Electrically conductive compositions of carbon particles and methods for their production

Electrically conductive compositions of carbon nparticles having thin coatings of conductive polymer are disclosed. The thin coatings of conductive polymer electrically interact with each carbon particle and protect the carbon particles from conductive failure. Because the conductive compositions of coated carbon particles maintain their conductive characteristics even after long term exposure to chemicals, they are useful as filler materials in polymer compositions utilized to fabricate chemical delivery devices.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to conductive carbon particles having 
improved performance as a filler material and improved dispersability 
within a matrix material. More particularly, the present invention 
involves compositions of carbon particles having coatings of conductive 
polymer which electrically and physically interact with the carbon 
particle to protect the carbon particle from conductive failure and 
provide an effective interface between the carbon particle and a matrix 
material, such as a polymer. 
2. Description of Related Art 
Carbon has found extensive utility recently in a variety of applications 
where its electrical conductivity, low density, low cost, and ease of 
processing are especially attractive. In particular, carbon in the form of 
particulates such as carbon black is widely used as a conductive filler 
material for polymers utilized to fabricate housings for electronic 
equipment, floor mats for electronic assembly areas, volatile chemical and 
fuel transport lines, conductive adhesives, electronic components and 
storage bins. The usefulness of carbon black in these applications is 
primarily attributed to its low density and its ability to dissipate 
accumulated static charges as well as prevent the build-up of static 
charges. 
The static dissipation property of carbon prevents possible catastrophic 
explosions and/or fires which can result when charges accumulate and 
discharge in the form of sparks during the movement of fuels or volatile 
chemicals through polymeric transport lines. In the case of its utility in 
electronic housings, the static dissipation property prevents potentially 
damaging loss of data or equipment malfunction caused by discharging 
sparks from static charges which have built-up on the housing. 
Additionally, carbon filled composites can be pressed and molded to form 
and retain almost any shape. 
Additionally carbon particulates or monolithic devices fabricated from 
carbon are useful in fabricating batteries and electrodes. Again, the low 
density and electrical conductivity of carbon makes this material 
attractive in applications where light weight conductive materials are 
preferred. 
One problem associated with relying upon the conductive properties of 
carbon over an extended period of time relates to its highly adsorbent 
surface. In addition to being useful for its conductive properties, carbon 
is suitable for purifying and removing unwanted and especially highly 
colored components in liquid mixtures. Because the surface of carbon 
particles is a particularly good adsorbent for organic compounds, it is 
routinely utilized to remove soluble and insoluble organic impurities in 
aqueous systems. Unfortunately, this superior ability to adsorb compounds 
within its environment frequently results in a loss or significant 
reduction in the conductivity of carbon exposed to certain environments. 
For example, chemical and fuel transport lines fabricated of polymers 
filled with carbon particles can become non-conductive as a result of the 
adsorption and interaction of the carbon particles with the chemical or 
fuel. Similarly, conductive carbon particle filled polymeric devices 
utilized in reactive gas or other hostile environments can lose their 
conductivity once exposed to the reactive gas or hostile environment for a 
sufficient length of time. 
Conductive organic polymers have also found utility in the fabrication of 
devices having static-dissipation properties and in the fabrication of 
electrodes. Since these polymers are considerably more costly than carbon, 
are not structural materials and do not have the physical characteristics 
to be effective filler material, conductive polymers are limited in their 
practical static-dissipation usefulness. 
In the case of their usefulness in electrochemical cells, however, 
conductive organic polymers have gained widespread attention. For example, 
conductive forms of polyaniline are widely recognized for their utility in 
electrochemical cells as a cathode or an anode. Additionally, in some 
electrochemical applications, conductive polymers are combined with 
carbon, to provide carbon filled polymeric composites for fabricating 
electrodes. The conductive polymer is the portion of the electrode which 
charges and discharges and is the primary functioning component of these 
conductive polymer/carbon electrodes. For this reason, the combination of 
carbon and polymer contains large amounts of polymer and relatively small 
amounts of carbon, the carbon being present primarily as a conductive 
filler material which provides strength and a substance to the mixture 
while maintaining the conductive nature of the polymer. Secondarily, the 
carbon may serve as a pathway of current flow as the conductive polymer is 
oxidized/reduced. 
Typically, battery components of carbon and conductive polymer composites 
are prepared by merely mixing the conductive polymer and carbon using 
relatively large amounts of polymer and smaller amounts of carbon and then 
pelletizing the mixture into a homogeneous monolithic composite of carbon 
in a polymeric matrix. For example, U.S. Pat. No. 4,803,138 discloses 
polyaniline electrodes of pressed polyaniline powder, 
polytetrafluoroethylene and about 10 wt % carbon black. The amount of 
electrical interaction between carbon filler and conductive polymer in 
these composites is limited by the degree of physical intimacy between the 
filler and polymer obtained during the pressing operation. 
Another similar application involves preparing uniform dispersions of 
carbon in pressed carbon electrodes. This application, disclosed in 
Japanese Patent Bulletin (A) 1987-64828, involves synthesizing 
non-conductive polyaniline in the presence of carbon to provide more 
uniform carbon compositions and improved mechanical strength for carbon 
electrodes prepared from the compositions. 
Accordingly, it is an object of the present invention to provide 
electrically conductive compositions having improved resistance to loss of 
conductivity. 
It is further an object of the present invention to provide electrically 
conductive compositions of carbon particles which maintain their physical 
and electrical characteristics in the presence of chemically reactive and 
hostile environments. 
It is additionally an object of the present invention to provide 
electrically conductive compositions of carbon particles for use as filler 
material in formulations having anti-static properties. 
SUMMARY OF THE INVENTION 
The present invention accomplishes the above-described objectives by 
providing carbon particles having a thin coating of conductive polymer. 
The thin polymer coating provides a stable and chemically resistant 
protective barrier to environmentally induced changes in the surface of 
the carbon particles. In the absence of the thin coating of conductive 
polymer, these changes lead to the loss of carbon particle electrical 
conductivity, a characteristic that frequently forms the basis for 
incorporating carbon particles in, for example polymeric formulations, as 
filler material. 
Additionally, the present invention provides methods for preparing 
conductive polymer coated carbon particles which result in enhanced 
physical and chemical interactions between the conductive polymer coating 
and the carbon particles. The high degree of interaction between the 
carbon particle and the thin conductive coating provides an effective 
electrical bridge to the carbon particle without reducing the physical 
characteristics of carbon particles which make carbon an effective filler 
material. 
