WO2022154985A1 - Carbon nanotube constructs having a density gradient and methods for preparing same - Google Patents
Carbon nanotube constructs having a density gradient and methods for preparing same Download PDFInfo
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Classifications
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- C—CHEMISTRY; METALLURGY
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- D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
Definitions
- the present disclosure relates to carbon nanotubes and constructs formed therefrom.
- Carbon nanotubes are high aspect ratio materials having a variety of mechanical, electrical, and thermal properties that make them attractive for bottom-up construction of aerogels, yams and polymer composites, among other designed structures. Processing of carbon nanotubes has largely focused on spinning carbon nanotubes and bundles thereof into maximal density fibers/yams as a replacement for traditional carbon fibers, such as those used in the formation of polymer composites. However, the potential of carbon nanotubes and their constructs in polymer composites is not fully realized by this carbon fiber replacement approach. In particular, the maximal density structures may reduce the infiltration and integration of polymers. Other advantages to afford improved CNT-matrix interactions include the increased contribution of the interfacial polymer properties to the bulk properties.
- the presence of strongly attractive surfaces can appreciably improve the properties of the polymer molecules in the vicinity of the CNTs.
- the infiltration of polymer may lead to improved stress transfer as the mediating polymer layer is stronger than neat CNT-CNT interfaces.
- the present disclosure is directed to carbon nanotube constructs, including a plurality of first regions including a first plurality of carbon nanotube bundles that are aligned substantially in parallel; a plurality of second regions including a second plurality of carbon nanotube bundles that extend from the plurality of first regions and are non-aligned with the first plurality of carbon nanotube bundles in the plurality of first regions; and an interpenetration region between the plurality of first regions in which the second plurality of carbon nanotubes within second regions extending from one or more adjacent first regions interpenetrate one another.
- the present disclosure is directed to methods that include: providing a plurality of carbon nanotube bundles; and converting the plurality of carbon nanotube bundles into a carbon nanotube construct by applying at least one of stretching force, compression, or elastocapillary coalescence, wherein the carbon nanotube construct includes: a plurality of first regions including a first plurality of carbon nanotubes that are aligned substantially in parallel; a plurality of second regions including a second plurality of carbon nanotubes that extend from the plurality of first regions and are non-aligned with the first plurality of carbon nanotubes in the plurality of first regions; and an interpenetration region between the plurality of first regions in which the second plurality of carbon nanotubes within second regions extending from one or more adjacent first regions interpenetrate one another.
- FIG. 1 is a diagram of a carbon nanotube assembly having tertiary structure.
- FIG. 2 is a cross-sectional diagram of a portion of a carbon nanotube construct of the present disclosure.
- FIGS. 3A and 3B show diagrams of carbon nanotube constructs having additional density variation on the macroscale.
- FIGS. 4 and 5 are plots of specific strength versus specific modulus for carbon nanotube yams and sheets, respectively, produced through various post-processing techniques.
- the present disclosure relates to carbon nanotubes and constructs formed therefrom, including polymer composites that include carbon nanotube constructs having regions of variable carbon nanotube density.
- carbon nanotube constructs disclosed herein include three- dimensional architectures formed from carbon nanotubes as primary structural components.
- regions of variable carbon nanotube density including higher-order carbon nanotube structures having zones with variable density, can be introduced to form complex architectures, as explained further herein.
- Such carbon nanotube constructs may exhibit enhanced mechanical properties and can be processed further to create polymer composites.
- Carbon nanotube constructs are macroscale architectures prepared from micro- and nanoscale assemblies of carbon nanotubes.
- the macroscale architecture of carbon nanotube constructs may also include regions of variable density created through interpenetration of neighboring microscale carbon nanotube assemblies that define the construct.
- the regions of variable density may enhance the impregnation with polymeric materials (polymer matrices or polymer resins), wetting, and improved space filling, particularly when compared to densely organized carbon materials, such as well-packed carbon nanotube yams.
- carbon nanotube constructs can exhibit progressive failure modes in which the architecture can sustain increased amounts of carbon nanotube damage prior to catastrophic failure, in contrast to the sudden failure and elastic recoil (ballistic failure) observed in dense carbon fiber-based structures.
- Structural redundancy and enhanced stress transmission throughout the interpenetrating networks within a carbon nanotube construct can allow stored strain energy to dissipate gradually, reducing ballistic failure and further damage progression to neighboring zones of the carbon nanotube construct and/or the surrounding polymer matrix.
- Carbon nanotubes represent the primary structural component (building block) of the carbon nanotube constructs.
- “carbon nanotubes” are diverse carbon-based structures that may include single-wall carbon nanotubes, multi-wall carbon nanotubes, double-wall carbon nanotubes, few-wall carbon nanotubes, and mixtures thereof.
- carbon nanotubes can be separated and/or enriched based on particular properties such as chirality, electrical conductivity, thermal conductivity, diameter, length, number of walls, defect density, and any combination of these properties.
- Suitable carbon nanotubes can have a ratio of diameter to length (aspect ratio) of at least about 10 3 , which can be an aspect ratio in a range of about 10 3 to about 10 8 in some embodiments. While carbon nanotube lengths may vary according to synthesis methods, suitable carbon nanotubes may have a length of at least about 100 microns in some embodiments.
- Carbon nanotube constructs disclosed herein can also be formed in whole or in part from carbon nanotubes functionalized with various surface modifications and substitutions.
