U.S. patent application number 11/467745 was filed with the patent office on 2007-05-17 for methods for processing multifunctional, radiation tolerant nanotube-polymer structure composites.
Invention is credited to Marwan S. Al-Haik, Mohamed S. El-Genk.
Application Number | 20070110977 11/467745 |
Document ID | / |
Family ID | 38041186 |
Filed Date | 2007-05-17 |
United States Patent
Application |
20070110977 |
Kind Code |
A1 |
Al-Haik; Marwan S. ; et
al. |
May 17, 2007 |
METHODS FOR PROCESSING MULTIFUNCTIONAL, RADIATION TOLERANT
NANOTUBE-POLYMER STRUCTURE COMPOSITES
Abstract
Embodiments provide a composite material with oriented nanotubes
and a method for making the composite material. The composite
material can be formed by distributing a plurality of nanotubes in
a polymer matrix. The nanotubes can be further magnetically
oriented during the formation of the polymeric matrix, while the
polymer matrix is magnetically annealed. The composite material can
provide enhanced mechanical and electrical properties, and
effective radiation resistance against high-energy ionizing
radiation particles and/or electromagnetic interferences. The
composite material can be useful for lightweight armors
incorporated into vehicles, aircrafts or personnel protection with
high ballistic properties, and efficient dissipation of radiation
energies, photovoltaic cells with improved polymer solar cell
efficiency, improved light emitting diodes (LEDs) with controllable
optical properties, or infrared screening devices with increased
extinction coefficient.
Inventors: |
Al-Haik; Marwan S.;
(Albuquerque, NM) ; El-Genk; Mohamed S.;
(Albuquerque, NM) |
Correspondence
Address: |
MH2 TECHNOLOGY LAW GROUP
1951 KIDWELL DRIVE
SUITE 550
TYSONS CORNER
VA
22182
US
|
Family ID: |
38041186 |
Appl. No.: |
11/467745 |
Filed: |
August 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60711678 |
Aug 29, 2005 |
|
|
|
60726652 |
Oct 17, 2005 |
|
|
|
Current U.S.
Class: |
428/292.1 |
Current CPC
Class: |
F41H 5/02 20130101; Y10T
428/249924 20150401; B29K 2105/167 20130101; B29C 70/62 20130101;
F41H 5/04 20130101; F41H 5/0492 20130101; C08K 7/00 20130101; C08K
7/00 20130101; C08L 25/00 20130101 |
Class at
Publication: |
428/292.1 |
International
Class: |
D04H 13/00 20060101
D04H013/00 |
Claims
1. A composite material formed by the steps comprising: providing a
plurality of nanotubes; distributing the plurality of nanotubes in
one of a resin and a hardener to form a first mixture; forming a
second mixture by combining the other of the resin and the hardener
with the first mixture; degassing the second mixture; and curing
the second mixture under a magnetic field of about 15 Tesla or more
to orient the plurality of nanotubes.
2. The composite material of claim 1, wherein the plurality of
nanotubes comprise nanofibers.
3. The composite material of claim 1, wherein the plurality of
nanotubes comprise carbon nanotubes, wherein the carbon nanotubes
comprise one of single wall carbon nanotubes (SWCNs) or multi-wall
carbon nanotubes.
4. The composite material of claim 3, wherein the SWCNs comprise
armchair type nanotubes having a chirality where n=m.
5. The composite material of claim 1, wherein a weight percentage
of the plurality of is 35% or less of the composite material.
6. The composite material of claim 1, wherein the resin and the
hardener form an epoxy with low viscosity at room temperature.
7. The composite material of claim 1, wherein the plurality of
nanotubes are oriented anisotropically.
8. A ballistic resistant material comprising the composite material
of claim 1, wherein the plurality of nanotubes are aligned
co-axially to a line of impact.
9. A ballistic resistant material comprising the composite material
of claim 1, wherein the plurality of nanotubes are aligned
orthogonally to a line of fire or a line of impact.
10. A ballistic resistant material comprising the composite
material of claim 1 further comprising at least one of boron
carbide and silicon carbide.
11. The composite material of claim 1 further comprising at least
one form of a film, sheet, fiber, cylinder, foam, coating or
paste.
12. A method for making a composite material comprising: providing
a plurality of carbon nanotubes; distributing the plurality of
carbon nanotubes in a hardener; forming a mixture by combining a
resin with the hardener and the plurality of carbon nanotubes;
degassing the mixture; and curing the mixture under a magnetic
field of about 15 Tesla or more to align the plurality of
nanotubes.
