FIELD OF INVENTION
5
[001]
The present invention is related to the
preparation of conducting polymer
encapsulated
in
Multiwalled Carbon N
anotube
(MWCNT)
buckypaper
and
its
applicat
i
ons
.
More particularly the
present invention discloses
thin sheets of MWCNT/conducting polymer
which
can find
applications
in
shielding
of e
lectromagnetic interference in Ku
-
band
and
for dissipating
electrostatic charge.
10
BACKGROUND OF INVENTION
[002]
In current scenario,
Electrically conducting polymer
-
matrix composites have gained
popularity for electromagnetic interference shielding application
s because they are lightweight,
resistant to corrosion, and flexible and easily processed. These kinds of flexible conductive
15
composites may be used for typical antenna systems, lightning
-
protected aircraft composite
panels, avionics line replaceable unit
(LRU) enclosures, connector gaskets, electrostatic and
space charge dissipation materials, different types of electronic pressure sensitive switches or
sensors, and many other uses. These polymeric composites must be made conductive by
compounding them wit
h an electrically conducting filler, such as metal particles and filaments,
20
carbon particles (e.g., graphite and carbon black), and carbon fibers, in order to achieve the
required shielding effectiveness. For any filler, the EMI shielding effectiveness inc
reases with
increasing filler concentration in the composites, but the maximum filler loading is limited by the
poor composite mechanical properties at high filler loadings resulting from the poor filler
-
matrix
bonding. For materials and process cost savin
g and good mechanical properties, the attainment
25
of a high shielding effectiveness at a low filler loading is desirable.
[003]
With the development of powerful electronic and electrical equipments, EMI shielding
becomes
a
significant factor for proper functioning of equipments and in the prevention of
human health hazards. The materials generally used for shielding includes metals and metallic
composites. But they are associated with several disadvantages like
heavy weight
, corrosion, and
30
expensive processing techniques.
Conducting polymer coated multiwalled carbon nanotube
3
presents an alternative for EMI shielding because of lightweight,
anti
-
corrosion, excellent
conductivity and environmental stability.
[004]
Conducting polymer
coated multiwalled carbon nanotube buckypaper being
lightweight;
having
high electrical conductivity can be easily encapsulated within structures.
These exciting
features of conducting polymer coated multiwalled carbon nanotube buckypaper make it a strong
5
alternate to replace metal based EMI shielding and antistatic structures.
[005]
Following are the works done so far in the field of conductive polymers based materials
for protective EMI shielding:
[006]
US 20100188833A1
(
Electromagnetic interference shielding structure including
carbon nanotube or nanofiber films and methods
)
.
The patent relates to designing of a
10
composite material for electromagnetic interference shielding. The composite material comprises
a stack including at least two electrically conductive nanoscale fiber films, which are spaced
apart from one another by at least one insulating gap positioned
between the at least two
nanoscale fiber films. The stack is effective to provide a substantial multiple internal reflection
effect. An electromagnetic interference shielded apparatus and a method for shielding an
15
electrical circuit from electromagnetic in
terference is provided
.
[007]
US 6870092B2
(
Methods and apparatus for EMI shielding
)
In this patent details have
been given with respect to
methods and apparatus for improving the resiliency and airflow
through a honeycomb air vent filter while providing EMI shielding. In one embodiment, the
honeycomb can be manufactured from a dielectric (e.g., plastic) substrate to provide improved
20
resistan
ce to deformation as compared to conventional aluminum honeycomb. The dielectric