- Functionalization may be employed, for example, to attenuate or enhance intermolecular van der Waals forces and enhance affinity with solvents, polymers, and/or polymer resins.
- Functionalization can also include various crosslinking chemistries that facilitate covalent and non-covalent linking between carbon nanotubes and/or polymer matrix for improved material properties and stress transfer.
- a wide range of techniques for functionalizing carbon nanotubes and functional groups introduced thereto will be familiar to one having ordinary skill in the art.
- secondary structures may develop from linear networks of carbon nanotubes oriented in a parallel or near- parallel fashion.
- Such linear networks of carbon nanotubes may be referred to as “carbon nanotube bundles” and can have diameters that range from about 30 nm or more, such as within a range of 20 nm to 75 nm or 30 nm to 50 nm, depending on the method of synthesis.
- Carbon nanotube bundles may be obtained, for example, by floating catalyst chemical vapor deposition (FCCVD), followed by various post-processing methods.
- Carbon nanotubes generated by FCCVD may include carbon nanotubes of various lengths up to about 1 mm or more, which can be processed to form low-density aerogels and/or incorporated into polymer composites using processes analogous to those used for comparatively high-density carbon fibers.
- FCCVD synthesis methods can also be adapted for continuous collection and processing. While carbon nanotubes prepared by FCCVD may be particularly suitable in the disclosure herein, the principles of the present disclosure are also applicable to carbon nanotubes produced by other techniques such as arc discharge, laser oven, flame synthesis, chemical vapor deposition, and the like.
- Carbon nanotube bundles can interface to form larger tertiary structures (or “carbon nanotube assemblies”) that include interpenetrating networks of carbon nanotubes, including “bristly” carbon nanotube assemblies containing three-dimensional mixtures containing subpopulations of both substantially parallel- and substantially non-parallel-oriented carbon nanotube bundles.
- “Substantially non-parallel-oriented” carbon nanotube bundles include any carbon nanotube bundle orientation that is not oriented substantially parallel with respect to another carbon nanotube bundle, particularly a plurality of carbon nanotube bundles aligned substantially in parallel, and is inclusive of carbon nanotube bundles oriented perpendicular to another carbon nanotube bundle and carbon nanotube bundles that are oriented irregularly with respect to another carbon nanotube bundle (any non-perpendicular angle except for parallel alignment).
- At least a majority of the carbon nanotube bundles arranged in a non-aligned fashion with parallel- aligned carbon nanotube bundles are arranged in a non-perpendicular fashion with respect to the parallel-aligned carbon nanotube bundles, more preferably in an irregular fashion with respect to the parallel-aligned carbon nanotube bundles.
- a plurality of non-aligned carbon nanotubes bundles may be oriented at a plurality of non-perpendicular angles in the constructs disclosed herein.
- Carbon nanotube construct 300b in FIG. 3B has spatially distributed density in two dimensions with high-density zones 302 and low-density zones 304. While shown in a checkerboard pattern in FIG. 3B, it is to be appreciated that other regular spatial arrangements for high-density zones 302 and low-density zones 304 also reside within the scope of the present disclosure. Likewise, irregular arrangements of high-density zones 302 and low-density zones 304 in two-dimensional constructs also reside within the scope of the present disclosure. High- density zones 302 and low-density zones 304 can be produced by various post-processing methods described below.
- Post-processing methods can also combine techniques, including extensional stretching and/or compression in the presence of at least one of a solvent, polymer solution containing monomers, prepolymers, and/or polymers, or an acid.
- acid treatment can be combined with extensional stretching, which may improve debundling by solvation and removal of byproducts.
- Post-processing techniques may also include covalently crosslinking the carbon nanotubes within a carbon nanotube construct to enhance stress transfer throughout the carbon nanotube network.
- Illustrative crosslinking techniques may include for example, irradiation by e- beam, plasma, gamma radiation, and the like, and/or by the use of crosslinking chemistry.
- Element 3 wherein the plurality of second regions have a local density in a range of about 0.5 g/cm 3 to about 1.0 g/cm 3 .
- Element 12 wherein the carbon nanotube construct is a yam.
- Element 14 wherein the polymer matrix is present within at least the interpenetration region and/or the plurality of second regions.
- Embodiment B further including: generating a three-dimensional shape from the carbon nanotube construct by a laying up process.
- Element 19 wherein the plurality of second regions have a local density in a range of about 0.5 g/cm 3 to about 1.0 g/cm 3 .
- Element 20 wherein converting comprises applying tension to the carbon nanotube bundles.
- illustrative combinations applicable to A include, but are not limited to, A and Element 1, A and Element 2, A and Element 3, A and Element 4, A and Element 5, A and Element 6, A and Element 7, A and Element 8, A and Element 9, A and Element 10, A and Element 11, A and Element 12, A and Element 13, A and Element 14, A and Element 15, and A and Element 16.
- Illustrative combinations applicable to B include, but are not limited to, B and Element 17, B and Element 18, B and Element 19, B and Element 20, and B and Element 2E
- compositions described herein may be free of any component, or composition not expressly recited or disclosed herein. Any method may lack any step not recited or disclosed herein.