More particularly, the present invention provides electrically conductive 
compositions of a plurality of carbon particles each of which has a thin 
coating of conductive polymer in an amount sufficient to provide a coating 
weight of from approximately 5 wt % to approximately 50 wt % of the 
electrically conductive composition. While any of a number of conductive 
polymers is suitable for forming the coating, conductive polyaniline is 
preferred for its stability and its excellent conductivity. 
The electrically conductive compositions of the present invention have 
electrical conductivities which are primarily dependent upon the size, 
shape, morphology and density of the carbon particles, the method selected 
for preparing the conductive polymer and the method of coating carbon 
particles, and the particular selected conductive polymer. Typically, 
however, the conductive compositions of the present invention have bulk 
conductivities of at least 0.05 S/cm which is sufficiently high for 
electrically conductive fillers useful in antistatic and charge 
dissipation applications. 
An exemplary process for preparing the electrically conductive compositions 
of the present invention includes forming a slurry of carbon particles in 
a solution of the "free-base" polymer, or nonconductive form, in an 
organic solvent. Adding water to this slurry causes the polymer to 
precipitate onto the surface of the carbon particles. Then doping the 
polymer coating generates a conductive form of the polymer and provides 
carbon particles having a coating of conductive polymer. An alternative 
preferred method involves synthesizing the conductive polymer in a slurry 
of carbon particles so that the polymer is formed simultaneous with the 
coating process. More particularly, a predetermined amount of selected 
monomer is polymerized in a suitable solvent which also incorporates a 
slurry of deaggregated and prewetted carbon particles. As the monomer 
converts to polymer, the forming polymer deposits itself on the surface of 
the carbon particles forming a thin coating. After the polymerization 
process terminates, the coated particles are collected, washed and dried. 
The result is free-flowing electrically conductive coated carbon particles 
which retain their electrical conductivity even when exposed to hostile 
environmental conditions such as reactive gases and chemicals. 
The electrically conductive compositions of coated carbon particles of the 
present invention are particularly useful as particulate filler material 
in polymer formulations used to fabricate articles having antistatic and 
charge dissipation properties. For example, carbon particles having a thin 
coating of conductive polymer are suitable for incorporating into 
polymeric formulations from which chemical transport lines are extruded. 
The resulting electrically conductive chemical transport lines have long 
term conductive properties and are not subject to conductive failure from 
exposure. The thin coating of electrically conductive polymer protects the 
surface of the carbon particles from the detrimental effects of exposure 
to chemicals and fuels and is responsible for the long term high 
conductivity of the coated particle. 
Further objects, features and advantages of the conductive polymeric 
compositions of the present invention, as well as a better understanding 
thereof, will be afforded to those skilled in the art from a consideration 
of the following detailed explanation of preferred exemplary embodiments 
thereof.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
The present invention is based upon the discovery that the performance of 
carbon particles which are widely used as electrically conductive filler 
material for polymers can be enhanced with a thin coating of conductive 
polymer without losing their electrical or physical characteristics. 
Moreover, unlike uncoated carbon particles, the coated carbon particles of 
the present invention can be exposed to polymers, chemicals and fuels 
without adversely effecting their ability to conduct electricity. It is 
believed that the conductive polymer maintains the electrical integrity of 
the carbon while shielding the carbon surface from reacting and adsorbing 
chemicals and polymeric additives. In the absence of the polymeric 
coating, the surfaces of the carbon particles eventually become passivated 
and cause the conductive failure of the whole particle. 
The electrically conductive coated carbon particles which are the subject 
of the present invention are useful in virtually all applications in which 
carbon filler particles have utility. Those skilled in the art will 
appreciate that the most advantageous applications are those in which the 
electrical conductivity of carbon particles is the basis for its use. 
These applications vary widely and include filler materials for conductive 
polymeric adhesives used in the electronic industry, filler for battery 
electrodes, and filler in materials useful for preventing potentially 
dangerous static charge accumulation caused by friction between materials. 
The ability of carbon filler material to prevent static charge build-up or 
to dissipate static charge makes the conductive polymer coated carbon 
particles of the present invention useful filler material for polymers. 
Furthermore, the ability of the coated carbon particle compositions of the 
present invention to maintain electrical conductivity following long term 
exposure to chemicals and polymer additives makes them particularly 
suitable for extended use applications include coated carbon particle 
filled polymers used to fabricate textile fibers, transport lines for 
chemicals and fuels, housings for electronic equipment and floor mats for 
electronic assembly areas. 
Accordingly, the present invention provides electrically conductive 
compositions which include a plurality of carbon particles, each of which 
has a thin coating of conductive polymer in an amount sufficient to 
provide a coating weight of from approximately 5 wt % to approximately 50 
wt % of the composition. The carbon particles utilized in the compositions 
of the present invention are preferably in the form of discrete uniformly 
sized particles each of which has a thin coating of conductive polymer. 
That is, aggregates of carbon particulates are preferably minimized and 
the processes described herein for producing coated carbon particles 
provide relatively few numbers of coated aggregates of carbon 
particulates. However, it is expected that a certain number of coated 
carbon particles will exist in the form of coated aggregates of carbon 
particulates. Thus, for purposes of the present invention, coated 
aggregates of carbon particles in which more than one discrete carbon 
particulate forms an aggregate which itself has a thin coating of 
conductive polymer are within the definition of coated carbon particles. 
Additionally, unlike prior art combinations of carbon particles and 
conductive polymer which are in the form of polymeric composites, the 
compositions of the present invention are in the form of free flowing 
coated particles. That is, the compositions of the present invention are 
restricted in the amount of conductive polymer and include enough polymer 
to form a thin conductive coating on each carbon particle. In contrast, 
prior art solid composites are largely conductive polymer and include 
small amounts of carbon particles as filler material. The conductive 
polymer coatings present on the surface of the carbon particles are thin, 
which, as mentioned above, are approximately 5 wt % to approximately 50 wt 
% of the weight of the filler material. The thin conductive polymer 
coating formed by the methods described herein allows the coated carbon 
particles to retain the bulk electrical characteristics of uncoated carbon 
particles. As such, the coating of conductive polymer serves largely as a 
protective electrical interconnection between the carbon particle and its 
surrounding environment. Conductive polymer coatings of greater than about 
50 wt % of the filler material are useful as well and thicker coatings 
provide increased protective properties. However, the relative cost of the 
coated carbon particle increases with increases in conductive polymer 
coating thicknesses and there is a simultaneous decrease in electrical 
conductivity of carbon particles with thicker coatings. 
