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Preparation, surface chemistry, and electrical conductivity of novel silicon carbide/polypyrrole composites containing an anionic surfactant.

INTRODUCTION

Silicon carbide (SiC) is a wide band gap semiconductor with high physical and chemical stability, which makes it a very promising material for electronic devices in high temperature, high power, and high frequency applications [1]. SiC technology has made tremendous strides in the past several years with a variety of potentially viable devices [2]. SiC is also used as a filler in polymer matrices for the preparation of composite materials [3, 4]. Submicro- and nano-particles of SiC as filler have improved the wear resistance of thermoplastic matrices like high density polyethylene, polytetrafluoroethylene, nylon, and polyetheretherketone [5, 6]. SiC is also a very promising material for optical applications, where the surface composition is crucial and it is expected to have an important effect on the dispersion of SiC particles. With this objective, several studies were undertaken with a specific focus on the behavior of SiC nano-particles in aqueous [7, 8] or organic solvents [9]. In most cases, adding surfactants was necessary for obtaining a stable liquid-phase suspension [10, 11].

[FIGURE 1 OMITTED]

A new type of conducting material can be prepared by modification of SiC particles with a conducting polymer, for example, polypyrrole or polyaniline. These composites can be used as fillers for modifying the conductive and the anti-abrasion properties of conventional insulating polymer matrices such as polyethylene and polypropylene.

Polypyrrole (PPy) (see chemical structure in Fig. 1) is an intrinsically conducting polymer with good physical and chemical properties, high electrical conductivity and environmental stability. As its applications are limited to problems associated with processability and mechanical properties, various copolymers, blends with commercially available polymers, or composites with inorganic materials were formed to improve its properties. These combined materials offer better mechanical properties, stability, and processability. Armes et al. [12] prepared colloidal silica/conducting polymer composites by the in situ deposition of a thin coating of chemically synthesized PPy onto monodispersed silica particles about 1 [micro]m in diameter. Another study of Gangopadhyay and De [13] reviewed the synthesis, characteristics, and applications of "inorganic in organic" systems using different intrinsically conductive polymers as modifiers for nano-sized metals, oxides, silica, and other inorganic materials.

Though conductive polymers can indeed be used to modify materials properties, this modification can be optimized by the use of surfactants during the in situ synthesis of conductive polymers such as PPy. Recently, Omastova et al. [14, 15] have shown that composition, structure, and conductivity of PPy can be tuned by the choice and the initial concentration of a series of surfactants. Generally, the addition of anionic surfactants into the polymerization mixture during pyrrole synthesis improves the electrical conductivity, thermo-oxidative, and hydrolytic stability of PPy due to incorporation of a bulky hydrophobic component into the PPy chains [14]. The anionic part of the surfactant is incorporated into the PPy chains similarly to the anion derived from the oxidant, and can be considered as a codopant (Fig. 1). Boukerma et al. [16] stressed, more specifically, the important role of anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in modifying the surface chemical composition of PPy. This surface/interface study highlighted the impact of surfactant on both the bulk and surface chemical composition of PPy. Conductivity of AOT-containing PPy exhibited an optimal value which was obtained at an initial pyrrole/AOT molar ratio = 7. Examination by X-ray photoelectron spectroscopy (XPS) of the PPy surfaces has shown that at higher initial AOT concentration (pyrrole/AOT molar ratio lower than 7), the aliphatic and ester carbon atom types (from AOT) dominated at the surface of the particles, which rendered these hydrophobic chains as steric barrier for the electrical charge transport between PPy powder particles.

The aim of this work is to explore the possibilities offered by the use of surfactants to tune and optimize the surface/interface and conductive properties of SiC/PPy composites. We used [alpha]-SiC for the preparation of the conductive composites. SiC was suspended in aqueous solutions of dodecylbenzenesulfonic acid, an anionic type of surfactant, and then in situ chemical oxidative polymerization of pyrrole followed. Investigation of morphology and conductivity of such composites is a continuation of the study conducted by Omastova et al. [17], where submicroparticles of [alpha]-SiC particles were covered only with PPy without any other additives. The physicochemical properties of the composites prepared in the presence of anionic surfactants were examined by the determination of the ash content (bulk organic content of the composites), scanning electron microscopy (surface morphology), conductivity measurements, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy (surface chemical composition).