Abstract
Carbon nanotube constructs can include a plurality of first regions including a first plurality of carbon nanotube bundles that are aligned substantially in parallel; a plurality of second regions including a second plurality of carbon nanotube bundles that extend from the plurality of first regions and are non-aligned with the first plurality of carbon nanotube bundles in the plurality of first regions; and an interpenetration region between the plurality of first regions in which the second plurality of carbon nanotubes within second regions extending from one or more adjacent first regions interpenetrate one another. Methods can include providing a plurality of carbon nanotube bundles; and converting the plurality of carbon nanotube bundles into a carbon nanotube construct by applying at least one of stretching force, compression, or elastocapillary coalescence.
Description
CARBON NANOTUBE CONSTRUCTS HAVING A DENSITY GRADIENT AND METHODS FOR PREPARING SAME
FIELD OF THE INVENTION
[0001] The present disclosure relates to carbon nanotubes and constructs formed therefrom.
BACKGROUND OF THE INVENTION
[0002] Carbon nanotubes (CNTs) are high aspect ratio materials having a variety of mechanical, electrical, and thermal properties that make them attractive for bottom-up construction of aerogels, yams and polymer composites, among other designed structures. Processing of carbon nanotubes has largely focused on spinning carbon nanotubes and bundles thereof into maximal density fibers/yams as a replacement for traditional carbon fibers, such as those used in the formation of polymer composites. However, the potential of carbon nanotubes and their constructs in polymer composites is not fully realized by this carbon fiber replacement approach. In particular, the maximal density structures may reduce the infiltration and integration of polymers. Other advantages to afford improved CNT-matrix interactions include the increased contribution of the interfacial polymer properties to the bulk properties. The presence of strongly attractive surfaces can appreciably improve the properties of the polymer molecules in the vicinity of the CNTs. The greater the fraction of polymer modified by the presence of CNTs, the better the bulk properties may become. Further, the infiltration of polymer may lead to improved stress transfer as the mediating polymer layer is stronger than neat CNT-CNT interfaces.
[0003] In addition to the foregoing, dense yams, due to the stochastic nature of the spinning process, may show a significant population of inaccessible voids that may act as defects, thereby reducing damage tolerance. Thus, the need remains for carbon nanotube architectures having enhanced reinforcement efficiency, fewer inaccessible voids and improved polymer infiltration compatibility for composite applications.
SUMMARY OF THE INVENTION
[0004] In some aspects, the present disclosure is directed to carbon nanotube constructs, including a plurality of first regions including a first plurality of carbon nanotube bundles that are aligned substantially in parallel; a plurality of second regions including a second plurality of carbon nanotube bundles that extend from the plurality of first regions and are non-aligned with the first plurality of carbon nanotube bundles in the plurality of first regions; and an interpenetration region between the plurality of first regions in which the second plurality of carbon nanotubes within second regions extending from one or more adjacent first regions interpenetrate one another.
[0005] In some or other aspects, the present disclosure is directed to methods that include: providing a plurality of carbon nanotube bundles; and converting the plurality of carbon nanotube bundles into a carbon nanotube construct by applying at least one of stretching force, compression, or elastocapillary coalescence, wherein the carbon nanotube construct includes: a plurality of first regions including a first plurality of carbon nanotubes that are aligned substantially in parallel; a plurality of second regions including a second plurality of carbon nanotubes that extend from the plurality of first regions and are non-aligned with the first plurality of carbon nanotubes in the plurality of first regions; and an interpenetration region between the plurality of first regions in which the second plurality of carbon nanotubes within second regions extending from one or more adjacent first regions interpenetrate one another.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The following figures are included to illustrate certain aspects of the disclosure, and should not be viewed as exclusive configurations. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.
[0007] FIG. 1 is a diagram of a carbon nanotube assembly having tertiary structure.
[0008] FIG. 2 is a cross-sectional diagram of a portion of a carbon nanotube construct of the present disclosure.
[0009] FIGS. 3A and 3B show diagrams of carbon nanotube constructs having additional density variation on the macroscale.
[0010] FIGS. 4 and 5 are plots of specific strength versus specific modulus for carbon nanotube yams and sheets, respectively, produced through various post-processing techniques.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The present disclosure relates to carbon nanotubes and constructs formed therefrom, including polymer composites that include carbon nanotube constructs having regions of variable carbon nanotube density. Particularly, carbon nanotube constructs disclosed herein include three- dimensional architectures formed from carbon nanotubes as primary structural components. Through the application of post-processing techniques, regions of variable carbon nanotube density, including higher-order carbon nanotube structures having zones with variable density, can be introduced to form complex architectures, as explained further herein. Such carbon nanotube constructs may exhibit enhanced mechanical properties and can be processed further to create polymer composites.
[0012] Carbon nanotube constructs are macroscale architectures prepared from micro- and nanoscale assemblies of carbon nanotubes. The macroscale architecture of carbon nanotube
constructs may also include regions of variable density created through interpenetration of neighboring microscale carbon nanotube assemblies that define the construct. The regions of variable density may enhance the impregnation with polymeric materials (polymer matrices or polymer resins), wetting, and improved space filling, particularly when compared to densely organized carbon materials, such as well-packed carbon nanotube yams.
[0013] As a structural material, carbon nanotube constructs can exhibit progressive failure modes in which the architecture can sustain increased amounts of carbon nanotube damage prior to catastrophic failure, in contrast to the sudden failure and elastic recoil (ballistic failure) observed in dense carbon fiber-based structures. Structural redundancy and enhanced stress transmission throughout the interpenetrating networks within a carbon nanotube construct can allow stored strain energy to dissipate gradually, reducing ballistic failure and further damage progression to neighboring zones of the carbon nanotube construct and/or the surrounding polymer matrix.