Suitable forms of carbon particles include carbon particles of varying 
graphitic content, size, morphology and shape. Such carbon particles are 
widely available from commercial sources such as Degussa Corporation and 
Cabot. Particle sizes can range from sub-micron particulates to fibers 
having diameters of up to 20 microns and aspect ratios as high as 1 to 
100. Additionally the surface area of carbon particles having utility in 
the present invention is typically at least 200 m.sup.2 /gram and as high 
as 2000 m.sup.2 /gram. Those skilled in the art will appreciate that 
carbon particles and carbon black in particular have physical and 
electrical conductivity properties which are primarily determined by the 
structure, particle size, morphology and surface chemistry of the 
particle. 
More particularly, carbon black particle structures can range from highly 
structured tree-like shapes to minimally structured rod-like shapes. 
Typically, the conductivity of carbon particles increases with increases 
in the structure of the particle from low structure to fine structure. 
Associated with the increase in structure is an increase in surface area 
which also increases conductivity. Similarly, the conductivity of highly 
crystalline or highly graphitic particles is higher than the conductivity 
of the more amorphous particles. Generally speaking, any of the 
above-described forms of carbon particles is suitable in the practice of 
the present invention and the particular choice of size, structure, and 
graphitic content depends upon the physical and conductivity requirements 
of the coated carbon particle. 
It is contemplated as being within the scope of the present invention to 
provide compositions of a plurality of carbon particles having a coating 
of any of a large variety of conductive polymers. Polymers having the 
capability of conducting electricity are documented in the literature, 
having been studied extensively during the past decade. A useful review 
article which discusses the synthesis and physical, electrical, and 
chemical characteristics of a number of conductive polymers is Conductive 
Polymers, Kanatzidis, M. G., C & E News, 36-54, Dec. 3, 1990. Some of the 
more useful classes of conductive polymers include unsaturated or aromatic 
hydrocarbons as well as nitrogen, sulfur, or oxygen containing compounds. 
The polymers include but are not limited to conductive forms of 
polyacetylene, polyphenylene, polyphenylenevinylene, polypyrrole, 
polyisothianaphthene, polyphenylene sulfide, polythiophene, 
poly(3-alkylthiophene), polyazulene, polyfuran, and polyaniline. For 
purposes of the present invention, conductive forms of polyaniline are 
preferred for forming the coating of conductive polymer. These conductive 
forms include self-doped, sulfonated polyaniline which is conductive 
without external doping. 
Polyaniline can occur in several general forms including a reduced form 
having the general formula 
##STR1## 
a partially oxidized form having the general formula 
##STR2## 
and the fully oxidized form having the general formula 
##STR3## 
Each of the above illustrated polyaniline oxidation states can exist in 
its base form or in its protonated form. Typically, protonated polyaniline 
is formed by treating the base form with protonic acids, such as mineral 
and/or organic acids. The electrical properties of polyaniline vary with 
the oxidation states and the degree of protonation, with the base forms 
being generally electrically insulating and the protonated form of 
polyaniline being conductive. Accordingly, by treating a partially 
oxidized base form of polyaniline, a salt having an increased electrical 
conductivity of approximately 1-10 S/cm is formed. 
The preparation and properties of polyaniline, both its non-conductive or 
"free base" form and its conductive "acid" form, are well documented in 
the literature. For example, U.S. Pat. Nos. 5,008,041, 4,940,517, 
4,806,271, disclose methods for preparing polyaniline under a variety of 
conditions for obtaining different molecular weights and conductivities. 
Typically, polyaniline is prepared by polymerizing aniline in the presence 
of a protonic acid and an oxidizing agent resulting in the "acid" 
protonated conductive form of the polymer. 
Protonic acids having utility in the synthesis of polyaniline include acids 
selected from the group consisting of HX, H.sub.2 SO.sub.4, H.sub.3 
PO.sub.4, R(COOH).sub.n, R'(COOH).sub.n, R(SO.sub.3 H).sub.n, R(PO.sub.3 
H).sub.n, R'(SO.sub.3 H).sub.n, R'(PO.sub.3 H).sub.n, wherein X is a 
halogen, R is hydrogen or substituted or unsubstituted alkyl moiety, R' is 
a substituted or unsubstituted aromatic moiety, and n is an 
integer.gtoreq.1. Exemplary acids include methane sulfonic acid, benzene 
sulfonic acid, toluene sulfonic acid, or acids having the formula HO.sub.3 
SR'--O--R"SO.sub.3 H wherein R' and R" are independently substituted or 
unsubstituted aromatic moieties. Substitutions for the aromatic moieties 
include halogen, alkyl, or alkoxy functionalities. 
As described in more detail below, in the practice of the present invention 
it may be preferable to prepare polyaniline with a protonic acid having 
the formula 
##STR4## 
wherein G and G' are independently hydrogen, lower alkyl, octyl, nonyl, or 
saturated or unsaturated linear or branched decyl, dodecyl, tetradecyl, 
hexadecyl, or octadecyl groups. Protonic acids belonging to this general 
class of compounds have surfactant properties which aid in dispersing and 
deaggregating carbon particles. Exemplary protonic acids having surfactant 
properties are selected from the group consisting of decyl diphenylether 
disulfonic acid and decylphenylether disulfonic acid. 
Generally, the counter-ion of the protonated conductive polyaniline is 
supplied by the protonic acid utilized in the polymerization. Accordingly, 
the counter-ion can be selected from a large number of ions including the 
anions of the aforementioned protonic acids. The nonconductive form of 
polyaniline can be prepared by deprotonating the doped conductive form, 
for example, by dissolving or slurrying the polymer in ammonium hydroxide 
solution, to form non-conductive polyaniline free base. 
It is further contemplated as being within the scope of the present 
invention to utilize sulfonated polyaniline compositions having the 
following general formula: 
##STR5## 
wherein 0.ltoreq.y.ltoreq.1; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, 
R.sub.6 are selected from the group consisting of H, --SO.sub.3, 
--SO.sub.3 H, --R.sub.7 SO.sub.3, --R.sub.7 SO.sub.3 H, --OCH.sub.3, 
--CH.sub.3, --C.sub.2 H.sub.5, --F, --Cl, --Br, --I, --NR.sub.7, 
--NHCOR.sub.7, --OH, --O, --SR.sub.7, --OR.sub.7, --OCOR.sub.7, 
--NO.sub.2, --COOH, --COOR.sub.7, --COR.sub.7, --CHO, and --CN, wherein 
R.sub.7, is a C.sub.1 -C.sub.8 alkyl, aryl or arylalkyl group. 