honeycomb substrate is metallized to provide EMI shielding capability. The metallized
honeycomb substrate is cut slightly oversize to fit an opening in an electronic enclosure
, which
results in elastic deformation of resilient perimeter spring fingers that are used to hold the
metallized dielectric honeycomb in place and provide electrical conductivity between the
25
metallized dielectric substrate and the enclosure, thereby elimi
nating the use of a frame. In
another embodiment, additional conductive layers can be added to the metallized dielectric
honeycomb. In yet another embodiment, the metallized dielectric honeycomb substrate can be
utilized in a framed configuration to provid
e improved durability.
[008]
CN103266542A
(
Preparation method of carbon nanotube electromagnetic wave shielding
30
paper
)
The invention relates to a method for preparing carbon nanotube electromagnetic wave
14
clearly observed from the figure that the contributions to the shielding effectiveness values
mainly come from the absorption rather than reflection mechanism.
O
n increasing the
concentration of PEDOT/PSS in the buckypaper the SE
A
increases linearl
y.
Example
5
[0043]
Antistatic
measurements of conducting polymer coated multiwalled carbon
5
nanotube buckypaper
The antistatic measurements of conducting polymer coated multiwalled carbon nanotube
buckypapers
were carried out by JCI 166v5 charge decay test unit. For antistatic properties
there are two set criteria to dissipate static charge from its surface; 1) criterion 1/e
–
measure
decay time of initial peak voltage to reach 1/e (37%) and 2) criterion 10% ‒
measure decay
10
time of initial peak voltage to reach 10%. For a material to be antistatic the decay time should
be less than half a second in the 1/e criterion and for 10% criterion the decay time should be
less than two seconds. Figure
9 shows the static
charge decay times of the PEDOT/CNT1,
PEDOT/CNT2, and PEDOT/CNT3 buckypapers measured by applying a positive potential of
5k V. From the figure it is observed that all three samples easily surpass the set criteria of 1/e
15
within 0.3 second and 10% within 0.
8 seconds which is due to the highly conducting nature of
the PEDOT/PSS and MWCNTs. Figure 9, show 1/e static charge decay time of
PEDOT/CNT1 buckypaper is 0.14 second whereas PEDOT
/
CNT2 and PEDOT/CNT3 shows
decay time of 0.15 and 0.24 second, respectively
,
is observed for PEDOTCNT3. Any material
showing static decay time less than 2 seconds is suitable for antistatic applications
.
20
[0044]
Table
I:
EMI shielding data of various combinations of PEDOT incorporated in MWCNT
matrix
. Test result.
Table 1
SI No.
Sample
PEDOT/PSS
MWCNTs
SE
T
SE
A
SE
R
1.
PEDOT/CNT1
0.013 g
0.25
31.73
19.94
11.79
2.
PEDOT/CNT2
0.026 g
0.25
52.17
35.79
16.38
3.
PEDOT/CNT3
0.065 g
0.25
55.11
42.66
12.45
[0045]
Microwave absorption behaviour of PEDOT/PSS coated MWCNTs bucky
papers were
25
investigated in the microwave frequency range of 12.4
-
18 GHz (Ku
-
band) and the results show
that they can be used as effective, thin, flexible and ultra lightweight shielding materials. The
15
shielding studies shows that the increase in the PEDO
T/PSS concentration in the buckypaper
improves the absorption contribution to the total shielding effectiveness of the PEDOT/PSS
coated MWCNTs bucky paper. The maximum SE of 55 dB at a critical thickness of 0.4 mm was
obtained.
[0046]
Although embodiments for
the present subject matter have been described in language
5
specific to structural features, it is to be understood that the present subject matter is not
necessarily limited to the specific features described. Rather, the specific features and methods
are
disclosed as embodiments for the present subject matter. Numerous modifications and
adaptations of the system/component of the present invention will be apparent to those skilled in
the art, and thus it is intended by the appended claims to cover all such
modifications and
10
adaptations which fall within the scope of the present subject matter.