[0014] The architecture of the carbon nanotube constructs disclosed herein can be described in terms of a structural hierarchy. Carbon nanotubes represent the primary structural component (building block) of the carbon nanotube constructs. As used herein, “carbon nanotubes” are diverse carbon-based structures that may include single-wall carbon nanotubes, multi-wall carbon nanotubes, double-wall carbon nanotubes, few-wall carbon nanotubes, and mixtures thereof. In some embodiments, carbon nanotubes can be separated and/or enriched based on particular properties such as chirality, electrical conductivity, thermal conductivity, diameter, length, number of walls, defect density, and any combination of these properties. Suitable carbon nanotubes can have a ratio of diameter to length (aspect ratio) of at least about 103, which can be an aspect ratio in a range of about 103 to about 108 in some embodiments. While carbon nanotube lengths may vary according to synthesis methods, suitable carbon nanotubes may have a length of at least about 100 microns in some embodiments.
[0015] Carbon nanotube constructs disclosed herein can also be formed in whole or in part from carbon nanotubes functionalized with various surface modifications and substitutions. Functionalization may be employed, for example, to attenuate or enhance intermolecular van der Waals forces and enhance affinity with solvents, polymers, and/or polymer resins. Functionalization can also include various crosslinking chemistries that facilitate covalent and non-covalent linking between carbon nanotubes and/or polymer matrix for improved material properties and stress transfer. A wide range of techniques for functionalizing carbon nanotubes and functional groups introduced thereto will be familiar to one having ordinary skill in the art.
[0016] As the intermolecular distance between the carbon nanotubes decreases, secondary structures may develop from linear networks of carbon nanotubes oriented in a parallel or near-
parallel fashion. Such linear networks of carbon nanotubes may be referred to as “carbon nanotube bundles” and can have diameters that range from about 30 nm or more, such as within a range of 20 nm to 75 nm or 30 nm to 50 nm, depending on the method of synthesis. Carbon nanotube bundles may be obtained, for example, by floating catalyst chemical vapor deposition (FCCVD), followed by various post-processing methods. Carbon nanotubes generated by FCCVD may include carbon nanotubes of various lengths up to about 1 mm or more, which can be processed to form low-density aerogels and/or incorporated into polymer composites using processes analogous to those used for comparatively high-density carbon fibers. FCCVD synthesis methods can also be adapted for continuous collection and processing. While carbon nanotubes prepared by FCCVD may be particularly suitable in the disclosure herein, the principles of the present disclosure are also applicable to carbon nanotubes produced by other techniques such as arc discharge, laser oven, flame synthesis, chemical vapor deposition, and the like.
[0017] Carbon nanotube bundles can interface to form larger tertiary structures (or “carbon nanotube assemblies”) that include interpenetrating networks of carbon nanotubes, including “bristly” carbon nanotube assemblies containing three-dimensional mixtures containing subpopulations of both substantially parallel- and substantially non-parallel-oriented carbon nanotube bundles. “Substantially non-parallel-oriented” carbon nanotube bundles include any carbon nanotube bundle orientation that is not oriented substantially parallel with respect to another carbon nanotube bundle, particularly a plurality of carbon nanotube bundles aligned substantially in parallel, and is inclusive of carbon nanotube bundles oriented perpendicular to another carbon nanotube bundle and carbon nanotube bundles that are oriented irregularly with respect to another carbon nanotube bundle (any non-perpendicular angle except for parallel alignment). Preferably, at least a majority of the carbon nanotube bundles arranged in a non-aligned fashion with parallel- aligned carbon nanotube bundles are arranged in a non-perpendicular fashion with respect to the parallel-aligned carbon nanotube bundles, more preferably in an irregular fashion with respect to the parallel-aligned carbon nanotube bundles. A plurality of non-aligned carbon nanotubes bundles may be oriented at a plurality of non-perpendicular angles in the constructs disclosed herein.
[0018] Carbon nanotube assemblies can include a regional density gradient of carbon nanotube bundles in one or more dimensions between high-density regions, such as a high-density core, and adjacent low-density regions extending from and at least partially intertwined with the high-density regions. In some embodiments, density gradients of carbon nanotube assemblies between high- and low-density regions can be induced as a function of synthesis or through mechanical modification to lift ends of carbon nanotube bundles from a high-density region.
[0019] FIG. 1 is a diagram of a carbon nanotube assembly having tertiary structure. As shown, a carbon nanotube assembly 100 includes a relatively dense core that includes a first region 102 containing a plurality of carbon nanotube bundles 110 that are aligned substantially in parallel. The first region 102 has a first density (DI) associated with carbon nanotube bundles 110, each of which is formed from substantially linear networks of carbon nanotubes, and has a size defined by a radius 104. The carbon nanotube bundles 110 in first region 102 can afford a local density in a range of about 0.8 g/cm3 to about 2.0 g/cm3.