Furthermore, the fraction of rings containing at least one R.sub.1, 
R.sub.2, R.sub.3, or R.sub.4 groups as --SO.sub.3, --SO.sub.3 H--, R.sub.7 
SO.sub.3, or --R.sub.7 SO.sub.3 H can be varied from a few percent to one 
hundred percent. The solubility of the sulfonated polyaniline is varied by 
changing the degree of sulfonation. In fact the solubility of polyaniline 
is increased in basic aqueous solution by the presence of --SO.sub.3 H 
group on the phenyl rings. Also the oxidation state of the polymer and the 
degree of sulfonation can be independently varied. 
The synthesis of sulfonic acid ring-substituted polyaniline, or self-doped 
sulfonated polyaniline, is reported in an article entitled Synthesis of 
Self-Doped Conducting Polyaniline, Yue et al., J. Am. Chem. Soc, 
2800-2801, 1990 which is herein incorporated by reference. Briefly, 
sulfonated polyaniline is prepared by converting polyaniline to its more 
soluble nonconductive emeraldine base form and dissolving the base form in 
fuming sulfuric acid. Then, after 2 hours of constant stirring at room 
temperature, slowly adding the solution to methanol at a temperature of 
between 10.degree. C. to 20.degree. C. causes sulfonated polyaniline to 
precipitate. 
It is contemplated to be within the scope of the present invention to 
provide methods for preparing electrically conductive compositions of 
coated carbon particles by forming conductive polymer in a reaction 
mixture which additionally includes carbon particles. The amount of carbon 
particles in the reaction mixture is sufficient to provide each of the 
carbon particles with a coating of from approximately 5 wt % to 50 wt % 
conductive polymer. As previously mentioned, the carbon particles are 
preferably in the form of discrete unaggregated particles. However, 
aggregates of carbon particulates are fully within the definition of 
carbon particles for purposes of the present invention. 
In accordance with the present invention, carbon particles having a coating 
of conductive polymer can be prepared utilizing in situ methods by forming 
conductive polymer in a reaction mixture which incorporates carbon 
particles in an amount sufficient to provide each of the carbon particles 
with a coating of from approximately 5 wt % to 50 wt % conductive polymer. 
Then separating the conductive polymer from the reaction mixture provides 
an electrically conductive composition. When polyaniline is the selected 
conductive polymer the coating process is accomplished by forming a slurry 
of deaggregated and wetted carbon particles in a reaction mixture of a 
solution of solvent, protonic acid, aniline, and other additives such as 
suitable oxidants. Preferably, the reaction mixture also includes 
dianiline in an amount sufficient to provide the desired polyaniline 
molecular weight according to known polyaniline synthetic methods. As 
conductive polyaniline forms it coats the surface of the carbon particles, 
slowly precipitating a thin, adherent conductive coating. Typically the 
polymerization process occurs at temperatures between 0-80.degree. C. Once 
collected and washed the coated particles are suitable for incorporating 
into a suitable resin or matrix material as filler material, forming a 
conductive polymeric composition. 
A variety of protonic acids are suitable for forming acidic solutions 
and/or protonating polyaniline and include the aforementioned protonic 
acids useful in polyaniline synthesis and doping nonconductive polyaniline 
to form conductive polyaniline. Advantageously, protonic acids having 
surfactant properties are useful for prewetting and deaggregating carbon 
black. Thus, these surfactant protonic acids combine in their function as 
a surfactant and reactive acid in the above-described process. As 
previously mentioned, protonic acids belonging to this general class of 
compounds include decyl diphenylether disulfonic acid and decylphenylether 
disulfonic acid. Similarly, a variety of oxidants are suitable for 
incorporating into the reaction mixture and include ammonium persulfate, 
inorganic chlorates, inorganic chromates, and peroxides. 
Alternatively, carbon particles can be coated with conductive polymer by 
first forming a mixture of deaggregated carbon particles in a solution of 
polymer and then causing the polymer to precipitate onto the carbon 
particle by adding water or other non solvent for the polymer to the 
mixture. The coated carbon particles are then suitably collected, washed 
and dried. Typically, when polyaniline is the polymer of choice, the 
solution of polymer is a solution of free-base polyaniline in its undoped 
form. Accordingly, following the coating step the coated particles are 
converted to a conductive form by generating a coating of conductive 
polymer. This doping step is accomplished by forming a slurry of the 
coated carbon particles and aqueous solution of dopant. Suitable dopants 
are those protonic acids already mentioned which are useful in the 
synthesis of polyaniline. 
A preferred method for coating carbon particles with polyaniline includes 
first deaggregating carbon particles by stirring carbon particles in a 
suitable aqueous surfactant to form a slurry of carbon particles. Suitable 
surfactants include any of a variety of ionic and nonionic surfactants as 
known in the art. Preferred surfactants are those which are additionally 
suitable in the polymer synthesis and as dopants for the conductive 
polymer. These preferred surfactants include long chain alkyl substituted 
sulfonic acids such as those protonic acids having the formula 
##STR6## 
wherein G and G' are independently hydrogen, lower alkyl, octyl, nonyl, or 
saturated or unsaturated linear or branched decyl, dodecyl, tetradecyl, 
hexadecyl, or octadecyl groups. Protonic acids belonging to this general 
class of compounds have surfactant properties which aid in dispersing and 
deaggregating carbon particles. Exemplary protonic acids are selected from 
the group consisting of decyldiphenylether disulfonic acid and 
decylphenylether disulfonic acid. 
Subsequent process steps include pre-wetting carbon particles in an aqueous 
solution of protonic acid, combining aniline and dianiline with the wetted 
carbon particles, cooling the slurry and adding an appropriate oxidant. 
The polymer forms in the presence of the carbon particles and the polymer 
material actually coats the carbon black as the polymer forms. During the 
work-up step the carbon particles are collected, washed, and dried 
resulting in coated carbon particles having a coating of from about 5 wt % 
to about 50 wt % conductive polyaniline. 
An alternate method for coating carbon particles with conductive 
polyaniline includes dissolving soluble free base polyaniline in a 
suitable solvent such as N-methyl pyrrolidinone, formamide, 
dimethylformamide or dimethylsulfoxide, forming a slurry of carbon 
particles and then causing the dissolved polymer to precipitate onto the 
carbon particles. Typically water is added to the slurry to cause the 
precipitation, however, other nonsolvents for the polymer are effective 
for precipitating the polymer. The coated carbon particles are then 
dispersed in an aqueous solution of protonic acid as described above to 
produce the conductive acid-doped form of polyaniline. 