Claims:We claim:
1. A process for preparation of conducting polymer wrapped multiwalled carbon nanotubes (MWCNT) for the fabrication of conducting polymer wrapped multiwalled carbon nanotube buckypaper (105), the process comprises:
(a) Unbundling of multiwalled carbon nanotubes in the acetone solvent using homogenizer;
(b) Adding conducting polymber poly (3, 4-ethylene dioxythiophene)/polystyrene sulfonate aqueous dispersion (PEDOT:PSS) to the unbundled multiwalled carbon nanotube;
(c) Homogenizing the mixture of the PEDOT:PSS and the unbundled multiwalled carbon nanotube to coat the conducting polymer; and
(d) Filtering the PEDOT:PSS and the unbndled MWCNT suspension to obtain the polymer wrapped MWCNT buckypaper.

2. The process as claimed in claim 1, wherein the polymer is selected for coating on multiwalled carbon nanotube is PEDOT:PSS poly (3, 4-ethylene dioxythiophene)/polystyrene sulfonate and the like polyaniline, polythiophene, polypyrrole.

3. The process as claimed in claim 1, wherein ratio of the conducting polymer in 0.013, 0.026 and 0.065 g of 1.3 wt% of PEDOT/PSS aqueous dispersion, is thoroughly mixed with the multiwalled carbon nanotubes (MWCNTs).

4. The process as claimed in claim 1, wherein the conducting polymer coated multiwalled carbon nanotube suspension (103) is filtered using vacuum infiltration technique.