EXPERIMENTAL

Materials

Pyrrole (Py) (Sigma-Aldrich, Germany) was purified by distillation at reduced pressure and stored at 4[degrees]C before use. The oxidant, ferric chloride (Fe[Cl.sub.3], Lachema, Czech Republic), surfactant dodecylbenzenesulfonic acid (DBSA, Sigma-Aldrich) and [alpha]-SiC grade UF-25 (HC Starck, Germany) with a particle size of about 0.8 [micro]m and green density = 1.5-1.7 g [cm.sup.-3], were used as received.

SiC/PPy and SiC-DBSA/PPy Preparation

Five grams of SiC were dispersed in 550 ml of distilled water, with or without DBSA, and stirred 15 min; then the oxidant, Fe[Cl.sub.3], was added and the mixture was stirred for 30 min. Pyrrole was dissolved in 10 ml of water and added drop-wise into the reaction mixture, which was then stirred for another 30 min. The molar ratio Fe[Cl.sub.3]/Py was 2.3 according to Myers [18] and Armes [19]. The molar ratio Py/DBSA was varied from 2 to 20 in the starting solution. After 4 h. the SiC particles coated with PPy (SiC/PPy or SiC-DBSA/PPy) were filtered and rinsed several times with distilled water. Later, the composites were dried at 60[degrees]C at atmospheric pressure for 24 h. SiC composites contained from 5 to 30 wt% PPy. The prepared composites are abbreviated as SiC-DBSA/xPPy_y, where x means Py content used in modification and y represents the molar ratio Py/DBSA. Composites prepared without DBSA will be abbreviated as SiC/xPPy.

Synthesis of PPy

The anionic surfactant DBSA (4.9 g) was dissolved in 600 ml of distilled water and then 75.5 mmol (5.2 ml) pyrrole were added. The solution was stirred for 30 min. The Py/DBSA molar ratio was 5/1. Then 171.2 mmol (27.8 g) of the oxidant Fe[Cl.sub.3], dissolved in 400 ml of water, was inserted into the stirred mixture. The polymerization was carried out for 1 h at room temperature under moderate stirring. The precipitated PPy powder was filtered off, washed with water, and dried for 12 h in an oven at 60[degrees]C followed by 8 h in vacuum (20 kPa) at 60[degrees]C. The surfactant-containing PPy powder is abbreviated PPyCl-DBSA.

For comparison, chloride-doped PPy (PPyCl) was synthesized in similar conditions in the absence of any surfactant to serve as a control specimen.

Characterizations Techniques

The content of the organic component in SiC/PPy and SiC-DBSA/PPy composites was assessed by ash analysis. Samples were heated 30 min at 550[degrees]C and the PPy and PPy-DBSA amount was determined from the weight difference of the sample before and after burning. The sulfur content of the samples prepared in the presence of DBSA was determined according to the following procedure. The sample was burnt up in the oxygen atmosphere according to the Schoniger method [20]. Absorption solution contained 5 ml of distilled water and 1 ml of [H.sub.2][O.sub.2]. Platinum net was washed with 20 ml of isopropanol. As indicator, 2 drops of Thorin and 1 drop of methylene blue were added. The sample was titrated with 0.02 N Ba(Cl[O.sub.4])[.sub.2], until appearance of orange color. Using the dimethylaminobenzylidene rhodanine standard, which contains 24.26% sulfur, it was found that consumption of 1 ml of 0.02 N Ba(Cl[O.sub.4])[.sub.2] solution corresponds to 0.3788 mg of sulfur. From consumption of 0.02 N Ba(Cl[O.sub.4])[.sub.2] solution, the amount of sulfur (S) was calculated using the equation:

S = [[0.3788 x consumption(Ba(Cl[O.sub.4])[.sub.2])]/weight of sample] x 100. (1)

Direct current (DC) electrical conductivity of the SiC/PPy and SiC-DBSA/PPy composites powder was measured under 30 MPa pressure by the van der Pauw four contact method in a special polyetheretherketone (PEEK) cell. Tesla picoammeter BM 545 and Metra Blansko multimeter M1T 380 were used for current and voltage measurements, respectively.