In accordance with the present invention, when self-doped sulfonated 
polyaniline is the conductive polymer of choice, the preferred method for 
preparing coated carbon particles involves dissolving sulfonated 
polyaniline in an aqueous base to form a polymer solution, adding carbon 
particles to form a slurry and then causing the polymer to precipitate 
onto the surface of the carbon particles. The preferred aqueous base is 
aqueous ammonia or ammonium hydroxide. However, other suitable aqueous 
bases include aqueous solutions of metal hydroxides having the formula: 
EQU M(OH).sub.n, 
wherein M is a metal having charge n, and n is an integer.gtoreq.1; 
compounds having the formula: 
EQU (NRR'R"R'")OH 
wherein R, R', R", R'" are independently H, alkyl, or aryl functionalities; 
and 
compounds having the formula: 
EQU NRR'R" 
wherein R, R', R" are independently H, alkyl, or aryl functionalities 
Typically, precipitating the polymer is accomplished by changing the pH of 
the polymer solution. More particularly, the pH of the aqueous system is 
caused to decrease causing the polymer to precipitate. Those skilled in 
the art will appreciate that adding a protonic acid to the aqueous system 
will cause the sulfonated polyaniline to precipitate. When aqueous ammonia 
or a volatile amine is the aqueous base, a preferred method for changing 
the polymer solution pH includes heating the polymer solution. This causes 
the base to leave the solution with a resulting drop in pH. Exposing the 
polymer solution to a vacuum aids the pH lowering process by causing the 
volatile amine. 
Alternatively, carbon particles having a coating of sulfonated polyaniline 
may be prepared using in situ methods similar to those discussed above. An 
exemplary method includes polymerizing amino-benzene sulfonic acid in 1 M 
HCL in the presence of a suitable oxidant and carbon black. As the polymer 
chain develops the polymer precipitates from solution onto the surface of 
the carbon black particles, forming a thin coating of conductive polymer. 
In accordance with the present invention and independent of the method 
selected for preparing coated carbon particles, carbon particles are 
preferably dispersed and relatively free of aggregates. Alternatively, 
aggregates which are present are small enough to maintain the structural 
and conductive characteristics of particles. Those skilled in the art will 
appreciate that once provided with a thin coating of conductive polymer, 
carbon particles having the least amount of aggregates are less likely to 
shear or break into a significant number of particles having exposed 
uncoated portions of carbon. The coating of conductive polymer protects 
the particle from conductive failure and provides other physical 
advantages. Accordingly, uncoated portions of aggregates or particles are 
preferably avoided. 
Suitable methods for deaggregating carbon particles include mechanical and 
ultrasonic dispersion techniques which are typically performed with the 
carbon black dispersed in aqueous systems containing a surfactant. Thus, 
for example, carbon particles having a coating of conductive polyaniline 
can be prepared by dispersing carbon particles in an aqueous solution of 
TRITON X-100 available from Rohm & Haas. Then, following the effective 
deaggregation of the carbon particles, a protonic acid, such as aqueous 
p-toluene sulfonic acid, aniline and/or dianiline and oxidant is charged 
into the dispersed carbon black mixture wherein the polymer forms and 
precipitates onto the carbon particles. 
In a preferred method for deaggregating and coating carbon particles 
utilizing methods which involve in situ polymerization processes, a 
disulfonated alkyl diphenyl ether provides both the surfactant properties 
and the acidic medium for the polymerization. An exemplary surfactant in 
this class of compounds is n-decyldiphenyl ether disulfonic acid, 
available from PILOT Chemical Co. This compound has two sulfonic acid 
groups per molecule and at least one ten member hydrocarbon chain per 
molecule. 
In accordance with the present invention, when coated carbon particles are 
prepared by polymerizing aniline in the presence of carbon particles, the 
coated carbon particles generally have a greater conductivity than 
precipitating free-base polyaniline onto carbon particles from a solution 
of the polymer. Moreover, when free-base polyaniline is precipitated onto 
carbon particles from a solution of polyaniline the conductivity of the 
resulting coated carbon particles is greater than the conductivity of 
material formed by merely combining neat conductive polyaniline and carbon 
particles and pressing the combination into a pellet. This phenomenon 
indicates that the greatest interaction between the polymer and the carbon 
particle occurs when the carbon is coated during the polymerization 
reaction. Similarly, a greater physical, chemical and electrical 
interaction between the conductive polymer and the carbon particle occurs 
when the polymer is precipitated onto the surface of carbon as compared to 
merely mixing conductive polymer and carbon particles. 
In view of the greater physical and chemical interactions which develop 
between the conductive polymer coating and carbon particle formed by in 
situ polymerization techniques, in situ preparation methods are preferred. 
Additionally, when highly structured dendritic forms of carbon black are 
utilized, in situ polymerization techniques tend to preserve the fine 
tree-like structure in the final filler material. This is believed to 
occur because the polymer actually grows on the surface of the fine 
structure as opposed to being quickly adsorbed by precipitation 
techniques. The slow deposition of polymer during in situ polymerization 
coating methods results in a more orderly polymer. Since ordering in 
conductive polymers is directly related to increased conductivity, the in 
situ polymerization deposition results in a higher bulk conductivity of 
the carbon particles. Furthermore, the in situ polymerization methods 
directly provide doped conductive polyaniline coating. This is in contrast 
to coatings formed during solvent precipitation methods which require 
further doping procedures in order to regenerate the conductive form. 
These final doping procedures frequently do not form fully doped polymer 
to provide maximum conductivity for the composition. 
As mentioned above, the protonated conductive form of polyaniline 
incorporates a counter-ion which is typically supplied by the acid 
utilized in the polymerization process or by the protonic acid utilized 
for converting the free base polyaniline to the protonated polyaniline. 
Connected with the choice of counter-ion of the conductive acid form is an 
associated conductivity of the polyaniline. However, surprisingly, the 
conductivity of carbon particles having a coating of conductive 
polyaniline does not necessarily parallel the performance of the 
conductive polymer alone. For example, polyaniline mesylate has a 
conductivity of approximately 10-20 S/cm and polyaniline tosylate has a 
conductivity of approximately 3 S/cm. Conversely, carbon particles having 
a coating of approximately 20 wt % polyaniline tosylate formed in situ 
during the aniline polymerization in accordance with the present invention 
have a conductivity of about 30 S/cm. Carbon particles having a coating of 
approximately 20 wt % polyaniline mesylate have a conductivity of about 24 
S/cm. Thus, by selectively choosing the counter-ion associated with 
conductive polyaniline, it is possible to tailor the conductivity of the 
resulting coated carbon particle. 