5. The process as claimed in claim 1, wherein the PEDOT/PSS coated MWCNT bucky paper (105) is allowed to dry in vacuum oven at 60o C.

6. The process as claimed in claim 1, wherein the conducting polymer coated multiwalled carbon nanotube buckypaper (105) has shielding effectiveness of 55 dB, 52 dB, and 31 dB.

7. The process as claimed in claim 1, wherein the conducting polymer coated multiwalled carbon nanotube buckypaper (105) is effective for EMI shielding and antistatic applications.

8. The process as claimed in claim 1, wherein the PEDOT/PSS adds polarons and bipolarons in the MWCNT buckypaper to increase SEA.

9. The process as claimed in claim 1, wherein the homogenized time for the mixture of the poly (3, 4-ethylene dioxythiophene)/polystyrene sulfonate and the unbundled multiwalled carbon nanotube is in range of ½ hour to 2 hours.

10. The process as claimed in claim 1, wherein the conducting polymer is mixed in different ratios with the multiwalled carbon nanotube and homogenizing both in the acetone solvent.
, Description:A PROCESS FOR THE FABRICATION OF CONDUCTING POLYMER ENCAPSULATED MULTIWALLED CARBON NANOTUBE BUCKYPAPERS FOR PROTECTIVE APPLICATIONS

FIELD OF INVENTION
[001] The present invention is related to the preparation of conducting polymer encapsulated in Multiwalled Carbon Nanotube (MWCNT) buckypaper and its applications. More particularly the present invention discloses thin sheets of MWCNT/conducting polymer which can find applications in shielding of electromagnetic interference in Ku-band and for dissipating electrostatic charge.

BACKGROUND OF INVENTION
[002] In current scenario, Electrically conducting polymer-matrix composites have gained popularity for electromagnetic interference shielding applications because they are lightweight, resistant to corrosion, and flexible and easily processed. These kinds of flexible conductive composites may be used for typical antenna systems, lightning-protected aircraft composite panels, avionics line replaceable unit (LRU) enclosures, connector gaskets, electrostatic and space charge dissipation materials, different types of electronic pressure sensitive switches or sensors, and many other uses. These polymeric composites must be made conductive by compounding them with an electrically conducting filler, such as metal particles and filaments, carbon particles (e.g., graphite and carbon black), and carbon fibers, in order to achieve the required shielding effectiveness. For any filler, the EMI shielding effectiveness increases with increasing filler concentration in the composites, but the maximum filler loading is limited by the poor composite mechanical properties at high filler loadings resulting from the poor filler-matrix bonding. For materials and process cost saving and good mechanical properties, the attainment of a high shielding effectiveness at a low filler loading is desirable.
[003] With the development of powerful electronic and electrical equipments, EMI shielding becomes a significant factor for proper functioning of equipments and in the prevention of human health hazards. The materials generally used for shielding includes metals and metallic composites. But they are associated with several disadvantages like heavy weight, corrosion, and expensive processing techniques. Conducting polymer coated multiwalled carbon nanotube presents an alternative for EMI shielding because of lightweight, anti-corrosion, excellent conductivity and environmental stability.
[004] Conducting polymer coated multiwalled carbon nanotube buckypaper being lightweight; having high electrical conductivity can be easily encapsulated within structures. These exciting features of conducting polymer coated multiwalled carbon nanotube buckypaper make it a strong alternate to replace metal based EMI shielding and antistatic structures.
[005] Following are the works done so far in the field of conductive polymers based materials for protective EMI shielding:
[006] US 20100188833A1 (Electromagnetic interference shielding structure including carbon nanotube or nanofiber films and methods). The patent relates to designing of a composite material for electromagnetic interference shielding. The composite material comprises a stack including at least two electrically conductive nanoscale fiber films, which are spaced apart from one another by at least one insulating gap positioned between the at least two nanoscale fiber films. The stack is effective to provide a substantial multiple internal reflection effect. An electromagnetic interference shielded apparatus and a method for shielding an electrical circuit from electromagnetic interference is provided.
[007] US 6870092B2 (Methods and apparatus for EMI shielding) In this patent details have been given with respect to methods and apparatus for improving the resiliency and airflow through a honeycomb air vent filter while providing EMI shielding. In one embodiment, the honeycomb can be manufactured from a dielectric (e.g., plastic) substrate to provide improved resistance to deformation as compared to conventional aluminum honeycomb. The dielectric honeycomb substrate is metallized to provide EMI shielding capability. The metallized honeycomb substrate is cut slightly oversize to fit an opening in an electronic enclosure, which results in elastic deformation of resilient perimeter spring fingers that are used to hold the metallized dielectric honeycomb in place and provide electrical conductivity between the metallized dielectric substrate and the enclosure, thereby eliminating the use of a frame. In another embodiment, additional conductive layers can be added to the metallized dielectric honeycomb. In yet another embodiment, the metallized dielectric honeycomb substrate can be utilized in a framed configuration to provide improved durability.
[008] CN103266542A (Preparation method of carbon nanotube electromagnetic wave shielding paper) The invention relates to a method for preparing carbon nanotube electromagnetic wave shielding paper, which comprises the following steps: (a) adding a carbon nanotube into solvent, then adding resin and surfactant, performing dispersion treatment, and uniformly stirring, thus preparing carbon nanotube ink; and (b) by taking the carbon nanotube ink as a raw material, designing a printed mesh line pattern according to the requirements for shielding performance, printing carbon nanotube electromagnetic wave shielding paper in an ink jet printing mode, drying, and finishing, wherein the carbon nanotube ink contains 10-95wt% of solvent, 0.1-20wt% of carbon nanotube, 2-50wt% of resin and 0.1-5wt% of surfactant; the line width W1 of the mesh line pattern is 1-500mu m, the width W2 of the blank part is 1-500mu m, and the area ratio of the mesh lines is 20-99.9%. The method provided by the invention can be used for preparing electromagnetic wave shielding paper, and has the advantages of simple process and raw material saving; and the shielding paper is wide in shielding wave band, adjustable in property, portable and easy to use, and can be widely used hopefully.
[009] US20100000770A1 (Conducting Nanotubes or Nanostructures Based Composites, Method of Making Them and Applications). The patent relates to the preparation of an electromagnetic interference (EMI) shielding material which includes a matrix of a dielectric or partially conducting polymer, such as foamed polystyrene, with carbon nanotubes or other nanostructures dispersed therein in sufficient concentration to make the material electrically conducting. The composite is formed by dispersing the nanotube material in a solvent in which the dielectric or partially conducting polymer is soluble and mixing the resulting suspension with the dielectric or partially conducting polymer. A foaming agent can be added to produce a lightweight foamed material. An organometallic compound can be added to enhance the conductivity further by decomposition into a metal phase.

