U.S. patent application number 11/846672 was filed with the patent office on 2010-06-03 for method for functionalizing nanotubes and improved polymer-nanotube composites formed using same.
Invention is credited to Amy A. Hofstra, Jennifer L. Sample.
Application Number | 20100137528 11/846672 |
Document ID | / |
Family ID | 42223404 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100137528 |
Kind Code |
A1 |
Sample; Jennifer L. ; et
al. |
June 3, 2010 |
Method for Functionalizing Nanotubes and Improved Polymer-Nanotube
Composites Formed Using Same
Abstract
A polymerizable ligand comprising, in one embodiment, a
polyaromatic compound, with a terminal functional group,
non-covalently bonded to the sidewalls of carbon nanotubes. This
structure preserves the structural, mechanical, electrical, and
electromechanical properties of the CNTs and ensures that an
unhindered functional group is available to bond with an extended
polymer matrix thereby resulting in an improved polymer-nanotube
composite.
Inventors: |
Sample; Jennifer L.;
(Bethesda, MD) ; Hofstra; Amy A.; (Greenbelt,
MD) |
Correspondence
Address: |
THE JOHNS HOPKINS UNIVERSITYAPPLIED PHYSICS LABORA;OFFICE OF PATENT
COUNSEL
11100 JOHNS HOPKINS ROAD, MAIL STOP 7-156
LAUREL
MD
20723-6099
US
|
Family ID: |
42223404 |
Appl. No.: |
11/846672 |
Filed: |
August 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60823769 |
Aug 29, 2006 |
|
|
|
Current U.S.
Class: |
525/455 ;
585/435; 585/469; 977/847 |
Current CPC
Class: |
B82Y 40/00 20130101;
B82Y 30/00 20130101; C01B 32/174 20170801; C07C 15/60 20130101;
C07C 15/56 20130101; C07C 2603/24 20170501 |
Class at
Publication: |
525/455 ;
585/435; 585/469; 977/847 |
International
Class: |
C08F 283/00 20060101
C08F283/00; C07C 15/28 20060101 C07C015/28; C07C 15/02 20060101
C07C015/02 |
Goverment Interests
STATEMENT OF GOVERNMENTAL INTEREST
[0002] This invention was made with Government support under
National Aeronautics and Space Administration grant no. NNG05GR51A.
The Government has certain rights in the invention.
Claims
1. A method for providing a polymerizable functionality to carbon
nanotubes (CNTs), the method comprising the step of non-covalently
bonding a polymerizable ligand to the CNTs.
2. The method of claim 1, wherein the polymerizable ligand
comprises a polyaromatic molecule with a polymerizable group
attached thereto.
3. The method of claim 2, wherein the polyaromatic molecule
comprises a polyaromatic hydrocarbon.
4. The method of claim 3, wherein the polyaromatic hydrocarbon
comprises anthracene.
5. The method of claim 2, wherein the polymerizable group comprises
a styryl group.
6. The method of claim 2, wherein the polymerizable group comprises
a vinyl group.
7. The method of claim 1, wherein the polymerizable ligand
comprises vinylanthracene.
8. The method of claim 1, wherein the polymerizable ligand is
bonded to the sidewalls of the CNTs.
9. The method of claim 1, further comprising the step of covalently
bonding the polymerizable ligand to the CNTs.
10. A method for providing a polymerizable functionality to carbon
nanotubes (CNTs), the method comprising the step of non-covalently
bonding vinylanthracene to the sidewalls of the CNTs.
11. A polymer-nanotube composite comprising: carbon nanotubes
(CNTs) functionalized by having a polymerizable ligand
non-covalently bonded thereto; and a polymer bound to the
functionalized CNTs.
12. The polymer-nanotube composite as recited in claim 11, wherein
the functionalized CNTs are dispersed throughout the polymer.
13. The polymer-nanotube composite as recited in claim 12, wherein
the polymer is nylon.
14. The polymer-nanotube composite as recited in claim 11, wherein
the polymerizable ligand comprises a polyaromatic molecule with a
polymerizable group attached thereto.
15. The polymer-nanotube composite as recited in claim 14, wherein
the polyaromatic molecule comprises a polyaromatic hydrocarbon.
