Online Measured Electrical Conductance

Transcription

1 PRÜFEN UND MESSEN TESTING AND MEASURING Carbon nanotubes Electrical conductivity Online measurement Dispersion behavior Phase selective filler distribution The mechanism of CNT dispersion in rubber matrices was studied by the analysis of the morphological development on macro- and microscale by optical and electron microscopy as well as atomic force microscopy. The results from the morphological assessment were correlated to the time dependent electrical conductance measured directly during the mixing process. It becomes obvious that the conductancetime curves measured during the mixing process of CNT-rubber compounds show basically the same course like for carbon black (CB) filled rubber mixtures. The time-dependent stages of the electrical conductance have been correlated to the degree of CNT dispersion, successfully determined by microscopical methods. The investigation shows that CNT can be controlled introduced into rubber matrix materials using the method of online measured electrical conductance during the mixing process. Mischprozessintegrierte Charakterisierung des Dispersionsverhaltens von Carbon Nanotubes in Kautschukcompounds durch Erfassung des Online-Leitwerts Carbon Nanotubes Elektrische Leitfähigkeit Online Messung Dispersionsverhalten Phasenselektive Füllstoffverteilung Der Mechanismus der CNT-Dispersion wurde durch die morphologische Analyse auf unterschiedlichen Längenskalen mittels Lichtmikroskopie, Atomic Force Microscopy (AFM) und Transmissionselektronenmikroskopie (TEM) visualisiert. Die Ergebnisse der morphologischen Untersuchungen wurden mit dem online erfassten zeitlichen Verlauf des elektischen Leitwerts korreliert. Es wurde deutlich, dass die für die Kautschuk-CNT-Compounds erfassten Leitwert-Zeit-Kurven prinzipiell den gleichen Verlauf aufweisen, wie für Kautschuk-Ruß-Systeme, obwohl sich beide Füllstofftypen maßgeblich hinsichtlich ihrer geometrischen Form unterscheiden. In beiden Prozessen wurde ein lokales Maximum des Online- Leitwerts erfasst. Online Measured Electrical Conductance In-Process Characterization of the Dispersion Behavior of Carbon Nanotubes in Rubber Compounds There is a wide range of potential applications for carbon nanotubes using their electrical, thermal and mechanical properties. A central hurdle is the hard dispersability of these new type of nanofiller into conventional polymers. CNT tend to form rope-like bundles due to their long aspect ratios (,000) and the strong anisotropic interactions between them []. Additionally, the bundles can be highly contiguous, making them difficult to disperse in both organic and aqueous media. In theory, compound properties, like e.g. stiffness, could be enhanced by a factor of ten or more by CNT. In practice, the manufactured materials are still far from approaching these values [2]. Poor dispersion leads to rope-like aggregates or bundles of nanotubes, which act as material defects instead of transferring load to the matrix polymer. That negatively affects the application properties, including electrical, optical and thermal characteristics. Numerous attempts have been made to develop an effective method for the discrete dispersion of CNT at high concentrations. These approaches have included the in situ polymerization [3, 4], chemical functionalization of the tube sidewalls [5-0] or spraying an aqueous solution of CNT onto a fine polymer powder []. Surfactants and macromolecules have also been used to coat the surfaces of the tubes [7, 2-5]. Among them direct dispersing of CNT in polymers by melt mixing process is a key method for the production of nanocomposites at a large scale [6-20]. In order to find an effective way to dispers CNT into polymer matrices by melt mixing, one has to understand the dispersion mechanism of CNT in polymer. A promising possibility to monitor the dispersion process of conductive filler is the use of the method of the online measured electrical conductance directly in the mixing equipment. The electrical conductance measured along the mixing time (online conductance) is a function of dispersion and distribution of electrical conductive filler as frequently discussed in our previous works with carbon black in conventional rubbers [2]. Knowledge about the mechanism and kinetics of filler dispersion is essentially useful for receiving tailor-made properties with minimal fluctuation. In the present work, using the method of online measured electrical conductance an attempt is made to characterize the CNT dispersion in CNT-rubber nanocomposites. Development in the morphology of nanocomposites, wetting behavior of CNT and mechanical properties of nanocomposites have been investigated in correlation with the online measured electrical conductance. The technological and material effects on the CNT dispersion/online conductance were studied. The phase specific spatial distribution of CNT in rubber blends using the new developed method based on thermogravimetric analysis (TGA) of bound rubber was evaluated. The success of the work in laboratory scale initiates the application of the method of the online conductance for monitoring the production of CNT nanocomposites in industrial scale. Authors H. H. Le, G. Kasaliwal, S. Ilisch, H.