[0010] CN104093787A (Resin composition for emi shielding, comprising carbon hydride composite) The patent gives details of resin composition for electromagnetic interference shielding. More particularly, provided is a resin composition having superior dispersibility and impact relaxation and high conductivity, the resin comprising: (a) 100 parts by weight of a resin; based on 100 parts by weight of the resin, (b) 0.1 to 15 parts by weight of a carbon nanotube surface-modified in a condition of the absence of oxidant; and (c) 1 to 40 parts by weight of a carbon compound, a metal, a metal compound, or a mixture thereof. The resin composition for electromagnetic interference shielding, comprising a carbon hydride composite, is specifically useful in an electronic control unit material for weight reduction of car, and thus can be replaced with a high-priced heavy metal material.

[0011] US20080057265A1 (Electromagnetic Interference Shielding Structure Including Carbon Nanotubes and Nanofibers) The invention relates to designing electromagnetic interference (EMI) shielding structure and methods of making such structures are provided. In one case, a method is provided for making a lightweight composite structure for electromagnetic interference shielding, including the steps of providing a nanoscale fiber film which comprises a plurality of nanoscale fibers; and combining the nanoscale fiber film with one or more structural materials to form a composite material which is effective as an electromagnetic interference shielding structure. In another case, a method is provided for shielding a device which includes an electrical circuit from electromagnetic interference comprising the steps of providing a nanoscale fiber film which comprises a plurality of nanoscale fibers; and incorporating the nanoscale fiber film into an exterior portion of the device to shield an interior portion of the device from electromagnetic interference.
[0012] US20060241236A1 (Electromagnetic radiation attenuation) The patent describes an electromagnetic radiation attenuating material or coating consistent with certain embodiments of the present invention uses a binding matrix with an operative quantity of electromagnetic radiation attenuating nano-particles suspended in the binding matrix, wherein, the electromagnetic radiation attenuating nano-particles comprise onion-like-carbon (OLC) particles. In other embodiments, freestanding structures, aerosols and powders or suspensions contained within an enclosure provide EM or Radar absorption, particularly in the range of about 500 MHz to about 30 THz. This abstract is not to be considered limiting, since other embodiments may deviate from the features described in this abstract.
[0013] US7008563B2 (Polymer-wrapped single wall carbon nanotubes) The present invention relates to new compositions of matter and articles of manufacture comprising SWNTs as nanometer scale conducting rods dispersed in an electrically-insulating matrix. These compositions of matter have novel and useful electrical, mechanical, and chemical properties including applications in antennas, electromagnetic and electro-optic devices, and high-toughness materials. Other compositions of matter and articles of manufacture are disclosed, including polymer-coated and polymer wrapped single-wall nanotubes (SWNTs), small ropes of polymer-coated and polymer-wrapped SWNTs and materials comprising same. This composition provides one embodiment of the SWNT conducting-rod composite mentioned above, and also enables creation of high-concentration suspensions of SWNTs and compatibilization of SWNTs with polymeric matrices in composite materials. This solubilization and compatibilization, in turn, enables chemical manipulation of SWNT and production of composite fibers, films, and solids comprising SWNTs.
[0014] WO1990009027A1 (Use of electrically conducting polymer composites) The subject invention is direct towards novel use of a polymer composite as thermoplastic raw material for products with electrically conducting or semiconducting properties. In polymer composites known in the field electrically conducting fillers and polymers do not have thermoplastic properties and are accordingly ill suited for thermoplastic processing of conducting and semiconducting products. It has now been invented that a polymer composite made up of an electrically nonconducting polymer matrix or polymer substrate, doped or undoped poly(3-substituted thiophene) and possibly plastics additives, is well suited as raw material for thermoplastics with conducting or semiconducting properties. The invention is accordingly also directed towards antistatic and semiconducting applications, where good shielding against electromagnetic interference is required and applications where the discovered piezoelectric properties of this material can be used.
[0015] It would therefore be desirable to provide improvements in EMI shielding structures having multiwalled carbon nanotubes and/or nanofiber films. In particular, it would be desirable to provide improved EMI shielding structures that may be produced in a relatively lightweight form and at a relatively low cost. It also would be desirable to provide a method for producing multiwalled carbon nanotubes for EMI shielding applications.
OBJECTIVE OF THE INVENTION:
[0016] The main objective of the present invention is to fabricate efficient conducting polymer encapsulated multiwalled carbon nanotube buckypaper for EMI shielding and antistatic applications.
[0017] Another object of the invention is to develop light weight, corrosion resistant, and easily process able materials with excellent shielding behavior towards electromagnetic waves and possessing anti-static properties.

SUMMARY OF THE INVENTION:
[0018] The present invention relates to a process/method of fabricating conducting polymer encapsulated multiwalled carbon nanotubes (MWCNT) buckypaper and its applications. The method comprising:
(a) Unbundling of multiwalled carbon nanotubes in organic solvent by homogenizer. Addition of conducting polymer to the unbundled multiwalled carbon nanotube suspension and again homogenizing the mixer for two hours.
(b) The conducting polymer is mixed in different ratios of multiwalled carbon nanotube and then making buckypaper by vacuum infiltration technique.
(c) Measuring the shielding effectiveness and anti-static properties of the buckypapers by vector network analyzer and static decay meter, respectively.
[0019] In one embodiment of the present invention, the conducting polymer is selected for study is aqueous dispersion of poly (3, 4-ethylene dioxythiophene)/polystyrene sulfonate.
[0020] In another embodiment of the present invention, the multiwalled carbon nanotube is used for making buckypaper.
[0021] In another embodiment of the invention, the medium used for unbundling of multiwalled carbon nanotube is selected from acetone and the like.
[0022] In another embodiment of the invention, the mixing of conducting polymer with the multiwalled carbon nanotube dispersion is kept to 2 hours.
[0023] In another embodiment of the invention, the conducting polymer coated multiwalled carbon nanotube dispersion obtained was filtered over filter paper and dried in vacuum oven at 60 0C.
[0024] In another embodiment of the invention, the conducting polymer encapsulated multiwalled carbon nanotube bucky papers were tested for EMI shielding and anti-static applications.
[0025] In order to further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit scope of the present subject matter.