16. The polymer-nanotube composite as recited in claim 15, wherein
the polyaromatic hydrocarbon comprises anthracene.
17. The polymer-nanotube composite as recited in claim 14, wherein
the polymerizable group comprises one of a styryl group or a vinyl
group.
18. The polymer-nanotube composite as recited in claim 11, wherein
the polymerizable ligand comprises vinylanthracene.
19. The polymer-nanotube composite as recited in claim 11, wherein
the polymerizable ligand is bonded to the sidewalls of the
CNTs.
20. The polymer-nanotube composite as recited in claim 11, wherein
the polymerizable ligand is also bonded covalently to the CNTs.
21. A polymer-nanotube composite comprising: carbon nanotubes
(CNTs) functionalized by having vinylanthracene non-covalently
bonded to the sidewalls thereof; and nylon bound to the
functionalized CNTs.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of prior filed,
co-pending U.S. provisional application: Ser. No. 60/823,769, filed
on Aug. 29, 2006, which is hereby incorporated by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates generally to functionalizing
nanotubes to form improved polymer-nanotube composites and, more
particularly, to a method for functionalizing carbon nanotubes with
a polymerizable ligand formed using polymerizable groups, for
example, vinyl or styryl groups, in combination with a polyaromatic
molecule such as a polyaromatic hydrocarbon (PAH) for the purpose
of achieving significant improvements in the properties of a
polymer-nanotube composite due to improved dispersion and chemical
bonding between the polymer matrix and the nanotube itself.
[0005] 2. Description of Related Art
[0006] Sustaining habitation on the moon, or any other planet, will
require light weight, high strength structures that protect against
both radiation and particulates. Chemical synthesis techniques to
enable strong bonding between carbon nanotubes and polymers to form
improved polymer-nanotube composites, technology which could be
used for this application, are needed.
[0007] Polymer properties such as electrical conductivity have been
shown to be enhanced by incorporating therein a combination of
carbon fibers or carbon nanotubes (CNTs). Additionally, CNTs have
been shown to prevent delamination and provide structural stability
in polymer composites. Because CNTs have uniquely high strength to
mass ratio, intrinsic light weight, thermal conductivity,
electrical conductivity, and chemical functionality, and, as noted,
have been shown to prevent delamination and provide structural
stability in polymer composites, they can impart these properties
to polymers when effectively combined therewith.
[0008] Though CNTs have extraordinary mechanical properties, their
ability to strengthen polymers and epoxies is limited by the
strength of interfacial bonding. As a result, when incorporated
into polymeric resin without cross-linking or functionalization,
they lack the ability to transfer loads across the structure.
[0009] CNTs can be functionalized via covalent or non-covalent
bonding, to either the ends of the nanotubes or to the sidewalls.
Covalent functionalization often requires beginning with modified
tubes, such as fluorinated nanotubes, or with purified tubes where
defect sites in the CNTs are produced by oxidation. Because these
modifications often result in the disruption of the bonds along the
tubes themselves, covalent functionalization can degrade the
mechanical and electrical properties of the nanotubes and, thus, is
not ideal for all applications.
[0010] Therefore, the present invention has been made in view of
the above problems, and it is an objective of the present invention
to provide a method for functionalizing carbon nanotubes using
polymerizable ligands and to form improved polymer-nanotube
composites utilizing the functionalized nanotubes.
SUMMARY OF THE INVENTION
[0011] Non-covalent functionalization to the sidewalls of CNTs can
be attained by exploiting the van der Waals and pi-pi bonding
between the pi electrons of the CNTs and that of a polyaromatic
molecule, for example, a polyaromatic hydrocarbon (PAH) such as
anthracene. This type of functionalization results in higher
degrees of functionalization as the entire length of the CNT can be
functionalized rather than just the ends and specific active sites.
Like end-functionalization, non-covalent functionalization also
opens up the possibility for tailoring the functionalization via
the choice of molecule.