In accordance with the present invention the amount of conductive polymer 
formed on the surface of each carbon particle is preferably the minimum 
amount necessary to provide a thin coating. Those skilled in the art will 
appreciate that less conductive polymer is necessary to provide a thin 
coating on each particle of a relatively low surface area conductive 
carbon than the amount necessary to provide a thin coating on each 
particle of relatively high surface area carbon. In fact, the weight 
percent of conductive polymer to the total weight of the coated particle 
can vary from perhaps 5% to 50% or even higher. However, excessively thick 
coatings may detract from the desirable properties of the carbon. Thus, 
carbon particles having a surface area of about 250 m.sup.2 /gm (XC-72 
from Cabot Corp.) demonstrate good physical properties when provided with 
a thin conductive polymer coating which is approximately 20% of the weight 
of the total particle. However, carbon particles having a surface area of 
about 1000 m.sup.2 /gm (XE-2 from Degussa Corp.) are not well coated at 
this percentage because of their much higher surface area. In the case of 
carbon particles having a surface area of 1000 m.sup.2 /gm a coating 
weight which is equivalent to the weight of the carbon particle provides 
adequate coverage. 
Molecular surface area calculations can be performed to estimate the amount 
of polymer required to cover carbon particles having any given surface 
area. However, the results are only a guide due to the assumptions which 
go into the calculations. Another technique for measuring the quality of 
the polymer coating involves pressing a pellet of coated carbon particles 
after heating the coated carbon particles to 160.degree. C. for 30 
minutes. If a pellet forms by pressing at approximately 10,000 psi and the 
pellet is not easily destroyed by handling, then the quality of the 
coating is indicated as good. Pure carbon is not pelletized under these 
conditions. 
The above-described evaluation technique is additionally useful for testing 
the conductive composition of the present invention for its heat 
stability. This is particularly important for compositions used as filler 
in polymers exposed to high temperature environments. For example XE-2 
carbon particles having a surface area of about 1000 m.sup.2 /gm with a 20 
wt % coating will form a pellet at room temperature. This pellet is stable 
to mechanical manipulation. However, if the coated carbon is heated to 
160.degree. C.-200.degree. C. for 30 minutes and then pressed into a 
pellet, the pellet cracks easily and has little physical integrity. 
Apparently, the coating sinters at high temperatures and pools into carbon 
particle pores, thus reducing the amount of polymer on the exterior 
surfaces of the particle. However when these high surface area carbon 
particles are coated to a 50 wt % coating, the resulting conductive 
composition forms a strong pellet when subjected to the same conditions. 
It should be noted that even at these high coating levels the amount of 
conductive polymer in the composition is still substantially less than 
that typically used in a battery composition. 
Those skilled in the art will recognize that the above described 
conductivity properties of coated carbon particles formed in accordance 
with the present invention indicate the presence of significant 
interactions between the conductive polymer and the carbon particles. That 
is, the overall conductivity of the electrically conductive compositions 
of the present invention is clearly a function of the combination of 
conductive polymer coating and the carbon particles. If presynthesized 
conductive polyaniline tosylate is merely mixed with carbon particles at a 
ratio of 20 wt % polymer and 80 wt % carbon particles the conductivity is 
only about 13 S/cm. This is notably less than the 30 S/cm associated with 
carbon particles having a coating of polyaniline tosylate formed during 
the actual polymerization of aniline. This is further evidence of the 
interaction between the conductive polymer coating and the carbon 
particles. 
Those skilled in the art will appreciate that in addition to being 
dependent upon the amount and type of conductive polymer coating on the 
surface of the carbon particles, the conductivity of the compositions of 
the present invention is dependent upon the shape, size and morphology of 
the carbon particles. As discussed above, more highly structured graphitic 
carbon particles having dendritic shapes and high surface area are 
typically the most conductive forms. Similarly, coated carbon particles 
prepared from the more conductive forms of carbon particles is typically 
more highly conductive than filler prepared from particles having little 
structure and low graphitic content. 
The following examples are offered as being illustrative of the principles 
of the present invention and not by way of limitation. 
EXAMPLE 1 
Carbon black was dispersed, deaggregated and coated using in situ 
polymerization techniques and a dispersing surfactant which is also a 
suitable dopant for polyaniline. The dispersing and coating procedure was 
as follows. A solution of 0.73 grams of dianiline in 10.6 mL acetic acid 
was charged into a 2 L reaction flask. Then 64 grams of XE-2 carbon black 
was wetted with 16 mL acetic acid followed by the addition of 370 mL of 
water. 
After the carbon black was wetted by the acetic acid/water solution it was 
combined with 10.7 grams aniline and 270 mL of 1 N decyldiphenylether 
disulfonic acid (CALFAX 10LA--40 from PILOT Chemical Co.) and charged into 
the 2 L reaction flask. The mixture was agitated for 1 hour and a first 
sample was taken for particle size analysis. After 1.5 hours of agitation 
a second sample was taken. Then an ultrasonic probe was immersed in the 
mixture. Samples were intermittently taken for particle size analysis over 
a 4.5 hour period of time. During this time the average particle size 
remained between 0.13-0.15 microns. 
Following the above described dispersing step, 25.4 grams of ammonium 
persulfate was added to the flask over a 20 minute period while 
maintaining the temperature of the flask contents at 5.degree. C. After 20 
minutes of stirring 5 grams of sodium sulfite in 25 mL of water was added 
to the flask. A particle size analysis of the coated carbon black before 
filtering the coated particles indicated that the particles had an average 
size of 0.41 microns. The coated particles were then collected by both 
filtration and centrifugation and washed with acetone through a buchner 
funnel filter cake. The above procedure illustrated the successful 
preparation of carbon particles which were dispersed and coated using the 
same disulfonic acid. 
EXAMPLE 2 
Conductive polyaniline coated carbon particles were prepared according to 
the following procedure. XE-2 carbon filler material was pre-wet by adding 
640 grams of the carbon particles to 159 mL of acetic acid followed by the 
addition of 8.7 L of deionized water. The slurry of carbon particles, 
acetic acid and water was stirred until the carbon particles were well 
dispersed and wet. 