BRIEF DESCRIPTIONS OF THE DRAWINGS
[0026] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[001] Fig. 1 illustrates preparation of PEDOT/PSS coated MWCNT bucky paper, in accordance with an embodiment of the present subject matter;
[002] Fig. 2 illustrates (a) Digital image of PEDOT/PSS coated buckypaper, (b) low magnification SEM of PEDOT/CNT2 buckypaper (c) high magnification SEM of PEDOT/CNT2 buckypaper (d) EDAX analysis, in accordance with an embodiment of the present subject matter;
[003] Fig. 3 illustrates XRD patterns of PEDOT/PSS coated MWCNT buckypapers, in accordance with an embodiment of the present subject matter;
[004] Fig. 4 illustrates thermogravimetric analysis of the samples, in accordance with an embodiment of the present subject matter;
[005] Fig. 5 illustrates Raman spectrum of PEDOT/PSS coated MWCNT buckypapers, in accordance with an embodiment of the present subject matter;
[006] Fig. 6 illustrates variation of total shielding effectiveness with frequency, in accordance with an embodiment of the present subject matter;
[007] Fig. 7 illustrates shielding effectiveness due to absorption loss, in accordance with an embodiment of the present subject matter;
[008] Fig. 8 illustrates shielding effectiveness due to reflection loss, in accordance with an embodiment of the present subject matter; and
[009] Fig. 9 illustrates static charge decay time plots of PEDOT /PSS coated buckypaper, in accordance with an embodiment of the present subject matter.
[0010] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0027] At the very outset of the detailed description, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only exemplary embodiment, and without intending to imply any limitation on the scope of this invention. Accordingly, the description is to be understood as an exemplary embodiment and teaching of invention and not intended to be taken restrictively.
[0028] The present subject matter relates to a process for preparation of cinducting polymer coated multiwalled carbon (MWCNT) buckypaper for EMI shielding and antistatic applications. In the present process, an aqueous dispersion of PEDOT:PSS, i.e., poly(3,4-ethylenedioxythiophene) polystyrene sulfonate which is polymer is mixed with unbundled suspension of multiwalled carbon nanotubes (MWCNT). Further, the mixer is homogenized thoroughly so that the polymer molecules get adsorbed on the multiwalled carbon nanotubes. After homogenizing for half an hour to two hour, the conducting polymer is coated on the multiwalled carbon nanotube. After homogenizing, the suspension of the MWCNT and polymer is filtered by vacuum infiltration technique, i.e., filter paper Whatman no. 44 is used for the filtration. The PEDOT contains aromatic thiophene rings in the polymeric chain allows strong p-p stacking with the hybridized carbon on the surface of the MWCNTs. Moreover, PSS is a surfactant which helps MWCNTs to disperse, and its long chain surround the surface of MWCNTs to inhibit stacking. Finally after filtration, the PEDOT/PSS coated MWCNT buckypaper is allowed to dry in vacuum oven at 60 oC. Finally, the conducting polymer wrapped multiwalled carbon nanotubes is obtained with increased EMI SE value.
[0029] The present invention relates to a process for the preparation of thin papers of conducting polymer encapsulated MWCNT buckypaper which can find applications in shielding of electronic and electrical equipments besides as antistatic material. The process involves preparation of thin, flexible sheet of carbon nanotubes (CNTs) alongwith different loadings of conducting polymer poly ethylenedioxthiophene (PEDOT) prepared by vacuum infiltration technique, termed as buckypaper which can be used for specific applications.
[0030] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0031] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0032] Figure 1 describes the process of fabrication of PEDOT encapsulated MWCNT paper for the EMI shielding and antistatic applications. Initially, multiwalled carbon nanotube (MWCNTs) 101 are unbundled in acetone medium by homogenizer, then polymer PEDOT: PSS (i.e., poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) 102 is added to the MWCNT dispersion and again homogenized for ½ hours to 2 hrs. The PEDOT:PSS encapsulated MWCNTs dispersion is then filtered by vacuum infiltration technique using Whatman filter paper 44 104. Finally, the PEDOT:PSS encapsulated or polymer encapsulated MWCNT buckypaper 105 is peeled off from the filter paper after 2 hrs of drying in vacuum oven at temperature of 60o C. Some examples of preparation are given below.

Example 1
[0033] Preparation of conducting polymer coated multiwalled carbon nanotube buckypaper
An aqueous dispersion of PEDOTPSS (1.3 wt %) was mixed with unbundled suspension of multiwalled carbon nanotubes and mixer was homogenized thoroughly so that polymer molecule get adsorbed on the multiwalled carbon nanotubes. After homogenizing for half an hour, the conducting polymer coated multiwalled carbon nanotube suspension was filtered by vacuum infiltration technique, filter paper Whatman no. 44 is used for the filtration. The PEDOT contains aromatic thiophene rings in the polymeric chain, which allows strong p-p stacking with the hybridized carbon on the surface of the MWCNTs. Moreover, PSS is a surfactant which helps MWCNTs to disperse, and its long chain surround the surface of MWCNTs to inhibit stacking. Finally after filtration, the PEDOT/PSS coated MWCNT bucky paper is allowed to dry in vacuum oven at 60 oC.