13. The method of claim 12 further comprising: adding a first
solvent to the plurality of carbon nanotubes, wherein the first
solvent comprises an ethanol; adding a second solvent to the resin,
wherein the second solvent comprises an ethanol; and combining the
first solvent and the plurality of carbon nanotubes with the second
solvent and the resin.
14. The method of claim 12, wherein providing the plurality of
carbon nanotubes comprises purifying the carbon nanotubes.
15. The method of claim 12 further comprising providing a solvent
for steps of providing carbon nanotubes and distributing the carbon
nanotubes in the hardener, wherein the solvent comprises an
ethanol.
16. The method of claim 12 further comprising placing the carbon
nanotubes distributed hardener in a vacuum at about 60.degree. C.
or more for at least one hour.
17. The method of claim 12 further comprising stirring the mixture
at about 2000 rpm or more for at least 5 minutes prior to the step
of curing.
18. The method of claim 12, wherein curing the mixture comprises:
curing the mixture at room temperature for at least two hours under
the magnetic field; curing the mixture at about 60.degree. C. or
more for at least two hours under the magnetic field; and curing
the mixture at about 60.degree. C. or more for at least two hours
under no magnetic field.
19. A composite material comprising: a polymer matrix, wherein the
polymer comprises at least one of a thermosetting polymer and a
thermoplastic polymer; and a plurality of nanotubes distributed in
the polymer matrix, wherein the plurality of nanotubes are
magnetically aligned during formation of the polymeric matrix.
20. A ballistic resistant material comprising the composite
material of claim 19, wherein the plurality of nanotubes are
aligned co-axially to a line of impact.
Description
RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Patent Applications Ser. No. 60/711,678, filed Aug. 29, 2005, and
Ser. No. 60/726,652, filed Oct. 17, 2005, which are hereby
incorporated by reference in their entirety.
FIELD OF THE INVENTION
[0002] This invention relates generally to composite materials and,
more particularly, to composite materials with magnetically
oriented nanotubes in a polymer matrix.
BACKGROUND OF THE INVENTIONS
[0003] Organic materials such as polymers offer an attractive route
for a wide variety of applications, such as armor devices,
photovoltaic devices, light emitting diodes (LEDs), or infrared
screening devices, due to their advantages of lightweight (i.e.
mass-effective), low cost, ease of fabrication, and flexibility.
For example, polymers used as protective armor materials against
low-level of threats (e.g., NIJ level III or lower) offer the
distinctive advantage of lower density over materials such as
metals or ceramics. However, because of their relatively low
strength and hardness, polymers are commonly reinforced with either
organic or ceramic fibers/whiskers, and are used in conjunction
with harder metals and ceramics when they are used in protective
systems against higher level of threats, such as NIJ Level IV or
higher. An example is standard body armor where a ceramic armor
plate is combined with Kevlar.TM. (a type of polymeric synthetic
fiber from DuPont Company (Wilmington, Del.)) and graphite fiber in
a polyurethane and urea matrix to provide sufficient protection. In
another example, polymers may be used as infrared screening films
since conventional armor materials such as metal alloy brass are
highly toxic. However, problems arise due to the low electrical
conductivity for most polymers.
[0004] Carbon nanotubes possess exceptional mechanical properties
and superior electric and thermal properties and can be used as
reinforcement fibers for structural composites. For example, a cast
composite film consisting of polystyrene and randomly oriented
carbon nanotubes (5% volume fraction) has been shown to increase
the specific modulus by 100% and the strength of the polystyrene by
25%. In addition, carbon nanotube reinforcement can increase the
toughness of the composite by absorbing energy because of its high
elastic behavior during loading. Furthermore, carbon nanotubes are
environmental friendly compared with materials such as brass in
conventional infrared screening devices.
[0005] Therefore, it is desirable to combine carbon nanotubes with
polymers to provide distinctive properties. Limitations arise,
however, because utilizing the unique properties of carbon
nanotubes depends on the spatial control and dispersion of
individual nanotubes in the polymer matrix, and on the interaction
between the polymer and the nanotubes, such as, the ability to
transfer load from the matrix to the nanotubes.
[0006] Thus, there is a need to overcome these and other problems
of the prior art and to provide a controlled processing of
nanotubes with polymer matrix forming a composite material with
oriented nanotubes.
SUMMARY OF THE INVENTION
[0007] According to various embodiments, the present teachings
include a composite material with magnetically oriented nanotubes.