[0020] The carbon nanotube assembly 100 includes a second region 106 that includes a second plurality of carbon nanotube bundles 112 that extend from the first region 102 and that are non- aligned with the first plurality of carbon nanotube bundles 110 in the first region 102. In some embodiments, the second region 106 is formed from carbon nanotube bundles 112 that are arranged concentrically around the carbon nanotube bundles 110 in the first region 102, wherein the arrangement around the first region 102 is in a non-perpendicular fashion. The second region 106 has a density (D2) that is different than DI. Particularly, the density of D2 is less than DI (/.£., the first region 102 has a higher density of carbon nanotubes than does the second region 106). The second region 106 can also be described by a thickness 108 that is defined with respect to first region 102. Carbon nanotube assemblies disclosed herein can include a local density in the plurality of second regions 106 in a range of about 0.1 g/cm3 to about 1.0 g/cm3. In some embodiments of the carbon nanotube constructs, the percent by weight (wt%) of carbon nanotubes in the first regions 102 may be within a range of about 10 wt% to about 90 wt%, about 20 wt% to about 80 wt%, about 50 wt% to about 80 wt%, or about 30 wt% to about 70 wt%.
[0021] Carbon nanotube constructs having quaternary and higher order structures may be formed from multiple carbon nanotube assemblies 100, including interpenetrated carbon nanotube assemblies which can further combine to form larger architectures. FIG. 2 is a cross-sectional diagram of a carbon nanotube construct 200 of the present disclosure created by the interface of neighboring carbon nanotube assemblies 100a and 100b. As the inter-bundle distance 208 between the neighboring carbon nanotube assemblies 100a and 100b decreases, such as by mechanical or chemical post-processing methods discussed below, an interpenetration region 210 is formed as the second regions 106a and 106b extending from adjacent first regions 102a and 102b, respectively, interpenetrate one another. The interpenetration region 210 forms a mechanical interlock between neighboring carbon nanotube assemblies 100a and 100b that can enhance stress transfer between the structures. Interpenetration region 210 can also define an intermediate density (D3), where D1>D3>D2. In some embodiments, carbon nanotube constructs
can include one or more interpenetration regions 210 having a local density (D3) in the range of about 0.2 g/cm3 to about 1.5 g/cm3.
[0022] The degree of interaction and/ or depth of interpenetration in the interpenetration region 210 can be tuned, for example, by increasing the length of the second regions 106a and 106b, modifying the spatial ratio of distances 104a and 108a (similarly, 104b and 108b), increasing the volume fraction of carbon nanotube assemblies within 108a and 108b, and/or by modifying the overall aspect ratio of the carbon nanotube bundles/ assemblies that constitute the carbon nanotube construct 200.
[0023] Carbon nanotube constructs can also include higher order structures, such as fifth order, sixth order, etc., that are formed by the aggregation of quaternary structures to produce larger architectures having varying or gradient density between two or more density zones in which the localized density of carbon nanotube assemblies varies in a random, periodic, or geometric fashion, including checkerboard, weaves, and other analogous and/or mechanically beneficial structures. In other words, a first portion of the plurality of first regions and a second portion of the plurality of first regions may be arranged such that the local densities at various locations differ from one another. Fifth order carbon nanotube constructs can also include low density zones in predetermined locations to introduce ductile regions, living hinges, or stable failure points. FIGS. 3A and 3B show diagrams of carbon nanotube constructs that include fifth order structure and introduce zonal density variation on the macroscale among quaternary substructures. Carbon nanotube construct 300a in FIG. 3A has linearly distributed density gradients between high-density zones 302 having a greater relative average density of carbon nanotubes as compared to low-density zones 304. Such carbon nanotube constructs having linearly distributed density gradients can include larger architectures, such as banded carbon nanotube fibers or yams, sheets, fabrics, or aerogels.
[0024] Carbon nanotube construct 300b in FIG. 3B has spatially distributed density in two dimensions with high-density zones 302 and low-density zones 304. While shown in a checkerboard pattern in FIG. 3B, it is to be appreciated that other regular spatial arrangements for high-density zones 302 and low-density zones 304 also reside within the scope of the present disclosure. Likewise, irregular arrangements of high-density zones 302 and low-density zones 304 in two-dimensional constructs also reside within the scope of the present disclosure. High- density zones 302 and low-density zones 304 can be produced by various post-processing methods described below. Three-dimensional arrangements of high-density zones 304 and low-density zones 304 are also contemplated within the scope of the present disclosure as well.
[0025] Carbon nanotube constructs disclosed herein can have an average density in a range of about 0.25 g/cm3 to about 1.3 g/cm3. Carbon nanotube constructs can include one or more relatively high carbon nanotube density zones and one or more relatively low carbon nanotube density. In some embodiments, carbon nanotube constructs can include one or more high carbon nanotube density zones having a local density in a range of about 0.8 g/cm3 to about 2 g/cm3, and one or more relatively low carbon nanotube density having a local density in a range of about 0. 1 g/cm3 to about 1 g/cm3.
[0026] Carbon nanotube constructs disclosed herein can include an average relative volumetric fraction (V c/V o) in a range of about 0.1 to about 1 , wherein V c represents the volume of the carbon nanotubes and Vo represents the overall volume of the carbon nanotube construct, which may be similar to that of a polymer composite or aerogel in which the carbon nanotube constructs are present. In some embodiments, the relative volumetric fraction of carbon nanotubes in the high-density zones (VC/VO)H can be in a range of greater than about 0.8 to about 1. In some embodiments, the relative volumetric fraction of the carbon nanotubes in the low-density zones (VC/VO)L can be in a range of about 0.1 to about 0.8. For example, a carbon nanotube construct can have an average relative volumetric fraction (Vc/Vo) of about 0.5, where high-density zones have a relative volumetric fraction (Vc/V O)H of about 1.0 and the low-density zones have a relative volumetric fraction (VC/VO)L of about 0.3. Carbon nanotube constructs can include interpenetration regions having a relative volumetric fraction (Vc/Vo) that is in a range of about 5% to about 50% of that of the first regions, according to some embodiments.