Infrared spectra in the range of 400-4000 [cm.sup.-1] were recorded at 64 scans per spectrum at 2 [cm.sup.-1] resolution using a fully computerized Thermo Nicolet NEXUS 870 FTIR spectrometer with a DTGS TEC detector. Measurements of the powdered samples were performed ex situ in the transmission mode in KBr pellets. All spectra were corrected for the presence of moisture and carbon dioxide in the optical path.

The morphology of the SiC/PPy composites and untreated SiC particles was studied by scanning electron microscopy (SEM) with a HITACHI S-800 (Hitachi, Japan) microscope. SiC powder and SiC/PPy particles were mixed in isooctane and suspensions were dispersed using ultrasound. A drop of the SiC or SiC/PPy suspension was deposited onto an electrically ground sample holder using a double-sided conducting adhesive tape. After evaporation of isooctane, the samples were coated with vapor-deposited gold layer in order to achieve a good quality of images and resolution.

XPS signals were recorded using a VG Scientific ESCALAB 250 system equipped with a micro-focused, monochromatic A1 K[alpha] X-ray source (1486.6 eV) and a magnetic lens, which increases the electron acceptance angle and hence the sensitivity. An X-ray beam of 650 [micro]m size was used at 20 mA x 15 kV. The spectra were acquired in the constant analyzer energy mode with pass energy of 150 and 40 eV for the survey and the narrow regions respectively. Charge compensation was achieved with an electron flood gun combined with an argon ion gun. The argon partial pressure was 2 x [10.sup.-8] mbar in the analysis chamber. The Avantage software, version 2.20 (Thermo Electron), was used for digital acquisition and data processing. Spectral calibration was determined by setting the PPy N1s peak at 399.7 eV [21]. In the case of the untreated SiC substrate, the correction for negative charging effects was assessed by setting the C1s component due to a hydrocarbon contamination at 285 eV.

The surface compositions (in atomic %) were determined by considering the integrated peak areas of Si2p, C1s, N1s, C12p, and O1s and the respective sensitivity factors. The fractional concentration of a particular element A was computed using

%A = [[[I.sub.A]/[S.sub.A]]/[[summation]([I.sub.n]/[S.sub.n])]] x 100, (2)

where [I.sub.n] and [S.sub.n] are the integrated peak areas and the Scofield sensitivity factors corrected for the analyzer transmission, respectively.

RESULTS AND DISCUSSION

For the preparation of SiC/PPy composites, [alpha]-SiC mainly 6H polytype of SiC with two polar surfaces, that is, silicon atoms terminated and carbon atoms terminated surface, was used. After modification of the SiC particles by pyrrole polymerization, the content of the organic component was determined by ash analysis at 550[degrees]C. The use of classical elemental analysis was not possible because the SiC component did not burn up in the elemental analysis equipment. The sulfur content of the samples prepared using DBSA was determined as described in the Experimental section.

Table 1 shows the ash content and sulfur content of SiC samples modified by PPy with and without DBSA. When using low amounts of pyrrole for the modification of SiC surface, polymerization yield is low. The surface of SiC particles is not totally covered with the conductive PPy layer, and consequently the conductivity of these composites is low as will be show later. From our previous study [17] we know that the homogeneous and continuous coating of PPy on SiC surface is achieved at 15 wt% of pyrrole loading, corresponding to 13 wt% of PPy detected. In the next step, the reaction conditions for the composition containing SiC and 15 wt% of pyrrole were optimized by changing the Py/DBSA molar ratio. The amount of sulfur and conductivity of SiC-DBSA/15PPy composite were investigated. With increasing Py/DBSA molar ratio, the amount of ash content decreases at the same pyrrole loading. For Py/DBSA = 20, the ash content is 86.95 wt%, whereas for the Py/DBSA = 2 it decreased down to 69.52 wt%. The reason for the difference in ash content over 17 wt% is that part of the surfactant is built into the PPy structure, and this surfactant fraction increases with increasing DBSA concentration, as demonstrated from the sulfur content in Table 1. Indeed, for a molar ratio Py/DBSA = 20, the sulfur content is as low as 0.5 wt%, but it increased rapidly up to 2.1% (4-fold) with decreasing Py/DBSA molar ratio to 2. In the latter case, the anionic part of DBSA is built into the PPy structure as a codopant, and simultaneously a part of the surfactant is adsorbed on the particle surface [16].