-J. Radusch, Halle (Saale) Corresponding author: Dr.-Ing. Sybill Ilisch Martin-Luther-Universität Halle-Wittenberg Zentrum für Ingenieurwissenschaften Hoher Weg Halle sybill.ilisch@iw.uni-halle.de 326 KGK Juni 2009

2 Experimental Materials and composite preparation Multiwalled carbon nanotubes (Baytubes- C50P, Bayer Material Science) with outer diameter and the length of 3-5 nm and -0 m, respectively, were used. Natural rubber (SMR 0, Astlett Rubber Inc.), styrene-butadiene rubber (SE-SLR 4400, Dow) and acrylonitrile-butadiene rubber (Krynac 34.35, Bayer) were used. In order to characterize the effect of the matrix polarity on the CNT dispersion, epoxidised natural rubber (ENR-25 and ENR-50, Weber & Schaer) with 25 mol % and 50 mol % epoxy groups, respectively, were used. For characterization of the effect of the matrix viscosity by keeping the same polarity, the natural rubber was masticated in a two roll mill for different periods of time. During the mastication process at room temperature, the rubber undergoes a chain scission, which results in a decrease of the molecular weight and viscosity [3-32]. The designation of the NR samples undergoing different mastication times is N0, N and N2. The torque of the raw rubbers measured in a rheometer can be used as a measure for estimation of the viscosity of the materials investigated (Table ). The CNT-rubber compounds and blends were prepared in an internal mixer (Rheocord 300 p, ThermoFischer) according to the formulation given in Table 2. In order to investigate the kinetics of the CNT dispersion, a model mixture of NR and CNT was prepared by keeping the mixing conditions unchanged (initial chamber temperature T A 25 C, rotor speed n 50 rpm, fill factor 0.6). The mixing time was varied by taking into account the electrical conductancetime characteristic as done in our previous work [23]. In order to characterize the technological effect on the online conductance, initial chamber temperature and rotor speed were varied systematically. Optical microscopy Optical microscopy (OM) has been used to characterize the CNT macrodispersion. This method was described for CB filled compounds by Leigh-Dugmore [33] and modified by us [22] With a special image analysis program one can calculate the area of larger CNT regions. The macrodispersion index D (Eq. ) was assessed as the amount of the non-dispersed agglomerates (A/A 0 ) with an average diameter larger than 6 m. A dispersion index of 00 % means, that no agglomerate size larger than 6 m could be found in the cut surface. From each sample six pictures were made and from each picture six image analyses were taken. D f AA 0 () is the volume fraction of the filler. f is a factor related to the effective volume of the filler. A f 0.4 has been proposed for CB by Medalia [34]. For CNT used in the present work we estimated f 0.25 by taking into account the morphological analysis of the TEM images of pure CNT. Atomic Force Microscopy (AFM) Morphological investigations were carried out by an atomic force microscope Q-Scope 250 (Quesant) operated in intermittent mode. The smooth surfaces of samples were prepared by a cryomicrotom HM 360 (Microm) at -20 C with diamond knife. Transmission Electron Microscopy (TEM) Microstructure was examined using a transmission electron microscope JEM 200 (Jeol). Ultrathin sections of each sample (ca. 00 nm) were prepared at -00 C from a bulk specimen using an ultramicrotome Ultracut E (Leica) with cryo-system FC6 (Leica). Measurement of the offline conductivity After mixing CNT filled materials were compression moulded and vulcanized at a temperature of 45 C to get thin sheets of one millimeter thickness. Circular samples with a diameter of.2 cm were cut from these sheets for the determination of the offline electrical conductivity C off. Offline conductivity measurements were performed at room temperature using the sandwich principle by means of a multimeter 2750 (Keithley). By this method the volume conductivity of the samples was measured as C off in ms/cm, normalized to a definite measured volume. Measuring