[0012] For the purpose of polymerizing the CNT to a polymer resin
or epoxy, in one embodiment, a polymerizable ligand comprising a
polyaromatic molecule such as PAH with an appropriate polymerizable
group such as a vinyl, styryl, or amino group can be non-covalently
bonded to the CNTs. In the embodiment shown in FIG. 1,
single-walled carbon nanotubes (SWNTs) are functionalized with a
polymerizable ligand, vinylanthracene, thereby enabling improved
crosslinking or bonding and dispersion of CNTs into a polymer. This
results in improving the mechanical properties of the interface
between the CNTs and the polymer thereby imparting many of the
valuable properties of CNTs into the polymer matrix resulting in a
significantly improved polymer-nanotube composite.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] These and other objects, features and advantages of the
invention will be apparent from a consideration of the following
Detailed Description considered in conjunction with the drawing
Figures, in which:
[0014] FIG. 1 is a schematic of a SWNT functionalized with
vinylanthracene.
[0015] FIG. 2 is a graph illustrating the absorption spectra of
SWNT solution before and after functionalization with
vinylanthracene.
[0016] FIG. 3 is a graph illustrating fluorescence spectra of
purified SWNTs, vinylanthracene alone, and vinylanthracene
functionalized SWNTs.
[0017] FIG. 4 is a scanning electron microscope (SEM) image of
nylon 12 with approximately 1% by weight of purified but
non-functionalized multi-walled carbon nanotubes (MWNTs).
[0018] FIG. 5 is an SEM image of nylon 12 approximately 1% by
weight of purified but non-functionalized MWNTs.
[0019] FIG. 6 is an SEM image of nylon 12 approximately 1% by
weight of vinylanthracene-functionalized MWNTs.
[0020] FIG. 7 is an SEM image of nylon 12 with approximately 1% by
weight of vinylanthracene-functionalized MWNTs.
[0021] FIG. 8 is an SEM image of nylon 12 with approximately 1% by
weight of vinylanthracene-functionalized MWNTs.
DETAILED DESCRIPTION
[0022] In a first set of experiments, the CNTs were SWNTs produced
by the HipCO method and purified by refluxing in 3M HNO.sub.3 for
16 hours. To functionalized the nanotubes, a mixture of CNTs and
vinylanthracene, at a ratio of 1:2 by weight, were sonicated for
approximately one hour in dry tetrahydrofuran (THF). To remove
unreacted vinylanthracene, CNTs were collected by filtration,
washed with THF, and dried over vacuum in air. Absorbance and
fluorescence data were collected as evidence of
functionalization.
[0023] The CNTs in the second set of experiments were MWNTs
purified in 3M HNO.sub.3 for 4 hours. A shorter reflux time was
chosen to preserve longer length tubes. To functionalize the
nanotubes, a mixture of CNTs and the appropriate anthracene
derivative, at a ratio of 2:5 by weight, were mixed in THF for 72
hours. To remove unreacted ligand, CNTs were collected by
filtration, washed with THF, and dried over vacuum in air.
Fluorescence data was collected as evidence of
functionalization.
[0024] In situ synthesis of nylon 12 was completed in solution,
based on the Haggenmueller method for nylon 6. A solution of
0.0325M diaminododecane was prepared by stirring for 24 hours in
chloroform, solution A. A solution of dodecanedioyl chloride in
toluene was prepared at three times the concentration, 0.0975M,
solution B. To prepare a batch of Nylon 12, 300 mL of Solution A
were placed in a 600 mL beaker and stirred with an overhead stirrer
at 230 rpm for about one minute. If appropriate, CNTs from above
were ground with mortar and pestle, and then added to the beaker.
Finally, 100 mL of solution B were added and left to stir for 30
minutes. The nylon produced was collected with a glass frit filter,
washed with toluene and chloroform, and dried over vacuum in air.
Typical yields were about 85%.
[0025] Nylon produced from the in situ methods was analyzed by
scanning electron microscope (SEM). The polymer was overcoated with
gold to improve the quality of the images recorded. The SEM used
was Hitachi S-4700 Cold Field Emission Scanning Electron Microscope
(FE-SEM). Images were recorded at 5 kV at short working distances
around 5 to 6 mm.
