M, Serra-Garcia M, Johanns P, Parcianello G, Daraio C. Characterization of Vertically Aligned Carbon Nanotube Forests Grown on Stainless Steel Surfaces. NANOMATERIALS 2019; 9:nano9030444. [PMID: 30875999 PMCID: PMC6474093 DOI: 10.3390/nano9030444] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Revised: 02/26/2019] [Accepted: 02/27/2019] [Indexed: 11/16/2022]
Abstract
Vertically aligned carbon nanotube (CNT) forests are a particularly interesting class of nanomaterials, because they combine multifunctional properties, such as high energy absorption, compressive strength, recoverability, and super-hydrophobicity with light weight. These characteristics make them suitable for application as coating, protective layers, and antifouling substrates for metallic pipelines and blades. Direct growth of CNT forests on metals offers the possibility of transferring the tunable CNT functionalities directly onto the desired substrates. Here, we focus on characterizing the structure and mechanical properties, as well as wettability and adhesion, of CNT forests grown on different types of stainless steel. We investigate the correlations between composition and morphology of the steel substrates with the micro-structure of the CNTs and reveal how the latter ultimately controls the mechanical and wetting properties of the CNT forest. Additionally, we study the influence of substrate morphology on the adhesion of CNTs to their substrate. We highlight that the same structure-property relationships govern the mechanical performance of CNT forests grown on steels and on Si.
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Affiliation(s)
- Eleftheria Roumeli
- Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology (ETH Zurich), 8092 Zurich, Switzerland.
- Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, USA.
| | - Marianna Diamantopoulou
- Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology (ETH Zurich), 8092 Zurich, Switzerland.
| | - Marc Serra-Garcia
- Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology (ETH Zurich), 8092 Zurich, Switzerland.
- Department of Physics, Swiss Federal Institute of Technology (ETH Zurich), 8092 Zurich, Switzerland.
| | - Paul Johanns
- Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology (ETH Zurich), 8092 Zurich, Switzerland.
| | | | - Chiara Daraio
- Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, USA.
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7
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Brown J, Davis BF, Maschmann MR. Precision Milling of Carbon Nanotube Forests Using Low Pressure Scanning Electron Microscopy. J Vis Exp 2017. [PMID: 28190032 DOI: 10.3791/55149] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
A nanoscale fabrication technique appropriate for milling carbon nanotube (CNT) forests is described. The technique utilizes an environmental scanning electron microscope (ESEM) operating with a low pressure water vapor ambient. In this technique, a portion of the electron beam interacts with the water vapor in the vicinity of the CNT sample, dissociating the water molecules into hydroxyl radicals and other species by radiolysis. The remainder of the electron beam interacts with the CNT forest sample, making it susceptible to oxidation from the chemical products of radiolysis. This technique may be used to trim a selected region of an individual CNT, or it may be used to remove hundreds of cubic microns of material by adjusting ESEM parameters. The machining resolution is similar to the imaging resolution of the ESEM itself. The technique produces only small quantities of carbon residue along the boundaries of the cutting zone, with minimal effect on the native structural morphology of the CNT forest.
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Affiliation(s)
- Josef Brown
- Department of Mechanical & Aerospace Engineering, University of Missouri
| | - Benjamin F Davis
- Department of Mechanical & Aerospace Engineering, University of Missouri
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Davis BF, Yan X, Muralidharan N, Oakes L, Pint CL, Maschmann MR. Electrically Conductive Hierarchical Carbon Nanotube Networks with Tunable Mechanical Response. ACS APPLIED MATERIALS & INTERFACES 2016; 8:28004-28011. [PMID: 27689747 DOI: 10.1021/acsami.6b10726] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Small diameter carbon nanotube (CNTs) are synthesized directly from a parent CNT forest using a floating catalyst chemical vapor deposition (CVD) method. To support a new CNT generation from an existing forest, an alumina coating was applied to the CNT forest using atomic layer deposition (ALD). The new generation of small diameter CNTs (8 nm average) surround the first generation, filling the interstitial regions. The hierarchical forests exhibit a 5-10-fold increase in stiffness, and the two generations are electrically addressable in spite of the interfacial alumina layer between them. This work enables the design of complex CNT architectures with hierarchical features that bring tailored properties such as high specific surface area and robust mechanical properties that can benefit a range of applications.