[0027] Carbon nanotube constructs disclosed herein can be produced from low-density carbon nanotube structures such as sheets and loose yams that are consolidated by a number of postprocessing methods to enhance the strength of the material by aligning at least a fraction of carbon nanotubes along their longitudinal axes. Post-processing methods can also create defined density gradients within the material. Density gradients can be introduced at both the regional level within carbon nanotube assemblies (microscale) and at the zonal level within the carbon nanotube construct (macroscale), thereby producing carbon nanotube constructs having overall densities that fall at an intermediate level between unprocessed carbon nanotube bundles (such as as- collected FCCVD yam) and high density carbon fibers. Increasing the density of carbon nanotube constmct precursors can result from a reduction of void space and flattening of carbon nanotube bundle cross-sections, which increases contact between carbon nanotubes and may enhance stress transfer. Post-processing methods may also include the formation of polymer composites by impregnating the carbon nanotube constructs with polymeric compositions (e.g, polymers or polymer resins) and/or assembling the polymer composites into plied or wound stmctures.
[0028] In the course of producing carbon nanotube constructs of the present disclosure, carbon nanotubes may begin as low-density structures that are consolidated by a number of postprocessing techniques to increase mechanical strength, including dry or wet extensional drawing and/or transverse compression, wet processing, liquid-induced condensation (elastocapillary coalescence), and the like. Post-processing methods can also include mechanical and performance modification of carbon nanotube constructs by purification, crosslinking, and functionalization performed in combination with any other post-processing method. Densification of carbon nanotube constructs may be realized by any of the foregoing techniques or any combination thereof.
[0029] Extensional drawing methods include drawing carbon nanotubes that are fixed between tensile grips or on a roll-to-roll basis through a series of wheels with progressively increasing velocities. During drawing, carbon nanotube bundles align in a primary direction and undergo densification in an orthogonal direction. Varying degrees of alignment can also be obtained during extensional drawing where a carbon nanotube construct precursor modified to have zones with different densities prior to extension. Compression techniques can include densification of carbon nanotube bundles by uni- or biaxial compression orthogonal to the alignment direction, such as in a hot press/between rollers. Other two-dimensional gradient density patterns can be formed by non-uniform pressure application.
[0030] FIGS. 4 and 5 are plots of specific strength versus specific modulus for carbon nanotube yams and sheets, respectively, produced through various post-processing techniques. [0031] Post-processing methods may also incorporate densification of carbon nanotubes by “wet” methods in which precursors to carbon nanotube constructs are dipped in or sprayed with an evaporating non-polar solvent, such as acetone. In some embodiments, two-dimensional and three-dimensional gradient density patterns can be introduced into carbon nanotube construct precursors by elastocapillarity through the non-uniform application of solvent. Wet postprocessing methods can include batch processing, such as spray coating, or continuous processing, in which a carbon nanotube construct precursor is passed through a bath that includes one or more of a non-polar solvent, acid, or electrolyte. Wet post-processing methods also may include acid treatment of carbon nanotube construct precursors in order to remove impurities and enhance density by elastocapillary coalescence or by coagulation in anti-solvents. Suitable acids can include mineral acids such as sulfuric acid, and organic acids such as chlorosulfonic acid, and the like.
[0032] Post-processing methods can also combine techniques, including extensional stretching and/or compression in the presence of at least one of a solvent, polymer solution
containing monomers, prepolymers, and/or polymers, or an acid. For example, acid treatment can be combined with extensional stretching, which may improve debundling by solvation and removal of byproducts.
[0033] Post-processing techniques may also include covalently crosslinking the carbon nanotubes within a carbon nanotube construct to enhance stress transfer throughout the carbon nanotube network. Illustrative crosslinking techniques may include for example, irradiation by e- beam, plasma, gamma radiation, and the like, and/or by the use of crosslinking chemistry.
[0034] The carbon nanotube constructs described herein may be further processed into polymer composites through the infiltration of polymer or polymer resin into the carbon nanotube constructs, particularly within low-density and intermediate-density regions and zones, more particularly within the interpenetration zone between multiple constructs. By creating relatively low-density regions between carbon nanotube bundles within carbon nanotube constructs, channels are formed that increase infiltration of polymers and polymer resins into the constructs. Increased infiltration of polymers and polymer resins results a polymer composite in which the polymer matrix distribution is increased to improve matrix interactions with a greater proportion of the carbon nanotubes, rather than just the carbon nanotubes upon the surface of a carbon nanotube bundle. Increased polymer matrix distribution can result in an increase in stiffness, improved stress transmission, improved creep resistance, and damage tolerance in accordance to traditional concepts of continuum composite theory.
[0035] Methods disclosed herein also include infiltrating the carbon nanotube constructs with polymers or polymer-forming compositions to generate polymer composites. Polymer composite preparation methods can include the introduction of neat monomers or resins, or dissolved in a low viscosity solvent that can be removed by drying following infiltration. Following polymer infiltration, polymer composites can be further refined by tensile or compressive processing methods to remove excess polymer matrix without reducing the morphological advantages of the carbon nanotube constructs providing internal reinforcement.