[0026] Electronic structure of carbon nanotubes is dominated by van
Hove singularities which give rise to distinct peaks in the density
of states as seen by I/V measurements. The first electronic
transition in metallic carbon nanotubes is denoted M.sub.11 and the
first and second electronic transitions in semiconducting carbon
nanotubes are denoted S.sub.11 and S.sub.22, respectively. These
transitions typically correspond to absorbances in the visible and
near infrared wavelengths. Absorption spectra of solution-phase
carbon nanotube suspensions typically exhibit all of these features
due to the presence of all types of CNTs in solution. Chemical
affinity-induced separation of metallic from semiconducting
nanotubes via functionalization and centrifugation has been tracked
via these resonances, as has chemical doping resulting in
disruption of the electronic structure of the CNTs. Changes in
these resonances were used to observe changes in electronic
structure resulting from functionalization with
vinylanthracene.
[0027] Surface modification has been shown to affect the S.sub.11
and S.sub.22 electronic transitions in carbon nanotubes. A solution
having molarity 2.times.10.sup.-3M of purified unfunctionalized
nanotubes (background substracted for 1% wt. Triton X-100 in THF)
exhibited broad peaks characteristic of solution-phase S.sub.11 and
S.sub.22 level transitions. Functionalized nanotube solution
exhibited no such peaks within the same range of wavelengths, as
shown in FIG. 2. This diminished S.sub.11 peak intensity after
non-covalent functionalization of nanotube sidewalls is known in
the literature. It is thought that complexation in this manner may
change the electronic density of states of the nanotube. Similarly
functionalized SWNTs have been compared to highly defective
double-walled nanotubes having significantly different density of
states from a pristine SWNT.
[0028] In addition to changes in the absorption spectra,
functionalization of carbon nanotubes can be observed through
changes in fluorescence before and after functionalization,
particularly when the ligand or attached group is fluorescent. This
is the case with vinylanthracene, which fluoresces strongly at
.about.400-420 nm when excited at 350 nm, as shown in FIG. 3. The
SWNTs used in these experiments did not have any overlapping
fluorescence in this region, thus the presence of vinylanthracene
fluorescence peaks in a well-rinsed and purified functionalized
SWNT sample is indicative of functionalization. Fluorescence
spectra of purified SWNTs prior to functionalization with
vinylanthracene, of vinylanthracene in solution, and of
vinylanthracene-functionalized SWNTs are shown in FIG. 3.
[0029] Precipitated CNTs were removed from filter paper after
washing and suspended in heptane. Heptane was selected because it
is a dry solvent that does not have any fluorescent or Raman peaks
near those of vinylanthracene. Emission spectrum of this solution
and of a 2.times.10.sup.-4M standard of vinylanthracene in heptane
were recorded. The wavelengths of the fluorescence peaks were very
similar in the two cases. Peaks appeared at 404 and 423 nm for the
unbound vinylanthracene, and at 403 and 422 nm for the filtrate
solution. By contrast, the relative heights of the peaks shifted
somewhat; in the standard sample, the peak at 422 nm is higher than
that at 403 nm, while the peaks are approximately equal in height
for the functionalized CNTs. This difference may be the result of a
slight fluorescence quenching due to energy transfer between the
bound vinylanthracene and CNT wall.
[0030] A series of standards of vinylanthracene were used to create
a calibration curve. The estimated concentration of CNT-bound
vinylanthracene using this calibration curve is approximately
3.2.times.10.sup.-6M. The number of vinylanthracene molecules per
SWNT can be computed if the average molecular weight of a carbon
nanotube is known. For these calculations, the weight of the CNTs
was estimated by assuming an average bond length of 0.32 nm, a tube
diameter of 0.7 nm, and tube lengths between 1 and 10 nm. Assuming
the average molecular weight of a carbon nanotube is 2,242,800
g/mol, the ratio is roughly estimated to be about 143 molecules of
vinylanthracene per nanotube. A similar set of fluorescence
experiments was completed to confirm the functionalization of MWNTs
with vinylanthracene.
[0031] Scanning electron microscopy (SEM) was used to image nylon
that was produced by the in situ process in order to determine how
well the CNTs were dispersed throughout the polymer. It is critical
that the CNTs be well dispersed in order to maximize their effect
on the material's mechanical and rheologic properties. If the tubes
are clumped together, then large regions of the polymer substrate
will insulate the tubes, and the overall thermal and electrical
conductivity will be low. In addition, evidence of good dispersion
may indicate that the polymer is chemically bonding to the
functional groups along the CNTs. It has been suggested that CNTs
which are dispersed within a polymer but not chemically bound to
it, can rotate or shift, and therefore do not effectively resist
strain applied to the material. Creating a physical bond directly
between the polymer and the CNTs or its functional groups, should
increase the modulus of the bulk material.