In a separate reaction container equipped with an ice bath, nitrogen inlet, 
solids addition funnel and condenser/outlet bubbler, 7.30 grams of 
dianiline was dissolved in 106 mL of acetic acid. Then 2.7 L of 1 N 
p-toluene sulfonic acid monohydrate and 106.62 grams of aniline were added 
to the dianiline solution. Finally the slurry of acetic acid, water, and 
carbon was added to the dianiline, aniline and p-toluene sulfonic acid 
monohydrate solution while rinsing the slurry container with deionized 
water. This reaction mixture was cooled to 5.degree. C. by maintaining an 
external dry ice bath between -5.degree. C. and -10.degree. C. 
Then a total of 253.78 grams of ammonium persulfate was added gradually to 
the cooled reaction mixture while maintaining the reaction mixture at 
5.degree. C.-10.degree. C. Once all the oxidant was added the reaction 
mixture was stirred for 20 minutes at 5.degree. C.-10.degree. C. After the 
20 minute stirring period, a solution of 50.28 grams of sodium sulfite 
(Na.sub.2 SO.sub.3) in 250 mL of deionized water was added to the reaction 
mixture and stirred for 10 minutes. 
To work up and recover the conductive polyaniline coated carbon particles, 
the solids were retrieved from the reaction mixture by filtering the 
product through a buchner funnel using #2 filter paper. The resulting 
filter cake was rinsed with 2 L of aqueous 1.0 N p-toluene sulfonic acid 
solution, 2 L of deionized water, 2 L of isopropyl alcohol, and 43 L of 
acetone. The rinsed solid product was then dried in a vacuum oven under 
full vacuum at 50.degree. C. 
EXAMPLE 3 
A thin coating of self-doped sulfonated polyaniline was formed onto the 
surface of highly dendritic carbon black particles according to the 
following procedure. First, 0.30 grams of sulfonated polyaniline were 
stirred in 3.0 mL of concentrated (28%) aqueous ammonia. After the 
sulfonated polyaniline was completely dissolved in the ammonia, 1.2 grams 
of dispersed XE-2 carbon black and 30 mL of aqueous ammonia were added to 
the ammonia and sulfonated polyaniline solution and stirred until the 
carbon black was well dispersed. 
Heat was added to the carbon black, ammonia and sulfonated polyaniline 
system until the temperature reached 60.degree. C.-70.degree. C. and a 
vacuum was applied to the system. Thus, the ammonia was driven from the 
water, reducing the pH and causing the sulfonated polyaniline to 
precipitate onto the surface of the carbon black particles. The pH dropped 
to between 7 and 8. 
Finally, the coated carbon black particles were collected by filtering and 
then washed with a solution of water, isopropyl alcohol, and acetone. The 
final coated carbon black was heated and oven dried to provide carbon 
particles having a coating of sulfonated polyaniline. A pellet weighing 
0.152 grams and having a thickness of 1442 microns was prepared and its 
conductivity determined using a standard 4 point probe conductivity 
measuring technique. The measured conductivity was 23.4 S/cm. 
EXAMPLE 4 
In order to test the thermal stability and physical integrity of a 
composition of the present invention, a sample of XC-72 carbon from Cabot 
Corp. was coated with conductive polyaniline according to the method 
described in Example 1. Then a pellet was pressed from 0.2425 grams of the 
coated carbon in a pellet press at 9000 psi to give a disk having a 
thickness of 2054 microns. The conductivity of the pellet was determined 
to be 12.4 S/cm using a Loresta 4-point probe conductivity/resistance 
meter. A gram of the conductive coated carbon particles from the same 
batch was then heated to 160.degree. C. in air in an oven for 30 minutes. 
A pellet having a thickness of 2333 microns was pressed from 0.2881 grams 
of this material. This pellet had good mechanical integrity and a 
conductivity of 12.0 S/cm as determined by the Loresta conductivity meter 
which corrects internally for variations in sample geometry. A third gram 
of the coated XC-72 carbon particles from the same batch was exposed to 
180.degree. C. for 30 minutes and then pressed to a pellet. This pellet 
had good mechanical integrity and a conductivity of 12.0 S/cm. A final 
gram of the above described conductive composition was exposed to 
200.degree. C. for 30 minutes and then pressed to a pellet at 9000 psi. 
This pellet had good mechanical integrity and a conductivity of 11.7 S/cm. 
This example demonstrates both the quality of the coating of an XC-72 
particle at 20 weight percent polymer and the excellent thermal stability 
of the polyaniline decyldiphenylether disulfonate coated composition. 
EXAMPLE 5 
XE-2 carbon particles, having a surface area of 1000 m.sup.2 /gm were 
coated with conductive polyaniline according to the method of Example 1. 
The resulting composition was pressed at 9000 psi to form a pellet. The 
conductivity of the pellet was determined to be 24.0 S/cm using a Loresta 
4-point probe conductivity/resistance meter. A second gram portion of the 
above described composition was heated to 160.degree. C. in air in an oven 
for 30 minutes. A pellet was pressed from a portion of this material after 
it had cooled to room temperature. The pellet had a conductivity of 21.5 
S/cm but cracked during testing of the conductivity. Portions of the same 
coated carbon particles treated at 180.degree. C. and 200.degree. C., 
which were pressed into pellets behaved similarly. 
EXAMPLE 6 
XE-2 carbon particles from Degussa Corporation having a surface area of 
1000 m.sup.2 /gm were coated with conductive polyaniline according to the 
method of Example 1. However, the coating process differed from that of 
Example 1 in that the conductive polymer coating represented 50 weight 
percent of the composition. The resulting conductive composition was then 
treated according to the procedures outlined in Example 5. The pellet, 
which was formed without a heat treatment had a conductivity of 8.1 S/cm. 
The pellet which was formed following a 160.degree. C. heat treatment had 
a conductivity of 4.5 S/cm and good mechanical integrity. Finally, the 
pellets which were formed following 180.degree. C. and 200.degree. C. 
treatments had good mechanical integrity and conductivities of 4.8 S/cm 
and 5.3 S/cm respectively. From the foregoing description it is clear that 
carbon particles having surface areas in the range of 1000 m.sup.2 /gm are 
sufficiently coated with 50 wt % conductive polymer. 
EXAMPLE 7 
High surface area carbon particles (XE-2) were coated with conductive 
polyaniline according to the procedure of Example 1 except that toluene 
sulfonic acid was utilized instead of decyldiphenylether disulfonic acid. 
The resulting conductive composition has a carbon particle coating weight 
of 20 wt % conductive polymer. Samples of this composition were treated 
and formed into pellets as described in Example 5. The pellet which was 
formed without heat treatment had a conductivity of 19.23 S/cm. Pellets 
prepared from the conductive composition and exposed for 30 minutes at 
160.degree. C., 180.degree. C., and 200.degree. C. showed conductivities 
of 24.3 S/cm, 18.8 S/cm, and 22.3 S/cm respectively. However, all of the 
pellets prepared from the heat aged samples cracked readily. The results 
of these experiments demonstrate that high surface area carbon particles 
should be coated with larger than 20 wt % polyaniline tosylate in order to 
have thermal stability. 