To form the composite material, a plurality of nanotubes are
distributed in one of a resin and a hardener to form a first
mixture. A second mixture is then formed by combining the other of
the resin and the hardener with the first mixture. The second
mixture is then degassed and cured under a magnetic field of about
15 Tesla or more to orient the nanatubes.
[0008] According to various embodiments, the present teachings
further include a composite material including a polymer matrix
with distributed nanotubes. The polymer matrix includes at least
one of thermosetting polymers or thermoplastic polymers. The
nanotubes are magnetically aligned during formation of the
polymeric matrix.
[0009] Additional objects and advantages of the invention will be
set forth in part in the description which follows, and in part
will be obvious from the description, or may be learned by practice
of the invention. The objects and advantages of the invention will
be realized and attained by means of the elements and combinations
particularly pointed out in the appended claims.
[0010] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the invention, as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate several
embodiments of the invention and together with the description,
serve to explain the principles of the invention.
[0012] FIG. 1 is a block diagram of an exemplary method for making
a composite material in accordance with the present teachings.
[0013] FIG. 2 is a schematic diagram for an exemplary magnetically
aligned composite material 200 in accordance with the present
teachings.
[0014] FIG. 3 depicts an exemplary armor device 300 providing
protection from projectile threats in accordance with the present
teachings.
[0015] FIG. 4 depicts an exemplary method for resisting ionizing
radiations with composite armor material in accordance with the
present teachings.
DESCRIPTION OF THE EMBODIMENTS
[0016] Embodiments provide a composite material including oriented
nanotubes and a method for making the composite material. The
composite material may be formed by distributing a plurality of
nanotubes in a polymer matrix. The nanotubes may be further
magnetically oriented during curing of the polymeric matrix. The
composite material may provide enhanced mechanical and electrical
properties, and effective radiation resistance against high-energy
ionizing radiation particles and/or electromagnetic interferences.
The composite material can be useful for many applications
including, but not limited to, armors for vehicles, aircrafts and
personnel protection, with high ballistic properties, and efficient
dissipation of radiation energies, photovoltaic devices with
improved polymer solar cell efficiency, improved LEDs with
controllable optical properties, and infrared screening devices
with increased extinction coefficient.
[0017] Reference will now be made in detail to exemplary
embodiments of the invention, an example of which is illustrated in
the accompanying drawings. Wherever possible, the same reference
numbers will be used throughout the drawings to refer to the same
or like parts.
[0018] In the following description, reference is made to the
accompanying drawings that form a part thereof, and in which is
shown by way of illustration specific exemplary embodiments in
which the invention may be practiced. These embodiments are
described in sufficient detail to enable those skilled in the art
to practice the invention and it is to be understood that other
embodiments may be utilized and that changes may be made without
departing from the scope of the invention. The following
description is, therefore, merely exemplary.
[0019] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations;
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical value, however,
inherently contains certain errors necessarily resulting from the
standard deviation found in their respective testing measurements.
Moreover, all ranges disclosed herein are to be understood to
encompass any and all sub-ranges subsumed therein. For example, a
range of "less than 10" can include any and all sub-ranges between
(and including) the minimum value of zero and the maximum value of
10, that is, any and all sub-ranges having a minimum value of equal
to or greater than zero and a maximum value of equal to or less
than 10, e.g., 1 to 5.
[0020] As used herein, the term "nanotube" refers to any
cylindrical shaped material (including organic or inorganic
material) with a diameter of about 100 nanometers or less. The term
"nanotubes" also refers to single wall nanotubes, multiwall
nanotubes, and their various functionalized and derivatized fibril
forms, which include nanofibers. The nanofibers can be fibrils with
diameters of 100 nm or less in at least one form of thread, yarn,
fabrics, etc.
[0021] FIG. 1 shows a block diagram of an exemplary method for
forming a composite material in accordance with the present
teachings. It should be readily obvious to one of ordinary skill in
the art that the method depicted in FIG. 1 represents a generalized
schematic illustration and that other steps may be added or
existing steps may be removed or modified.
[0022] As shown in FIG. 1, at 110, a plurality of nanotubes may be
provided. In various embodiments, the provided nanotubes may be
carbon nanotubes, which may include but are not limited to single
wall carbon nanotubes (SWCNs) or multi-wall carbon nanotubes. In
some embodiments, the SWCNs may be armchair type nanotubes
(n,n).