Example 2
[0034] Preparation of PEDOT/MWCNT buckypaper with 5 % of PEDOT
First of all MWCNTs were dispersed in an organic solvent using homogenizer for 15 minute. After that, 5 ml of PEDOT/PSS was added to the dispersion of the MWCNTs, and again homogenized for half an hour. So that PEDOT/PSS is coated over the MWCNTs. The suspension of PEDOT/PSS and MWCNTs is then filtered using vacuum infiltration technique, filter paper Whatman no. 44 was used for the filtration. Finally after filtration, the PEDOT/PSS coated MWCNT bucky paper was allowed to dry in vacuum oven at 60 oC.

Example 3
[0035] Preparation of PEDOT/MWCNT buckypaper with 10 % of PEDOT
Initially MWCNTs, 0.25 g were unbundled using homogenizer and then 10 ml of 1.3 wt% of aqueous dispersion of the PEDOT:PSS was added to the suspension of unbundled MWCNTs. The mixer of MWCNTs and PEDOT:PSS was again homogenized for half an hour, for the adsorption of PEDOT:PSS over the surface of MWCNTs. Finally, the mixer was filtered using vacuum filtration unit, Whatman no. 44 filter paper was used for the filterationand dried in a vacuum oven at 60 °C. After drying a thin films of PEDOT:PSS coated MWCNTs buckypaper was peeled off from the filter paper.

[0036] Figure 2 (a) shows the digital image of the PEDOT/PSS coated MWCNTs bucky paper, from the naked eyes all bucky paper looks like smooth, uniform, black thin sheets. The figure 2 (b) shows the low magnification SEM image of the bucky paper which reveals slightly uneven rough surface of the paper. Figure 2 (c) shows the high magnification image of the bucky paper, where individual MWCNTs are clearly visible. The MWCNTs forms a random, extremely, interconnected macroporous structure. It is also observed that most of the MWCNTs are unbundled while bundles of MWCNTs can also be seen. The inset shows morphology of the individual PEDOT/PSS coated MWCNT analyzed by using TEM which clearly shows the nano-tubular structure of the crystalline MWCNTs and the PEDOT/PSS thin layer coated as a sheath at the surface of MWCNTs. Figure 2 (d) is the EDAX pattern; presence of 18% of sulfur atoms confirms the presence of thiophene and polystyrene sulfonate moieties in the MWCNTs buckypaper.
[0037] Figure 3 shows XRD patterns of the samples in which characteristic peaks of MWCNTs observed at 2? value 26.2o and 42.5o for the corresponding planes (002) and (100) respectively, attributed to the hexagonal graphitic structure. The peak of PEDOT:PSS is not appeared in the PEDOT/CNT1 and PEDOT/CNT2 buckypapers because of the very low concentrations of PEDOT/PSS whereas in PEDOT/CNT3 shows a broad peak at 12o due to the amorphous nature of PEDOT/PSS.
[0038] Figure 4 shows TGA curves of the buckypapers which showed three major weight losses due to the degradation of PEDOT/PSS. The first step is at about 100 oC which indicates the loss of adsorbed water molecules. The second loss takes place at about 180 oC due to the loss of dopant molecules from the polymer chain. Finally, the third major loss is near about at 310 oC, attributed to the degradation of polymeric backbone. From the thermogram it is clearly seen that the addition of PEDOT/PSS gradually decreases the stability of the PEDOT/PSS coated MWCNT buckypapers.
[0039] Figure 5 shows Raman spectrums of PEDOT/CNT1 and PEDOT/CNT2 which shows no peaks of PEDOT/PSS but peaks associated with MWCNTs are clearly visible. They show peaks at ~1310 (D-band) and 1580 cm?1 (G-band) due to the disorder in the carbon system and in-plane vibration of the C ? C bond because of graphite, respectively. The band around 2700 cm?1 was also appears in these samples which is overtone of D-band known as G' band. In the PEDOT/CNT3 sample, bands related to PEDOT structure are strong visible in the spectrum.