equipment for the online conductance A conductance sensor has been installed in the chamber of the internal mixer to measure the electrical signal of the conductive mixture between the sensor and the chamber wall. The construction and position of the conductance sensor has been described in our previous works [26, 27]. Using this construction the online conductance C on of the material s volume placed stochastically in the electrical field between the electrodes was measured as C on in ms. A very good reproducibility of the electrical signal has been received for a number of conventional rubbers. Analysis of the rubber-cnt gel For the investigation of the rubber-filler gel, 0.25 g of each raw mixture was stored for seven days in 00 ml cyclohexane at room temperature. After four days the solvent was completely renewed. The rubber-cnt gel was taken out and dried up to a constant mass. The rubber content in the gel L SBR, L NR and L B(SBR/NR) as a measure for the wetting behavior of single rubber SBR, NR and 50/50 SBR/NR blend on CNT, respectively, was determined according to our previous work [30]. L B(SBR) and L B(NR) are the rubber part in the rubber-filler gel of the blend and their sum is L B(SBR/NR) according to Eq. 2. BSBRNR L ( / ) BSBR BNR t L ( ) t L ( ) t (2) L B(SBR) and L B(NR) were determined from L B(SBR/ NR) using thermogravimetric analysis (TGA) of the gel of the rubber blends according to our method [30]. The analysis was carried out by a thermo-balance TGA /SDTA 85 (Mettler-Toledo) in the temperature range between 30 C and 800 C with a heating rate of 20 K/min. The phase specific CNT distribution in 50/50 SBR/NR blend was calculated according to the following equations: R R BSBR ( ) BNR ( ) NR BSBR ( ) t L L t P SBR BNR ( ) t L L t P B B( SBR) B( NR) B R R t R t R t Rheometer torque of the raw rubbers at 90 C and 5 s - Rubber Torque (Nm) N0 0.4 N N ENR ENR SBR NBR Formulation of the investigated mixtures Ingredients Amount (phr) Rubber 00 Carbon nanotubes X Sulfur 2 Zinc oxide Stearic acid CBS f (3) (4) KGK Juni

3 PRÜFEN UND MESSEN TESTING AND MEASURING elasticity was characterized at low amplitudes. Results and discussion B R t R f Correlation between online measured electrical conductance and offline measured electrical conductivity at different mixing times for NBR with 5 phr CNT (a), and at different CNT contents at t 70 min (b); (T A 25 C, n 50 rpm, 0.6) B L L t BSBRNR ( / ) BSBRNR ( / ) (5) P R BSBR ( ) and R BNR ( ) are CNT amounts in the SBR and NR blend phase, respectively. t is the mixing time. R B f is the free CNT which is not BSBRNR ( / ) yet wetted by rubber at the time t. L P is the saturated rubber content in the gel of the blend [30]. Online conductance and macrodispersion index of NR-CNT compounds (N with 20 phr CNT, T A 25 C, n 50 rpm, 0.6) AFM-images of NR-CNT (N with 20 phr CNT). Samples taken at 3 min (a), 32 min (b) and 90 min (c) 2 Dynamic-mechanical analysis Dynamic-mechanical analysis (DMA) was performed by means of a mechanical spectrometer Eplexor 500 N (Gabo). Strain sweep measurements were carried out at room temperature and at a frequency of 0 Hz. The strain amplitude was varied in the range of 0.0 % 0 %. The specimens of size 25 mm 5 mm were stamped out from the crosslinked rubber sheets. The modulus of Correlation between the online measured electrical conductance and the offline measured electrical conductivity Figures a and b show the change of offline conductivity in comparison to the online conductance. It is well known that the offline conductivity has to be measured for a definite sample geometry keeping constant the temperature and the pressure. The CNT network in the sample is in a steady state during the measurement. Furthermore, before the measurement of the offline conductivity the sample must be vulcanized. It is worth to note that the change of the offline conductivity in the whole mixing period (Fig. a) is restricted on one decade. For some high-end applications even a small fluctuation like that can be essential. Thus, the result shows a big advantage of the online conductance measurement method which can monitor the small value scattering of the offline conductivity already in the stage of mixing. Compared to some thermoplastics filled with 4 phr CNT [35] the offline conductivity of CNT filled rubber prepared in the present work is rather low even at a CNT content of 5 phr (Fig. b). Correlation between online conductance and macrodispersion In Figure 2 an online conductance curve of CNT filled NR is presented. The curve shows a typical shape as received quite similar for CB filled rubbers [26]. The onset time t onset of the conductance