[0023] In various embodiments, the nanotubes may be obtained in low
and high purity dried paper forms or may be purchased in various
solutions. The nanotubes may also be available in the as-processed,
unpurified condition, which may carry with them numerous unwanted
impurities that may affect composite properties. Accordingly, at
110, the plurality of nanotubes may be provided from a purification
process, which utilizes ultrasonically assisted filtrations. The
ultrasonic energy source may be, for example, a high-intensity
ultrasonic processor. In the purification process, for example, the
nanotubes can be ultrasonically suspended in a first solvent, such
as, toluene, and then filtered to extract the soluble fullerenes
leaving an insoluble fraction. The insoluble fraction may then be
ultrasonically re-suspended in a second solvent, such as a
methanol, and transferred in a filtration funnel configured with a
filter membrane. A pressure differential of, for example, about 50
Torr, may be applied across the filter membrane. The filter
membrane may be, for example, a polycarbonate track-etched filter
membrane with a pore size of about 0.8 .mu.m. The obtained
nanotubes may then be washed with a third solvent, such as a
sulfuric acid with an exemplary concentration of 6 M, to remove
traces of metal such as titanium introduced into the sample from
the ultrasonic horn.
[0024] At 120 of FIG. 1, a plurality of nanotubes can be
distributed in a resin. Distributing nanotubes in a resin may
further include first dispersing nanotubes in a solvent, such as an
ethanol, and then ultrasonically mixing nanotube-ethanol, for
example, at about 10% amplitude for about 90 seconds using the
high-intensity ultrasonic processor. Meanwhile, the resin may also
be ultrasonically mixed with ethanol at about 10% amplitude for
about 90 seconds. The nanotubes/ethanol mixture may then be
combined with the resin/ethanol mixture and ultrasonically mixed at
about 50% amplitude for about 90 seconds. This process may promote
the distribution of nanotubes over the surface of the resin
molecules and prevent nanotube clustering. The exemplary embodiment
described herein utilizes a polymer matrix formed of DERAKANE
411-350 epoxy vinyl ester resin manufactured by Ashland Inc.
(Covington, Ky.).
[0025] Still at 120 of FIG. 1, to form the composite material, a
designated weight fraction of purified nanotubes, such as, for
example, 35% or less by weight, may be dispersed in a hardener part
of an epoxy by first dispersing the plurality of nanotubes in a
solvent such as ethanol in an ultrasonic bath at room temperature
for about one hour. Then the ethanol-based nanotube solution may be
mixed with the hardener and the mixture may be stirred for at least
one hour at about 2000 rpm or more. During this stirring process,
the nanotube-hardener mixture may be kept at room temperature to
maintain a low viscosity using a silicon oil bath for example. In
various embodiments, the solvent ethanol may be removed by
evaporation where the mixtures may be placed in a vacuum oven at
about 60.degree. C. or more for at least one hour.
[0026] At 130 of FIG. 1, a resin part of the epoxy may then be
added to the nanotube-hardener mixture to form a composite mixture
with a desired resin/hardener ratio, such as 4:1 by weight. The
epoxy may include, but are not limited to, one or more of aeropoxy,
thixotropic epoxy, Derakane-441, or other type of epoxy. The
composite mixture may be stirred at about 2000 rpm or more for at
least 5 minutes.
[0027] At 140 of FIG. 1, the composite mixture may be degassed
moderately until no gas bubbles can be seen. The degassed mixture
may then be loaded into molds of a desired shape which may result
in a variety of 3-D structures for the nanotube-polymer composite,
such as, for example, a sheet, a fiber, a cylinder, a foam or other
3-D structure. The molds may be sealed for a subsequent magnetic
process. In various embodiments, the degassed composite mixture may
be formulated as a film or coated on various substrates and then be
loaded for a subsequent magnetic process.
[0028] At 150 of FIG. 1, the composite mixture may be cured at room
temperature with a low viscosity under a high magnetic field, such
as 15 Tesla or more for at least 2 hours. Then, still under the
high magnetic field, the curing temperature may be increased up to
about 60.degree. C. or more for also at least 2 hours. During the
magnetic process, the polymer may be annealed and the nanotubes may
be oriented in the polymer matrix (i.e. the curing mixture of the
resin and the hardener of the epoxy in this example) due to the
cooperative effect of the magnetic torque exerted by the magnetic
field directly on the nanotubes and by hydrodynamic torque and
viscous shear (i.e. drag forces) exerted on the nanotubes by the
polymer chains. In addition, the magnetic field may be penetrable
and its direction and strength may be controllable. Accordingly,
the alignment of the nanotubes may be controlled for desired
orientation(s) depending on specific applications. More
specifically, the alignment profile may be specially designed for
desired enhanced properties of the composite material, such as
enhanced mechanical and electrical properties, or efficient
radiation resistance.