[0036] Methods of carbon nanotube construct production can be adapted to the large volume production of carbon nanotube constructs and polymer composites that include fibers, yams, sheets, tapes, fabrics, aerogels, and the like. In order to fabricate three-dimensional shapes and parts, the post-processed carbon nanotube constructs can be generated by a laying up process in which carbon nanotube construct plies or sheets are laid up or layered into defined shapes and further consolidated to remove voids. Lay-up methods include manual techniques and continuous processes such as filament or tape winding onto drums or other forms. In these processes, tension can also be maintained during lay-up to modify alignment quality.
[0037] Example Embodiments
[0038] Embodiments disclosed herein include:
[0039] A. Carbon nanotube constructs, including a plurality of first regions including a first plurality of carbon nanotube bundles that are aligned substantially in parallel; a plurality of second regions including a second plurality of carbon nanotube bundles that extend from the plurality of first regions and are non-aligned with the first plurality of carbon nanotube bundles in the plurality of first regions; and an interpenetration region between the plurality of first regions in which the second plurality of carbon nanotubes within second regions extending from one or more adjacent first regions interpenetrate one another.
[0040] B. Methods that include: providing a plurality of carbon nanotube bundles; and converting the plurality of carbon nanotube bundles into a carbon nanotube construct by applying at least one of a stretching force or compression, wherein the carbon nanotube construct includes: a plurality of first regions including a first plurality of carbon nanotubes that are aligned substantially in parallel; a plurality of second regions including a second plurality of carbon nanotubes that extend from the plurality of first regions and are non-aligned with the first plurality of carbon nanotubes in the plurality of first regions; and an interpenetration region between the plurality of first regions in which the second plurality of carbon nanotubes within second regions extending from one or more adjacent first regions interpenetrate one another.
[0041] Embodiments A and B may have one or more of the following additional elements in any combination:
[0042] Element 1: wherein the plurality of first regions have a higher density of carbon nanotubes than the plurality of second regions.
[0043] Element 2: wherein the plurality of first regions have a local density in a range of about 0.8 g/cm3 to about 2.0 g/cm3.
[0044] Element 3: wherein the plurality of second regions have a local density in a range of about 0.5 g/cm3 to about 1.0 g/cm3.
[0045] Element 4: wherein the interpenetration region has a relative volumetric fraction that is at least about 50% of that of the plurality of first regions.
[0046] Element 5: wherein the interpenetration region has a volumetric fraction that is in a range of about 5% to about 50% of that of the plurality of first regions.
[0047] Element 6: wherein at least one of the first plurality of carbon nanotubes or the second plurality of carbon nanotubes comprises carbon nanotubes having an aspect ratio of at least about 103.
[0048] Element 7 : wherein at least one of the first plurality of carbon nanotubes or the second plurality of carbon nanotubes comprises carbon nanotubes having an aspect ratio in a range of about 103to about 108.
[0049] Element 8: wherein the first plurality of carbon nanotubes within the plurality of first regions have a cross-sectional radius of about 30 nm or greater.
[0050] Element 9: wherein the first plurality of carbon nanotubes comprises about 10 wt% to 90 wt% of the construct based upon a total weight of carbon nanotubes.
[0051] Element 10: a higher order structure comprising a first portion of the plurality of first regions and a second portion of the plurality of first regions that are arranged to have zonal densities differing from one another.
[0052] Element 11 : wherein the carbon nanotube construct is a sheet.
[0053] Element 12: wherein the carbon nanotube construct is a yam.
[0054] Element 13: A polymer composite, including: a polymer matrix; and the carbon nanotube construct of Embodiment A.
[0055] Element 14: wherein the polymer matrix is present within at least the interpenetration region and/or the plurality of second regions.
[0056] Element 15: wherein the carbon nanotube construct include an average relative volumetric fraction (Vc/Vo) in a range of about 0.1 to about 1, wherein Vc represents a carbon nanotube volume of the carbon nanotube construct and Vo represents an overall volume of the carbon nanotube construct.
[0057] Element 16: wherein converting the plurality of carbon nanotube bundles occurs in the presence of at least one of a solvent, polymer solution, or an acid.
[0058] Element 17: Embodiment B further including: generating a three-dimensional shape from the carbon nanotube construct by a laying up process.
[0059] Element 18: wherein the plurality of first regions have a local density in a range of about 0.8 g/cm3 to about 2.0 g/cm3.
[0060] Element 19: wherein the plurality of second regions have a local density in a range of about 0.5 g/cm3 to about 1.0 g/cm3.
[0061] Element 20: wherein converting comprises applying tension to the carbon nanotube bundles.
[0062] Element 21: The method of Embodiment B, further including: impregnating the carbon nanotube construct with a polymer matrix.
[0063] By way of non-limiting example, illustrative combinations applicable to A include, but are not limited to, A and Element 1, A and Element 2, A and Element 3, A and Element 4, A and
Element 5, A and Element 6, A and Element 7, A and Element 8, A and Element 9, A and Element 10, A and Element 11, A and Element 12, A and Element 13, A and Element 14, A and Element 15, and A and Element 16. Illustrative combinations applicable to B include, but are not limited to, B and Element 17, B and Element 18, B and Element 19, B and Element 20, and B and Element 2E
[0064] All documents described herein are incorporated by reference herein for purposes of all jurisdictions where such practice is allowed, including any priority documents and/or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific embodiments, while forms of the disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited thereby. For example, the compositions described herein may be free of any component, or composition not expressly recited or disclosed herein. Any method may lack any step not recited or disclosed herein. Likewise, the term “comprising” is considered synonymous with the term “including.” Whenever a method, composition, element or group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “is” preceding the recitation of the composition, element, or elements and vice versa.