[0032] The nylon 12 polymer in FIGS. 4-8 was made by the in situ
method described above. Purified MWNTs were added to the first
batch at about 1% by weight, assuming a 100% yield of polymer. The
second batch of nylon was made with the same percentage of MWNTs,
however these tubes were functionalized with vinylanthracene. As
shown in FIGS. 4 and 5, it is obvious that the non-functionalized
tubes are collected in a single large clump which is surrounded
entirely by polymer. However, the functionalized CNTs in the second
batch appear in FIG. 6 to be dispersed throughout the polymer. At
the 1 micron scale in FIG. 7, it is possible to see individual
tubes separated from one another by nylon polymer.
[0033] In the FIG. 8, there are small nodules of material that
appear to be placed along the length of a long tube. This image
indicates beads of nylon 12 growing at reactive sites along the
CNT. The reactive sites can include defects in the CNT itself,
including carboxylic acid sites, or non-covalently attached
functional groups.
[0034] CNTs functionalized with vinylanthracene appear to aid in
the dispersion of MWNTs through the nylon 12 polymer matrix. Though
not directly involved in the chemical reaction between the amine
and the dioyl chloride of the polymer, the vinyl group may interact
with the polymer as well. The electron cloud surrounding the double
bond of the vinyl group may share some electron density with the pi
electrons in the amide link of the polymer. The location of the
vinyl group, hanging off of the anthracene molecule with little
steric interference from other bonds, may increase the likelihood
that the CNT becomes entangled in the polymer matrix.
[0035] The polymerization of MWNTs with nylon 12 where the MWNTs
have been functionalized with different anthracene derivatives is
also possible. Candidates include diamino anthracene or dioyl
chloride anthracene. In general, however, materials containing
functionalized CNTs will see significant improvements due to
improved dispersion and the chemical bonding between the polymer
matrix and the nanotube itself.
[0036] As noted above, the chemical synthesis techniques of the
present invention enable strong bonding between carbon nanotubes
and polymers, resulting in polymer-nanotube composites with
improved polymer properties. These properties include, but are not
limited to, improved electrical conductivity, thermal conductivity,
mechanical strength.
[0037] The polymer-nanotube composites of the present invention may
be used, for example, as thermoplastics, thermosets and conductive
fillers. These materials may, for example, be used to protect
sensitive electronic devices against the threat of electrostatic
discharge and electromagnetic or radio frequency (RF) interference.
In addition, these materials may be used to create paint that is
applied, for example, to the walls of homes, commercial properties,
or automobile body parts. The polymer-nanotube composites of the
present invention may be used to create electrostatic materials,
electromagnetic shielding, active electronics, printed circuit
boards or conducting adhesives
[0038] The methods of the present invention may be used to create
biocompatible carbon-nanotube polymers. The methods of the present
invention may be used to create carbon-nanotube polymers that are
incorporated into plastic chips, a wide variety of consumer
products, or electronic devices. The methods of the present
invention may be used to create carbon-nanotube polymers that are
incorporated into rechargeable batteries, solid ectrolytes,
electrical displays, photovoltaics, actuators, switches, sensors
(for example, chemical, biochemical or thermal sensors), or smart
structures.
[0039] The methods of the present invention may be used to create
light weight, high strength structures. These structures may, for
example, protect against radiation and particulates. Light weight,
high strength structures created according to the methods of the
present invention may be used, for example, to create vehicles,
including aircraft and spacecraft, as well as sustaining
habitation, hospitals, or other buildings on the moon, earth, or
any other planet.
[0040] While various embodiments have been described above, it
should be understood that they have been presented by way of
example only, and not limitation. Thus, the breadth and scope of a
preferred embodiment should not be limited by any of the above
described exemplary embodiments, but should be defined only in
accordance with the following claims and their equivalents.
* * * * *