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Affiliation(s)
- Benjamin F Davis
- Department of Mechanical & Aerospace Engineering, University of Missouri , Columbia, Missouri 65211, United States
| | - Xingyi Yan
- Department of Mechanical & Aerospace Engineering, University of Missouri , Columbia, Missouri 65211, United States
| | - Nitin Muralidharan
- Department of Mechanical Engineering and Interdisciplinary Materials Science Program, Vanderbilt University , Nashville, Tennessee 37235, United States
| | - Landon Oakes
- Department of Mechanical Engineering and Interdisciplinary Materials Science Program, Vanderbilt University , Nashville, Tennessee 37235, United States
| | - Cary L Pint
- Department of Mechanical Engineering and Interdisciplinary Materials Science Program, Vanderbilt University , Nashville, Tennessee 37235, United States
| | - Matthew R Maschmann
- Department of Mechanical & Aerospace Engineering, University of Missouri , Columbia, Missouri 65211, United States
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Shin SR, Shin C, Memic A, Shadmehr S, Miscuglio M, Jung HY, Jung SM, Bae H, Khademhosseini A, Tang X(S, Dokmeci MR. Aligned carbon nanotube-based flexible gel substrates for engineering bio-hybrid tissue actuators. ADVANCED FUNCTIONAL MATERIALS 2015; 25:4486-4495. [PMID: 27134620 PMCID: PMC4849195 DOI: 10.1002/adfm.201501379] [Citation(s) in RCA: 93] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Muscle-based biohybrid actuators have generated significant interest as the future of biorobotics but so far they move without having much control over their actuation behavior. Integration of microelectrodes into the backbone of these systems may enable guidance during their motion and allow precise control over these actuators with specific activation patterns. Here, we addressed this challenge by developing aligned CNT forest microelectrode arrays and incorporated them into scaffolds for stimulating the cells. Aligned CNTs were successfully embedded into flexible and biocompatible hydrogel exhibiting excellent anisotropic electrical conductivity. Bioactuators were then engineered by culturing cardiomyocytes on the CNT microelectrode-integrated hydrogel constructs. The resulting cardiac tissue showed homogeneous cell organization with improved cell-to-cell coupling and maturation, which was directly related to the contractile force of muscle tissue. This centimeter-scale bioactuator has excellent mechanical integrity, embedded microelectrodes and is capable of spontaneous actuation behavior. Furthermore, we demonstrated that a biohybrid machine can be controlled by an external electrical field provided by the integrated CNT microelectrode arrays. In addition, due to the anisotropic electrical conductivity of the electrodes provided from aligned CNTs, significantly different excitation thresholds were observed in different configurations such as the ones in parallel vs. perpendicular direction to the CNT alignment.