is observed at about 3 min and the BIT at 32 min. During the mixing at different times samples were taken out and investigated by optical microscopy. In the OM images different CNT agglomerates can be observed (Fig. 2). The largest change of the size of CNT agglomerates is determined in the range between t onset and BIT. The macrodispersion index, a measure describing the change of the CNT agglomerate size, is determined from the OM images using Eq. and presented in Figure 2. As discussed in our previous works [23, 26] the macrodispersion and the online conductance correlate close to each other in the period between the t onset and BIT. After the BIT the macrodispersion increases insignificantly but the conductance is going on decaying gradually. As discussed before, the main reason for the decrease of conductance 328 KGK Juni 2009

4 is related to the distribution of small aggregates throughout the matrix, which can be described by the microdispersion TEM-images of NR-CNT (N with 20 phr CNT, t TEM-images of NR-CNT (N with 20 phr CNT, t Correlation between online conductance and microdispersion According to the published investigations [36, 37] multiwalled nanotube aggregates exist in shape of a web or entanglements of several tubes. In order to characterize the microdispersion of CNT in rubber, images of the samples taken along the mixing process were made by AFM. Figure 3a shows the AFM image of the sample taken at 3 min. It is obvious that the outer layer of the CNT agglomerates is eroded into a number of small aggregates which are surrounding the agglomerates as model-like described by the onion model for CB filled compounds [38-40]. Since the mixing time is still short, the small aggregates are not yet distributed far away from the agglomerate boundary. Some white regions without CNT aggregates can be observed in the AFM image, which isolate the conductive regions and keep the mixture still low conductive. When the mixing time increases till the BIT, the size of agglomerates decreases very fast. One of the AFM images of the mixture taken at the BIT (32 min) is presented in Figure 3b. Some small CNT agglomerates and CNT aggregates are easy to observe. The CNT aggregates have a size of about 400 nm and they are still inhomogeneous distributed. By progressed mixing time till 90 min the CNT sizes decrease and they seem to be more evenly distributed in the matrix. In Figure 4, three TEM images of the sample taken after 32 min mixing time made at different positions are shown. In these images the small aggregates of CNT with the size of about 300 nm (Fig. 4a and 4c) and 400 nm (Fig. 4b) and some unfilled rubber regions can be seen. That means that the CNT are irregularly distributed in the matrix corresponding to the results received by AFM (Fig. 3b). Some individual CNT connecting the small aggregates can be clearly observed. Due to the irregular and stochastic distribution of CNT aggregates the sample shows the maximum of the online conductance at this mixing time, corresponding to Figures 3b and 4. Figure 5 shows three TEM images of the sample taken after 90 min mixing time made at different sample regions. Even after very long mixing times under the technological conditions mentioned above CNT are still existent as aggregates. The CNT aggregates in the three images have a size of 200 nm. According to the morphological investigation the dispersion mechanism of CNT in rubber can be model-like illustrated by taking into account the online conductance (Fig. 6). At a short mixing time, larger agglomerates surrounded by small aggregates are isolated by the unfilled rubber, the online conductance is still zero. With progressing mixing time till the BIT the larger CNT agglomerates are eroded and become smaller. As a result the number of the small aggregates increases and they tend to move into the polymer volume. A conductive path is established connecting the agglomerates. Due to the high concentration of small aggregates building conductive pathways, the online conductance reaches the maximum at this point of time. With progressing mixing time, the CNT aggregate size does not change much but the particles move more and more into the polymer volume. Thus, the distance between the small aggregates becomes larger and the pathways break down, that leads to 32 min) at different regions of the sample 90 min) at different regions of the sample 6 Dispersion mechanism of CNT in rubber related to the run of the online conductance curve (schematically) the decay of the online conductance in this period. The presence of small CNT aggregates even at very long mixing times is the main reason for the low conductivity values