For comparison, Table 2 shows the weight composition, electrical conductivity, and relative yield of pure PPyCl synthesized in water solution using Fe[Cl.sub.3] as the oxidant and of PPyCl-DBSA prepared in the presence of DBSA. A high sulfur amount, about 4.8 wt% detected in PPyCl-DBSA, together with increasing amount of carbon and decreasing nitrogen content when compared with weight composition of PPyCl, confirm that a part of the surfactant is built into the PPy structure. The presence of anionic surfactant influences also structure and morphology of PPyCl-DBSA, resulting in higher conductivity, 13 S [cm.sup.-1], compared with 5.8 S [cm.sup.-1], which is the conductivity of PPyCl.

Figure 2 displays the morphologies of SiC, and SiC/PPy composite prepared with and without the surfactant, revealed by SEM. The SiC particles are angular with sharp edges and flat surfaces (Fig. 2a). The surface of SiC coated with PPy is more rounded (Fig. 2b and 2c), and the typical PPy globular structure is visible on the surface of modified SiC particles. The differences in the morphology of the composite sample were macroscopically visible also after pyrrole polymerization, the original grey color of SiC changed to black.

Figure 3 compares the electrical conductivities of SiC/PPy and SiC-DBSA/PPy composites prepared using a Py/DBSA molar ratio of 10/1. The conductivity of unmodified SiC powder was also measured, but the value was lower than the detection limit of the equipment ([10.sup.-10] S [cm.sup.-1]). For SiC coated with a PPy amount lower than 30%, the conductivity of SiC-DBSA/PPy is significantly higher than the conductivity of SiC/PPy. Using 15 wt% Py for SiC modification in the presence of DBSA, conductivity of the resulting composite samples is 0.4 S [cm.sup.-1], while the composite prepared without DBSA shows a conductivity of only about 1.9 x [10.sup.-3] S [cm.sup.-1].

Figure 4a displays the infrared spectra of virgin SiC, of PPy-Cl/DBSA and of eight SiC-DBSA/15PPy composites prepared at different Py/DBSA molar ratios. The position of the band of the stretching vibrations of Si-C-O and Si-O-Si bonds [22] at 841 [cm.sup.-1] with a shoulder at 940 [cm.sup.-1] in the transmission spectra is practically unchanged in the spectra of SiC/PPy composites containing low amounts of PPy. The IR absorption bands for PPy were assigned according to the literature [14, 23, 24], namely the C-C stretching vibrations of the pyrrole ring at 1540 [cm.sup.-1], C-N stretching vibrations of the pyrrole ring at 1459 [cm.sup.-1], and a broad band at 1400-1200 [cm.sup.-1] with a maximum at 1308 [cm.sup.-1] attributed to C-H or C-N in-plane deformation vibrations. Their positions are slightly shifted in the spectra of KBr pellets relative to the spectrum of pure PPyCl, which indicates a more intimate interaction between SiC and PPy.

[FIGURE 2 OMITTED]

The presence of DBSA in the reaction mixture affects the spectra. In the spectra of SiC-DBSA/15PPy, we observe a small gradual shift of some bands with increasing amounts of DBSA (decreasing Py/DBSA molar ratio). The bands of C-C and C-N stretching vibrations in the pyrrole ring observed at 1548 [cm.sup.-1] and 1475 [cm.sup.-1] in the spectrum of SiC-DBSA/15PPy_20 are shifted to 1544 [cm.sup.-1] and 1455 [cm.sup.-1] for the spectrum of SiC-DBSA/PPy_2. The red shift of the first band is in accordance with the observed increase in the conductivity [14]. The broad band from 1400 [cm.sup.-1] to 1250 [cm.sup.-1], attributed to C-H or C-N in-plane deformation modes, is not influenced by the presence of DBSA. In the region from 1177 [cm.sup.-1] to 1168 [cm.sup.-1], we observe an increase of the absorption and a shift of the maximum going from the spectrum corresponding to the decrease of Py/DBSA molar ratio. It is connected with the band of S=O stretching vibration of DBSA present in this part of the spectrum. The presence of DBSA is also confirmed by another peak of S=O stretching vibration at 620 [cm.sup.-1] in the spectrum of SiC-DBSA/PPy_2.