[0040] Figure 6 shows total shielding effectiveness of the buckypapers which increases with increases in the concentration of PEDOT/PSS. The maximum SE of 55 (dB) was obtained with PEDOT/CNT3 at 12.4 GHz frequency, whereas PEDOT/CNT2 and PEDOT/CNT1 shows 52 and 31 dB of SE, respectively. For commercial applications only 20 dB of SE is required, which suggests these samples can be effectively used for EMI shielding applications.

[0041] Figure 7 and 8 shows the shielding mechanisms i.e. SEA (SE due to absorption loss) and SER (SE due to reflection loss) which are responsible for EMI shielding. It is clearly observed from the figure 6 that the contributions to the SE values mainly come from the absorption rather than reflection mechanism. It is interesting to note that the on increasing the concentration of PEDOT/PSS in the buckypaper the SEA increases linearly. On increasing PEDOT/PSS loading from 5.2-26 wt% in the buckypaper the SEA increases from 62% to 77%, respectively. This is due to the fact that addition of PEDOT/PSS adds more polarons and bipolarons in the buckypaper which enhances the SEA significantly.

Example 4
[0042] EMI shielding of conducting polymer coated multiwalled carbon nanotube buckypaper
EMI shielding measurements were carried out using an Agilent E8362B Vector Network Analyzer with a coaxial cable attached with a rectangular waveguide of the Ku-band (15.75 mm × 7.85 mm). The samples were cut into rectangular films of standard Ku-band dimensions. From figure 6 it is observed that the total shielding effectiveness of the buckypapers increases with increases in the concentration of PEDOT/PSS. The maximum shielding effectiveness of 55 (dB) was obtained with PEDOT/CNT3 at 12.4 GHz frequency, whereas PEDOT/CNT2 and PEDOT/CNT1 shows 52 and 31 (dB) of shielding effectiveness, respectively. To understand the shielding mechanism, the total shielding effectiveness is further resolved into SEA and SER components as shown in figure 7 and 8, respectively. It is clearly observed from the figure that the contributions to the shielding effectiveness values mainly come from the absorption rather than reflection mechanism. On increasing the concentration of PEDOT/PSS in the buckypaper the SEA increases linearly.
Example 5
[0043] Antistatic measurements of conducting polymer coated multiwalled carbon nanotube buckypaper
The antistatic measurements of conducting polymer coated multiwalled carbon nanotube buckypapers were carried out by JCI 166v5 charge decay test unit. For antistatic properties there are two set criteria to dissipate static charge from its surface; 1) criterion 1/e – measure decay time of initial peak voltage to reach 1/e (37%) and 2) criterion 10% ? measure decay time of initial peak voltage to reach 10%. For a material to be antistatic the decay time should be less than half a second in the 1/e criterion and for 10% criterion the decay time should be less than two seconds. Figure 9 shows the static charge decay times of the PEDOT/CNT1, PEDOT/CNT2, and PEDOT/CNT3 buckypapers measured by applying a positive potential of 5k V. From the figure it is observed that all three samples easily surpass the set criteria of 1/e within 0.3 second and 10% within 0.8 seconds which is due to the highly conducting nature of the PEDOT/PSS and MWCNTs. Figure 9, show 1/e static charge decay time of PEDOT/CNT1 buckypaper is 0.14 second whereas PEDOT/CNT2 and PEDOT/CNT3 shows decay time of 0.15 and 0.24 second, respectively, is observed for PEDOTCNT3. Any material showing static decay time less than 2 seconds is suitable for antistatic applications.
[0044] Table I: EMI shielding data of various combinations of PEDOT incorporated in MWCNT matrix. Test result.

Table 1
SI No. Sample PEDOT/PSS MWCNTs SET SEA SER
1. PEDOT/CNT1 0.013 g 0.25 31.73 19.94 11.79
2. PEDOT/CNT2 0.026 g 0.25 52.17 35.79 16.38
3. PEDOT/CNT3 0.065 g 0.25 55.11 42.66 12.45
[0045] Microwave absorption behaviour of PEDOT/PSS coated MWCNTs bucky papers were investigated in the microwave frequency range of 12.4-18 GHz (Ku-band) and the results show that they can be used as effective, thin, flexible and ultra lightweight shielding materials. The shielding studies shows that the increase in the PEDOT/PSS concentration in the buckypaper improves the absorption contribution to the total shielding effectiveness of the PEDOT/PSS coated MWCNTs bucky paper. The maximum SE of 55 dB at a critical thickness of 0.4 mm was obtained.
[0046] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.