[0065] One or more illustrative incarnations incorporating one or more invention elements are presented herein. Not all features of a physical implementation are described or shown in this application for the sake of clarity. It is understood that in the development of a physical embodiment incorporating one or more elements of the present invention, numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, business-related, government-related and other constraints, which vary by implementation and from time to time. While a developer's efforts might be timeconsuming, such efforts would be, nevertheless, a routine undertaking for those of ordinary skill in the art and having benefit of this disclosure.
[0066] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the embodiments of the present invention. At the
very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
[0067] Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed, including the lower limit and upper limit. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a- b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces.
[0068] Therefore, the present disclosure is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to one having ordinary skill in the art and having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present disclosure. The embodiments illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein.
Claims
1. A carbon nanotube construct, comprising: a plurality of first regions comprising a first plurality of carbon nanotube bundles that are aligned substantially in parallel; a plurality of second regions comprising a second plurality of carbon nanotube bundles that extend from the plurality of first regions and are non-aligned with the first plurality of carbon nanotube bundles in the plurality of first regions; and an interpenetration region between the plurality of first regions in which the second plurality of carbon nanotubes within second regions extending from one or more adjacent first regions interpenetrate one another.
2. The carbon nanotube construct of claim 1, wherein the plurality of first regions have a higher density of carbon nanotubes than the plurality of second regions.
3. The carbon nanotube construct of claim 1, wherein the plurality of first regions have a local density in a range of about 0.8 g/cm3 to about 2.0 g/cm3.
4. The carbon nanotube construct of claim 1, wherein the plurality of second regions have a local density in a range of about 0.5 g/cm3 to about 1.0 g/cm3.
5. The carbon nanotube construct of claim 1, wherein the interpenetration region has a relative volumetric fraction that is at least about 50% of that of the plurality of first regions.
6. The carbon nanotube construct of claim 1, wherein the interpenetration region has a volumetric fraction that is in a range of about 5% to about 50% of that of the plurality of first regions.
7. The carbon nanotube construct of claim 1, wherein at least one of the first plurality of carbon nanotubes or the second plurality of carbon nanotubes comprises carbon nanotubes having an aspect ratio of at least about 103.
8. The carbon nanotube construct of claim 1, wherein at least one of the first plurality of carbon nanotubes or the second plurality of carbon nanotubes comprises carbon nanotubes having an aspect ratio in a range of about 103to about 108.
The carbon nanotube construct of claim 1, wherein the first plurality of carbon nanotubes within the plurality of first regions have a cross-sectional radius of about 30 nm or greater. The carbon nanotube construct of claim 1, wherein the first plurality of carbon nanotubes comprises about 10 wt% to 90 wt% of the construct based upon a total weight of carbon nanotubes. The carbon nanotube construct of claim 1, further comprising: a higher order structure comprising a first portion of the plurality of first regions and a second portion of the plurality of first regions that are arranged to have zonal densities differing from one another. The carbon nanotube construct of claim 1, wherein the carbon nanotube construct is a sheet. The carbon nanotube construct of claim 1, wherein the carbon nanotube construct is a yam. A polymer composite, comprising: a polymer matrix; and the carbon nanotube construct of claim 1. The polymer composite of claim 14, wherein the polymer matrix is present within at least the interpenetration region and/or the plurality of second regions. The polymer composite of claim 15, wherein the carbon nanotube construct comprises an average relative volumetric fraction (Vc/V o) in a range of about 0.1 to about 1, wherein Vc represents a carbon nanotube volume of the carbon nanotube construct and Vo represents an overall volume of the carbon nanotube construct. A method comprising: providing a plurality of carbon nanotube bundles; and converting the plurality of carbon nanotube bundles into a carbon nanotube construct by applying at least one of a stretching force, compression, or elastocapillary coalescence, wherein the carbon nanotube construct comprises:
a plurality of first regions comprising a first plurality of carbon nanotubes that are aligned substantially in parallel; a plurality of second regions comprising a second plurality of carbon nanotubes that extend from the plurality of first regions and are non- aligned with the first plurality of carbon nanotubes in the plurality of first regions; and an interpenetration region between the plurality of first regions in which the second plurality of carbon nanotubes within second regions extending from one or more adjacent first regions interpenetrate one another. The method of claim 17, wherein converting the plurality of carbon nanotube bundles occurs in the presence of at least one of a solvent, a polymer solution, or an acid. The method of claim 17, further comprising: generating a three-dimensional shape from the carbon nanotube construct by a laying up process. The method of claim 17, wherein the plurality of first regions have a local density in a range of about 0.8 g/cm3 to about 2.0 g/cm3. The method of claim 17, wherein the plurality of second regions have a local density in a range of about 0.5 g/cm3 to about 1.0 g/cm3. The method of claim 17, wherein converting comprises applying tension to the carbon nanotube bundles. The method of claim 17, further comprising: impregnating the carbon nanotube construct with a polymer matrix.
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