[FIGURE 3 OMITTED]

The effects of the presence of DBSA in the reaction mixture are also shown in Fig. 4b, where the infrared spectra of virgin SiC, of SiC/15PPy composites prepared without any surfactant and with the surfactant using a molar ratio of Py/DBSA = 7 in the reaction mixture, and the spectrum of PPyCl are compared. Besides the already described red shift and increased intensity of the band at 1168 [cm.sup.-1], one can observe that the spectrum intensity of PPy prepared in the presence of DBSA is higher than without DBSA.

Figure 5 depicts survey scans of untreated SiC, SiC/15PPy, and SiC-DBSA/15PPy composites. The main Si2p, C1s, N1s, and O1s peaks are centered at ~100, 285, 400, and 532 eV, respectively. In the case of DBSA-containing composites, the characteristic S2p and S2s peaks of the surfactant (centered at approximately 168 and 231 eV, respectively) are readily detected. Contrary to SiC/15PPy, the C12p peak (~198 eV) from the chloride dopant is weak and almost disappears for SiC-DBSA/15PPy_5 (initial Py/DBSA [less than or equal to]5).

It is worthy to note that the addition of DBSA in the polymerization medium, even at the lowest DBSA content (molar ratio Py/DBSA = 20), yields an increase in the Nls/Si2p intensity ratio while the organic content of the composites is not changed dramatically. This is a qualitative indication that only the surface of SiC is extensively modified by PPy.

Table 3 shows the apparent surface chemical composition in at%. The carbon content increases on coating the SiC surface by PPy in the presence of DBSA as well as without. Silicon decreases with addition of PPy; the effect is emphasized when DBSA is added for the preparation of the composites. The nitrogen content increases with the mass loading of PPy. The effect of DBSA is positive for a Py/DBSA initial ratio [greater than or equal to]6.

[FIGURE 4 OMITTED]

Using the data reported in Table 3 and plotting the N/Si surface atomic ratio versus the Py/DBSA initial molar ratio, it is possible to determine the effective coating of SiC by PPy. Figure 6 shows that for a target PPy mass loading of 15 wt%, the use of DBSA even at the lowest ratio is positive. Indeed, all materials considered in Fig. 6 indicate an N/Si ratio higher than the N/Si ratio of DBSA-free SiC/15PPy, shown in Fig. 6 as reference line. However, there is a clear optimal value around 0.25 (Py/DBSA = 4) beyond which the N/Si value decreases. Most probably, as DBSA is incorporated into PPy adlayers, it induces a slight decrease in the N/Si value at high Py/DBSA initial ratio. When using a small amount of the surfactant for the composite preparation (Py/DBSA = 16.5 or 20), the N/Si value detected by XPS is close to that of surfactant-free SiC/15PPy composite.

[FIGURE 5 OMITTED]

The in situ synthesis of PPy in the presence of the surfactant using Fe[Cl.sub.3] as an oxidant results in the incorporation of chlorides and dodecylbenzosulfonate (DBS[A.sup.-]) anions as codopants. PPy doping can thus be determined by considering the (S+Cl)/N atomic ratios determined by XPS. This ratio for SiC-DBSA/15PPy is plotted versus the Py/DBSA ratio in Fig. 7. The ratio exceeds the 25-33% doping range known for PPy. This indicates that, as in the same way as in the case of PPy prepared in the presence of higher amounts of AOT, DBSA acts both as a codopant and a surfactant. Indeed, for the SiC/PPy composites, the Cl/N ratio is in the 24.4-32.5% range. For the SiC-DBSA/15PPy prepared with a pyrrole/DBSA ratio of 20 and 16.5, the doping by chlorides and sulfonates is 33 and 29% respectively. For the molar ratio Py/DBSA [less than or equal to]10, the ratio (S+Cl)/N exceeds the normal doping level of PPy, its values range from 38 to 63%. As for the DBSA-containing materials the Cl/N ratio is in the 3.6-19.2% range, it is clear that DBSA is incorporated into the PPy, where it compensate for the low chlorine content, as detected by XPS (Table 3). Therefore, in materials prepared using molar ratio pyrrole/DBSA [less than or equal to]10, the DBSA is also incorporated as a surfactant. This is in agreement with our previously published paper on PPy powder prepared in the presence of AOT [16]. The incorporation of DBSA as a surfactant has a consequence on the behavior of SiC/PPy composites in terms of their interaction with water (see next).