[0029] Turning to 150 of FIG.1, the magnetic field may then be
removed and the composite mixture may remain cured at about
60.degree. C. or more for at least 2 hours to fully cure the
polymer matrix, i.e., the resin and the hardener of the epoxy in
this example. One of ordinary skill in the art will understand that
other polymers may be also used for the polymer matrix including
but not limited to thermosetting polymers and thermoplastic
polymers. In various embodiments, boron carbide particles, silicon
carbide particles, or other similar hard materials may be
incorporated into the polymer matrix for the composite
material.
[0030] FIG. 2 shows a schematic diagram of an exemplary
magnetically oriented composite material 200 including a plurality
of nanotubes 210 and polymer fibrils 220 formed in accordance with
the present teachings. Arrow 230 indicates a direction of the
applied magnetic field. It should be readily obvious to one of
ordinary skill in the art that the exemplary magnetically oriented
composite material 200 depicted in FIG. 2 represents a generalized
schematic illustration and that more nanotubes or polymer fibrils
may be added or existing nanotubes or polymer fibrils may be
removed or modified.
[0031] As shown in FIG. 2, the plurality of nanotubes 210 can be
oriented in a direction parallel to the magnetic field indicated by
the arrow 230. In some embodiments, the nanotubes 210 may be
magnetically oriented single wall carbon nanotubes (SWCNs). In
other embodiments, the nanotubes 210 may be locally oriented, for
example, through a mechanical stretching, or a pressing through a
die or electric field. As a result, the composite material 200 with
locally oriented nanotubes may provide specially-varying mechanical
properties for specific applications, such as, for example, a
composite tube with strong exterior and soft interior.
[0032] The polymer fibrils 220 may be uniform along the direction
of the magnetic field indicated by the arrow 230. When a magnetic
field is applied during the formation of the polymer, such as, for
example, during the curing of a liquid epoxy, the polymer molecules
may also be annealed (e.g., aligned) along the direction of the
applied magnetic field and taking fibril shape. Accordingly, the
polymer fibrils 210 may be magnetically aligned epoxy fibrils in
accordance with various embodiments.
[0033] In various embodiments, the magnetically oriented composite
material 200 may provide enhanced mechanical and electrical
properties. The enhanced mechanical properties may be demonstrated
by a specific strength and a specific modulus. The specific
strength (or modulus) may be determined by a material strength (or
modulus) divided by its density (e.g;, weight per unit volume). For
example, the magnetically oriented composite material 200 may
provide a specific strength of such as about 20 GPacm.sup.2/g to
about 50 GPacm.sup.2/g and a specific modulus of such as about 100
GPacm.sup.2/g to about 200 GPacm.sup.2/g.
[0034] The enhanced electrical properties for the magnetically
oriented composite material 200 may be demonstrated by the
electrical conductivity, such as, for example, an electrical
conductivity of about 10.sup.6 scm.sup.-1 or higher. Because of
this enhanced electrical conductivity, the magnetically oriented
nanotube-polymer composite material 200 may be used for, for
example, improved polymer-based light emitting diodes (LEDs),
especially when the polymer used is a photo-active polymer.
Compared with conventional LEDs, the nonotube-polymer based
composite material may be able to increase
photoluminescence/electro-luminescence yield, which may provide a
means to alter the optical properties of the polymer to tune the
color or emission for organic light emitting devices. One more
example for using the enhanced electrical conductivity of the
magnetically oriented nanotube-polymer composite material 200 may
be for infrared screening devices. The magnetically oriented
composite material 200 may be used as an environmental friendly
alternative to screen infrared radiations compared to highly toxic
materials that is conventionally in use such as brass. More
importantly, the enhanced electrical conductivity of the
magnetically oriented composite material 200 may increase the
extinction coefficient for infrared screening.
[0035] Accordingly, the magnetically oriented composite material
200 with enhanced mechanical and electrical properties may be used
for ballistic resistant material such as armor devices, that may be
as effective as steel against projectiles--at considerably lower
weight. FIG. 3 shows an illustration for an armor device 300 that
may provide protection from possible projectile threats in an
application of such as a ground combat vehicle. It should be
readily obvious to one of ordinary skill in the art that the armor
device 300 depicted in FIG. 3 represents a generalized schematic
illustration and that other layers may be added or existing layers
may be removed or modified.