of the nanocomposites in spite of adding 20 phr of CNT. Wetting behavior The close correlation between conductance and macrodispersion has been discussed already above (Fig. 2). Taking into consideration now additionally the rubber part in gel L, more insight into the mechanism of the mixing process of CNT can be received. Figure 7 represents the correlation between the online conductance, the macrodispersion of CNT and the rubber part in gel L. The rubber part L NR increases much earlier than conductance and dispersion. According to the discussion made by Manas-Zloczower [39, 40] and us [22] regarding the infiltration and dispersion processes, rubber generally first can infiltrate the outer layer of filler KGK Juni

5 PRÜFEN UND MESSEN TESTING AND MEASURING Online conductance, macrodispersion index and wetting behavior of CNT in rubber (N with 20 phr CNT, T A 25 C, n 50 rpm, 0.6) 8 Online conductance and modulus of elasticity versus mixing time (N with 20 phr CNT, T A 25 C, n 50 rpm, 0.6) 9 Normalized online conductance (a) and macrodispersion index (b) in dependence on mixing time for different initial chamber temperatures (N with 20 phr CNT, n 50 rpm, 0.6) aggregates after wetting its surface. This filler layer is then eroded and a new surface is available. The new surface is progressively wetted again by rubber molecules. Therefore, in the case of CB wetting and dispersion takes place simultaneously. However, it was found that CNT with NR show another behavior than CB with NR. Obviously, the NR molecules are able to wet the surface of the CNT aggregates very quickly, and they infiltrate into the aggregates also very fast without causing a dispersion of the aggregate in the beginning of this process. From this behavior follows, that the rubber content in the rubber-filler gel L, characterizing especially the wetting process, increases very fast already after a short mixing time as visible in Figure 7. Only after a given mixing time the dispersion process starts with a delay. Simultaneously with the begin of the dispersion process the online conductance increases. Mechanical properties The discussion of the correlation between the macrodispersion determined by the online conductance and the mechanical properties has to be restricted to the short period of the mixing process between the t onset and the BIT because of the possible degradation of the rubber matrix at longer mixing time. As shown in Figure 8, in the period between t onset and BIT there is a direct correlation between the online conductance and the E-modulus. As discussed above, in this period the strongest changes of the agglomerate sizes are observed. At a short mixing time large unfilled rubber regions are still available which determine mainly the mechanical properties of the composite having the lower value of the modulus of elasticity. With increasing mixing time the rubber volume becomes filled by the CNT aggregates, and as expected the modulus of elasticity increases. Effect of technological parameters on the online conductance As shown in Figure 2, the BIT is the mixing time when the slope of the macrodispersion index curve turns to become degressive and the online conductance curve reaches the local maximum value. Thus the BIT can be used as a criterion for the estimation of the influence of the technological parameters on the CNT dispersion. For the discussion of the effect of the technological parameters on the conductivity the online conductance curve was normalized with respect to the conductance value determined at the BIT. The normalized conductance curves of CNT filled natural rubber N for the initial chamber temperatures 25 C and 50 C are presented in Figure 9a. At the higher temperature the shear forces during the mixing process are reduced due to the decrease of the polymer matrix viscosity. That slows down the dispersion of CNT and hence the online conductance curve shifts to longer mixing times. In Figure 9b, the CNT macrodispersion index received for different initial chamber temperatures is presented versus the mixing time. The CNT macrodispersion index increases in the same manner like the corresponding normalized conductance curves (Fig. 9a). The influence of shear rate was investigated by the use of different rotor speeds of 90, 330 KGK Juni 2009