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

The conductivity of the SiC/PPy composites has been related to the PPy mass loading mentioned above. Conductivity is related to the actual surface chemical composition as determined by XPS. Figure 8 shows a plot of the electrical conductivity of SiC-DBSA/15PPy composites versus the ratio N/Si, taken as a chemical descriptor of the surface content of PPy. All surfactant-containing composites have a conductivity matching the plateau value, that is, about two orders of magnitude higher than that of the reference SiC/15PPy (1.9 x [10.sup.-3] S [cm.sup.-1]). Clearly, the electrical conductivity of the SiC/PPy composites can be intimately related to the presence of PPy at the surface, thus to the chemical composition of the outermost layers of the composites under test.

We have also investigated the interactions of SiC-DBSA/PPy particles with water at the macroscopic scale (Fig. 9). We found that they exhibited an extremely hydrophobic character in the sense that they floated on the water surface. In contrast, the DBSA-free particles flocculated in water. The photograph shown in Fig. 9 was taken 24 h after mixing both types of particles with water and despite this prolonged period; the SiC-DBSA/PPy_5 particles did not sediment.

The surfactant at the surface of SiC-DBSA/PPy, detected by XPS, imparts to these particles a very hydrophobic character due to the long dodecyl chains, as depicted schematically in Fig. 9d. Since the hydrophilic anionic head of this surfactant could act as a codopant for PPy, we suggest that the anionic head is "embedded" in or interacting with the PPy first adlayers, while the hydrophobic dodecyl chains create the free surface of the composites. SiC-DBSA/PPy particles containing hydrophobic surfactant chains on the surface are not wetted by water, and therefore such particles floating at its surface.

[FIGURE 9 OMITTED]

CONCLUSIONS

SiC/PPy-DBSA composites were prepared by chemical oxidative polymerization of pyrrole in the presence of SiC particles (800 nm in diameter) dispersed in an aqueous solution of DBSA. Fe[Cl.sub.3] was chosen as the oxidant. The composite with the highest conductivity (1.70 S [cm.sup.-1]) was achieved using a Py/DBSA molar ratio = 5 for the initial pyrrole polymerization.

The SEM study reveals that the morphology of the SiC/PPy composites differs from that of the untreated SiC particles. The infrared spectra suggest that the PPy coating does not alter the chemical structure of the underlying SiC substrate. SiC/PPy composites prepared in the presence of surfactants have almost the same percolation threshold of the conductivity as the DBSA-free composites, but they all exhibit a significantly higher conductivity by up to two orders of magnitude. The enhanced conductivity was interpreted in terms of higher nitrogen content at the surface of the particles and also of a slightly higher doping of PPy compared with the materials prepared in the absence of surfactant. At high initial concentrations of DBSA, the apparent doping of PPy far exceeded the reference range of 25-33% implying that DBSA acted both as a codopant and as a surfactant. This consequently imparted a pronounced hydrophobic character to the SiC/PPy-DBSA particles which can only float at the free surface of water and do not mix with it at all.

From the above results, it can be concluded that the anionic surfactants constitute important building blocks of novel PPy composites with a controlled surface chemistry and electrical conductivity. These properties are essential in designing conductive (nano) fillers based on PPy with a pronounced hydrophobic character which is of interest for mixing with conventional hydrophobic polymer matrices (e.g. polyethylene, polypropylene).