EXAMPLE 8 
The following example demonstrates the utility of an acidic dopant which 
can also serve as a surfactant for dispersing and deaggregating carbon 
particles. The carbon particle deaggregation step includes preparing a 
solution of 0.73 grams of p-dianiline in 10.6 mL of glacial acetic acid 
and charging this solution into a 2000 mL round bottom flask equipped with 
a teflon paddle mechanical stirrer, a thermometer, and N.sub.2 atmosphere. 
This was n-decyldiphenylether disulfonic acid solution to the round bottom 
flask. Then 10.7 grams of aniline were added to this solution. Then 64 
grams of carbon (Black Pearl 2000, Cabot Corporation) were wetted with 16 
mL of acetic acid followed by slowly adding 870 mL of water to form an 
aqueous carbon black slurry. This slurry was added to the 2000 mL reaction 
flask and rinsed in with 100 mL of deionized water. Agitation was 
continued under a N.sub.2 blanket. After 5 days of agitation the 
aggregates of carbon particles had broken down to a median particle size 
of 0.15 microns as measured by a sedimentation type particle size 
analyzer. 
EXAMPLE 9 
The procedure of example 8 was repeated except that a 1.0 N solution of 
p-toluene sulfonic acid was used instead of the 1.0 N solution of 
n-decycldiphenylether disulfonic acid. This mixture was agitated for 14 
days. After 14 days aggregates of carbon were still visible to the naked 
eye indicating poor dispersing ability of the p-toluene sulfonic acid as 
compared to the n-decyldiphenylether disulfonic acid described in Example 
8. This experiment demonstrates the superior ability of 
n-decyldiphenylether disulfonic acid to disperse and deaggregate carbon 
particles. 
EXAMPLE 10 
An electrically conductive composition of carbon particles having a coating 
of sulfonated polyaniline was prepared by dissolving 0.30 grams of 
sulfonated polyaniline in 3 mL of 30% aqueous ammonia to give a dark blue 
solution. This solution was added to 1.2 grams of deaggregated XE-2 carbon 
particles slurried in 30 mL of 30% aqueous ammonia. This mixture was 
heated at 60-70.degree. C. for 3 hours under approximately 28 inches of 
vacuum. The resulting slurry of carbon particles having a coating of 
sulfonated polyaniline was then filtered and washed with water. The water 
wash was slightly brown. This was followed by washes with isopropyl 
alcohol and acetone. These washes were clear. The carbon powder was dried 
overnight under vacuum at 50.degree. C. A pellet pressed from 0.1518 grams 
of the powder had good mechanical integrity and a conductivity of 23.4 
S/cm. 
EXAMPLE 11 
An electrically conductive composition of the present invention was 
prepared by causing presynthesized polyaniline to precipitate onto the 
surface of carbon particles according to the following procedure. A 
solution of 1.07 grams of polyaniline free-base in 10 mL of 
N-methylpyrrolidinone was prepared, followed by the addition of 5.35 grams 
of XE-2 carbon black, forming a paste. 75 mL of N-methylpyrrolidinone was 
added to the paste and the resulting slurry was stirred until the carbon 
was wetted. Then 50 mL of methanol was added dropwise to the slurry 
followed by 100 mL of water which was also added dropwise. At this point a 
small sample of the slurry was collected and allowed to settle. The 
supernatant was colorless indicating that the polymer had been adsorbed 
onto the surface of the carbon. The coated carbon particles were then 
filtered on a buchner funnel. The filter cake was then dispersed in 400 mL 
of aqueous 1.0 N p-toluene sulfonic acid with vigorous stirring for 30 
minutes. This slurry was then filtered and the filter cake was washed with 
1.0 N p-toluene sulfonic acid, isopropyl alcohol, and finally with 
acetone. The filtrate was colorless. The filter cake was broken-up, placed 
in a vacuum oven and dried overnight at full vacuum and 50.degree. C. A 
pellet pressed from this coated powder had a conductivity of 19.7 S/cm. 
One particularly surprising result of the coating of carbon particles with 
conductive polyaniline is that the conductive polyaniline is stabilized by 
the carbon with respect to loss of conductivity by thermal degradation. 
For instance a pellet pressed from polyaniline n-decyldiphenylether 
disulfonate has a room temperature conductivity of 1.2 S/cm. However, a 
pellet pressed from polyaniline n-decyldiphenylether disulfonate that had 
been heated at 160.degree. C. in air for 30 minutes is only 0.20 S/cm. 
Similar treatment at 180.degree. C. produces a conductivity of 0.19 S/cm 
while 200.degree. C. gives 0.052 S/cm and 220.degree. C. gives 0.0005 
S/cm. Thus the conductivity falls substantially between 180.degree. and 
200.degree. C. (The drop between room temperature and 160.degree. C. is 
related to loss of water of hydration and not substantially to thermal 
degradation). However similar treatment of carbon which is coated with 
polyaniline n-decyldiphenylether disulfonate shows the following 
conductivities. At room temperature, 12.4 S/cm; at 160.degree. C., 12.0 
S/cm; at 180.degree. C., 12.0 S/cm; at 200.degree. C., 11.7 S/cm; and at 
220.degree. C., 7.85 S/cm. (The reading of 7.85 S/cm corresponds to the 
reading obtained if the coated carbon is treated with aqueous base to 
generate the non-conductive form of polyaniline). 
Thus, with the conductive polymer coated onto carbon there is no 
substantial drop in conductivity until the dwell temperature reaches 
220.degree. C. This is important because the processing of plastics into 
which conductive polymer or conductive polymer coated carbon might be 
placed as filler often requires temperatures in the range of 200.degree. 
C. or even higher. However the dwell times during processing are generally 
on the order of a few seconds to a few minutes. Thus the conductive 
polymer coated on carbon has a better chance of retaining its conductivity 
than would be expected on the basis of the thermal stability of the 
conductive polymer alone. 
While the invention has been disclosed in this document by reference to the 
details of preferred embodiments and examples of the invention, it is to 
be understood that this disclosure is intended in an illustrative rather 
than in a limiting sense, as it is contemplated that modifications will 
readily occur to those skilled in the art, within the spirit of the 
invention and the scope of the claims which follow.