[0036] In the armor device 300, the magnetically oriented composite
material 200 may be configured as armor interior 350. The armor
interior 350 may be overlaid by a layer 352 of metal, such as
aluminum, then a layer 354 of ceramic, such as alumina (i.e.,
aluminum oxide), and then a layer 356 of metal, such as steel. The
layer 352, 354, and 356 may be configured as an armor cover over
the armor interior 350.
[0037] To form the armor interior 350, the magnetically oriented
composite material 200 may undergo a scale up fabrication process
to meet specific applications. Accordingly, the resulting armor
interior 350 may be at least one form of films, sheets, fibers,
cylinders, foams, coatings or pastes.
[0038] As used for the armor interior 350, the nanotubes may be
magnetically oriented in certain directions with a high anisotropy
due to its one-dimensional structure. Such magnetic orientation of
nanotubes (including nanofibers) may be controlled to confer
specific properties to the armor interior 350. For example, by
rearranging the orientations of nanotubes, superior mechanical and
physical properties may be tailored to the armor interior 350. In
some embodiments, the oriented nanotubes in the armor interior 350
may be aligned co-axially with the line of fire to provide shear
load transfer in the frontal impact layer. In other embodiments,
the oriented nanotubes in the armor interior 350 may be aligned
orthogonally to the line of fire to provide tensile load support in
the structural baking layer.
[0039] In various embodiments, the magnetically oriented composite
material 200 may further be used as a shielding material and
provide effective radiation resistance against high-energy ionizing
radiation particles and/or electromagnetic interferences in
applications such as armor devices.
[0040] FIG. 4 depicts a method for resisting radiation including a
radiation source 410 and an armor device 420. The armor device 420
may include a composite armor material 430 enclosed in an armor
enclosure 440 formed with materials, such as aluminum. The
composite armor material 430 may include the magnetically oriented
composite material 200.
[0041] The radiation source 410 may provide ionizing particles,
electromagnetic interferences, or a combination of various
radiations. The ionizing particles may include alpha particles,
beta particles, gamma rays or x rays, cosmic ray or solar flares.
To measure the radiation resistance, the radiation source 410 may
provide radiations with high energy, such as, for example, an
ionizing particle with a proton beam for a radiation energy of 15
MeV (i.e. megaelectron volts) or higher. Alternatively, the
radiation source 410 may provide a proton beam with high
intensities, such as, ranging from the direct level of 109 beam
particles per second to 10 beam particles per second. Such high
energy radiation may be far more intense than would be expected in
a real environment, such as in space.
[0042] The armor device 420 may be exposed to the radiation source
410 to measure the radiation resistance of the composite armor
material 430. The radiation resistance may be demonstrated by a
shielding effectiveness (or attenuation fraction) that may be
measured. For example, when using a high-energy proton beam as
radiation source 410, the shielding effectiveness (or attenuation
fraction) may be measured in terms of the number of high-energy
particles in the beam before and after the proton beam hits the
shielding material, i.e. the magnetically oriented composite armor
material 430. The shielding effectiveness or attenuation fraction
for the composite armor material 430 may be, for example, about
0.60 or higher. In some embodiments, the composite armor material
430 may include magnetically aligned nanotubes with high aspect
ratio for providing enhanced transport properties for effective
electromagnetic interference shielding for electronics, which in
some cases may also need to be guarded against impact damages.
[0043] Generally, armor devices, such as, for example, the armor
device 300 in FIG. 3 or the armor device 420 in FIG. 4, may be
incorporated within vehicles, aircrafts or personnel armors to
provide lightweight protection against ballistic threats, enhanced
mechanical and electrical properties, and radiation protection
against high-energy ionizing particles and/or electromagnetic
interferences.
[0044] In various embodiments, the magnetically oriented composite
material 200 may also provide electronic properties based on
morphological modification or electronic interaction between the
two components, such as, for example, .pi.-conjugated polymers and
carbon nanotubes. In particular, the combination of carbon
nanotubes with .pi.-conjugated polymers may form an electronic
conjugation which may enable the polymers to be used as an active
material for photovoltaic devices, such as a photovoltaic cell. The
controlled magnetic processing of carbon nanotubes with
.pi.-conjugated polymers may improve the exciton dissociation and
carrier transport of the system and thus resulting in an improved
polymer solar cell efficiency.
[0045] Other embodiments of the invention will be apparent to those
skilled in the art from consideration of the specification and
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with a
true scope and spirit of the invention being indicated by the
following claims.
* * * * *