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Matej Micusik, (1) Maria Omastova, (1) Kada Boukerma, (2) Aurelie Albouy, (2) Mohamed M. Chehimi, (2) Miroslava Trchova, (3) Pavol Fedorko (4)

(1) Polymer Institute, Slovak Academy of Sciences, Dubravska cesta 9, 842 36 Bratislava, Slovakia

(2) Interfaces, Traitements, Organisation et Dynamique des Systemes (ITODYS), Universite Denis Diderot-Paris 7, CNRS (UMR 7086), 1 rue Guy de la Brosse, 75005 Paris, France

(3) Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic

(4) Department of Chemical Physics, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinskeho 9, 812 37 Bratislava, Slovakia

Correspondence to: M. Omastova; e-mail: upolmaom@savba.sk

Contract grant sponsor: Slovak Academy of Sciences and French CNRS through the French-Slovak bilateral Cooperation; contract grant numbers: 18183; Contract grant sponsor: Conseil Regional d'Ile-de-France; contract grant numbers: SESAME 2000 project; Contract grant sponsor: Scientific Grant Agency of the Ministry of Education of Slovakia and the Slovak Academy of Sciences; contract grant numbers: VEGA 2/4024/04; 1/2021/05; Contract grant sponsor: Grant Agency of the Academy of Sciences of the Czech Republic; contract grant numbers: A400500504
TABLE 1. Ash and sulfur content in SiC, SiC/PPy, and SiC-DBSA/15PPy
composites prepared using various pyrrole/DBSA molar ratios.

Sample Ash content (wt%) S content (wt%)

SiC 99.85 --
SiC/5PPy 98.39 --
SiC/10PPy 93.10 --
SiC/15PPy 86.39 --
SiC/30PPy 69.43 --
SiC-DBSA/15PPy_20 86.95 0.5
SiC-DBSA/15PPy_16.5 86.23 0.5
SiC-DBSA/15PPy_10 82.84 0.9
SiC-DBSA/15PPy_8 82.27 1.1
SiC-DBSA/15PPy_7 81.58 1.2
SiC-DBSA/15PPy_6 79.99 1.3
SiC-DBSA/15PPy_5 79.00 1.6
SiC-DBSA/15PPy_4 74.66 1.9
SiC-DBSA/15PPy_3 71.62 2.0
SiC-DBSA/15PPy_2 69.52 2.1

TABLE 2. Weight composition, electrical conductivity and relative yield
of PPy.

 Electrical
 Composition (wt%) conductivity Yield
Polypyrrole N C H S (S [cm.sup.-1]) (g/g of monomer)

PPyCl 15.23 53.50 4.00 5.8 1.16
PPyCl-DBSA 9.31 64.60 6.14 4.8 13 1.74

TABLE 3. Apparent surface compositions (in at%) of the SiC-DBSA/PPy
composites and of the reference specimens SiC, bulk Py-Cl and PPyCl-DBSA
powder, as determined by XPS.

Sample C Si N O Cl S

PPyCl 74.35 -- 12.42 9.81 3.42 --
PPyCl-DBSA 79.23 -- 11.71 6.08 2.33 0.65
SiC 47.31 34.73 -- 17.96 -- --
SiC-DBSA/15PPy_20 62.89 14.53 7.09 13.11 1.36 1.01
SiC-DBSA/15PPy_16.5 60.87 16.72 6.37 14.17 0.93 0.93
SiC-DBSA/15PPy_10 68.22 10.83 6.05 12.10 0.78 2.02
SiC-DBSA/15PPy_8 74.14 6.72 5.31 11.84 0.26 1.72
SiC-DBSA/15PPy_7 71.98 6.93 7.03 11.33 0.31 2.41
SiC-DBSA/15PPy_6 72.69 5.70 7.30 11.17 0.26 2.88
SiC-DBSA/15PPy_5 76.41 4.50 5.48 11.05 -- 2.55
SiC-DBSA/15PPy_4 77.57 3.52 5.10 11.58 -- 2.23
SiC-DBSA/15PPy_3 76.21 5.44 4.20 11.52 -- 2.63
SiC-DBSA/15PPy_2 72.56 6.19 3.90 13.67 0.28 3.40
SiC/5PPy 55.08 26.20 0.61 18.11 -- --
SiC/10PPy 61.84 18.20 4.09 14.87 1.00 --
SiC/15PPy 61.47 17.01 5.94 14.06 1.52 --
SiC/30PPy 74.32 2.98 12.64 5.95 4.11 --
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Author:Micusik, Matej; Omastova, Maria; Boukerma, Kada; Albouy, Aurelie; Chehimi, Mohamed M.; Trchova, Miro
Publication:Polymer Engineering and Science
Article Type:Technical report
Geographic Code:1USA
Date:Aug 1, 2007
Words:5286
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