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Affiliation(s)
- Su Ryon Shin
- Biomaterials Innovation Research Center, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02139, USA. Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA
| | - Courtney Shin
- Biomaterials Innovation Research Center, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02139, USA. Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Adnan Memic
- Center of Nanotechnology, King Abdulaziz University, Jeddah, 21589, Saudi Arabia
| | - Samaneh Shadmehr
- Department of Chemistry & Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Ave. West, Waterloo, Ontario, N2L 3G1, Canada
| | - Mario Miscuglio
- Biomaterials Innovation Research Center, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02139, USA. Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Hyun Young Jung
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, USA
| | - Sung Mi Jung
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Hojae Bae
- College of Animal Bioscience and Technology, Department of Bioindustrial Technologies, Konkuk University, Hwayang-dong, Kwangjin-gu, Seoul 143-701, Korea
| | - Ali Khademhosseini
- Biomaterials Innovation Research Center, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02139, USA. Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Department of Physics, King Abdulaziz University, Jeddah 21569, Saudi Arabia. Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA. Department of Maxillofacial Biomedical Engineering and Institute of Oral Biology, School of Dentistry, Kyung Hee University, Seoul 130-701, Republic of Korea
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Zeng Z, Gui X, Gan Q, Lin Z, Zhu Y, Zhang W, Xiang R, Cao A, Tang Z. Integrated random-aligned carbon nanotube layers: deformation mechanism under compression. NANOSCALE 2014; 6:1748-1755. [PMID: 24352698 DOI: 10.1039/c3nr04667b] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Carbon nanotubes have the potential to construct highly compressible and elastic macroscopic structures such as films, aerogels and sponges. The structure-related deformation mechanism determines the mechanical behavior of those structures and niche applications. Here, we show a novel strategy to integrate aligned and random nanotube layers and reveal their deformation mechanism under uniaxial compression with a large range of strain and cyclic testing. Integrated nanotube layers deform sequentially with different mechanisms due to the distinct morphology of each layer. While the aligned layer forms buckles under compression, nanotubes in the random layer tend to be parallel and form bundles, resulting in the integration of quite different properties (strength and stiffness) and correspondingly distinct plateau regions in the stress-strain curves. Our results indicate a great promise of constructing hierarchical carbon nanotube structures with tailored energy absorption properties, for applications such as cushioning and buffering layers in microelectromechanical systems.
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Affiliation(s)
- Zhiping Zeng
- State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, P. R. China.
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Abadi PPSS, Maschmann MR, Baur JW, Graham S, Cola BA. Deformation response of conformally coated carbon nanotube forest. NANOTECHNOLOGY 2013; 24:475707. [PMID: 24192522 DOI: 10.1088/0957-4484/24/47/475707] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The deformation mechanism and mechanical properties of carbon nanotube (CNT) forests conformally coated with alumina using atomic layer deposition (ALD) are investigated using in situ and ex situ micro-indentation. While micro-indentation of a CNT forest coated with a thin discontinuous layer using 20 ALD cycles results in a deformation response similar to the response of uncoated CNT forests, a similar test on a CNT forest coated with a sufficiently thick and continuous layer using 100 ALD cycles causes fracture of both the alumina coatings and the core CNTs. With a 10 nm coating, 4-fold and 14-fold stiffness increases are measured using a flat punch and a Berkovich tip, respectively. Indentation testing with the Berkovich tip also reveals increased recoverability at relatively low strains. The results show that ALD coated CNT forests could be useful for applications that require higher stiffness or recoverability. Also, fracturing of the nanotubes shows that upper limits exist in the loading of conformally coated CNT forests.
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Pathak S, Mohan N, Decolvenaere E, Needleman A, Bedewy M, Hart AJ, Greer JR. Local relative density modulates failure and strength in vertically aligned carbon nanotubes. ACS NANO 2013; 7:8593-8604. [PMID: 24001107 DOI: 10.1021/nn402710j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Micromechanical experiments, image analysis, and theoretical modeling revealed that local failure events and compressive stresses of vertically aligned carbon nanotubes (VACNTs) were uniquely linked to relative density gradients. Edge detection analysis of systematically obtained scanning electron micrographs was used to quantify a microstructural figure-of-merit related to relative local density along VACNT heights. Sequential bottom-to-top buckling and hardening in stress-strain response were observed in samples with smaller relative density at the bottom. When density gradient was insubstantial or reversed, bottom regions always buckled last, and a flat stress plateau was obtained. These findings were consistent with predictions of a 2D material model based on a viscoplastic solid with plastic non-normality and a hardening-softening-hardening plastic flow relation. The hardening slope in compression generated by the model was directly related to the stiffness gradient along the sample height, and hence to the local relative density. These results demonstrate that a microstructural figure-of-merit, the effective relative density, can be used to quantify and predict the mechanical response.
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Affiliation(s)
- Siddhartha Pathak
- Materials Science, California Institute of Technology (Caltech) , Pasadena, California, United States
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