6 0 a) b) 0 Normalized conductance in dependence on mixing time as function of rotor speed (N with 20 phr CNT, T A 50 C, 0.6) Normalized conductance in dependence on mixing time and viscosity (a) as well as polarity (b) of the matrix (NR with 20 phr CNT, T A 25 C, n 50 rpm, 0.6) 2 3 a) b) 2 Online conductance versus mixing time for SBR and NR single compounds and their 50/50 SBR/NR blend with 20 phr CNT (T A 50 C, n 90 rpm, 0.5) 3 Wetting behavior of SBR and NR single rubbers (a) as well as their 50/50 SBR/NR blend and blend phases (b) 50 and 30 rpm (Fig. 0). The normalized conductance shows a strong dependence on the rotor speed. When the rotor speed increases, the onset time t onset and the BIT obviously shift to shorter mixing times. At higher rotor speed the higher shear forces accelerate the CNT dispersion which leads to the earlier appearance of the conductivity signal. Effect of material parameters on the online conductance The effect of the viscosity on the online conductance curve was investigated by use of the different natural rubbers N0, N and N2. The normalized conductance versus mixing time for these compounds is presented in Figure a. The unmasticated N0 shows the BIT at 52 min. With a moderate mastication (N) the BIT shifts to 32 min. This is related to optimal interaction between infiltration speed of rubber chains into CNT aggregates and the shear stress transfered by the mechanical forces of the mixing aggregate to the interface between polymer and filler agglomerates. Such an optimum is necessary, to start the dispersion mechanisms running at the filler agglomerates. When the rubber is masticated too strong (N2), the BIT shifts to the much higher value of about 90 min, because the viscosity of the rubber becomes low and the shear forces are too small for an effective dispersion of the filler agglomerates. Furthermore, also the effect of polarity of the polymer matrix was characterized by investigation of CNT-polymer compounds on the basis of the masticated natural rubber N2 and epoxidized natural rubber ENR- 25 and ENR-50 (Fig. b). As shown in Table 2, these three rubbers have nearly a similar viscosity. In the compounding process they also show nearly the same development of torque and mass temperature in dependence on mixing time. But due to the presence of epoxy groups in the ENR, both polar rubbers ENR-25 and ENR-50 show a stronger interaction with CNT than the nonpolar natural rubber N2. N2 shows the longest BIT. The BIT shifts to shorter times, when the amount of epoxy groups increases to 25 mole % and 50 mole %, respectively. The shift of the BIT to a shorter mixing time due to the increase of rubber polarity is different to the results described for CB filled rubber compounds in our previous work [23]. Dispersion and distribution of CNT in SBR/NR blends In heterogeneous SBR/NR blends, the viscosity and polarity ratio of SBR and NR can essentially influence the dispersion and the phase specific distribution of CNT. In order to characterize the dispersion and distribution of CNT in the rubber blend, 20 phr of CNT was added into a 50/50 SBR/NR blend. Figure 2 shows the online conductance of the compounds on the basis of NR, SBR and their 50/50 blend in dependence on the mixing time. Compared to NR (N) SBR shows a very long BIT that indicates the more slow dispersion of CNT in SBR in comparison to N. The BIT of the SBR/NR blend is located between the BITs of the single rubber compounds. It is worth to note that the value of the online conductance of the blend at the BIT is lower than that of the single rubber compounds. According to our previous findings on CB filled rubber [30], the conductance curve of the blend depends on the morphology of the polymer phases (isle-matrix or co-continuous) and on the local filler distribution in the blend phases. If the filler is distributed evenly in the blend phases, then the online conductance curve KGK Juni

7 PRÜFEN UND MESSEN TESTING AND MEASURING 4 should lie directly between the curves of the blend components. Otherwise, if CNT is localized preferentially in one of the blend phases, and this phase will form islands in the other phase (matrix) with lower CNT content, a lower value of the online conductance of the blend system is expected, because the conductance of the matrix with the reduced CNT content is dominant for the conductivity measurement. Thus, the position of the conductance curve of the blend in Figure 2 is related to an uneven distribution of CNT in the blend. To quantify and discuss the distribution kinetics of CNT in the blend phases the wetting behavior of the blend and its components was investigated. In Figure 3a the wetting behavior of the single SBR and NR rubbers to CNT is presented. SBR and NR wet CNT with different rates and after a certain time the rubber part in gel L reaches a plateau when no free CNT surface is available anymore. SBR wets the surface of CNT more slowly than NR because the bulky styrene groups restrict its mobility and infiltration into the filler aggregates. In Figure 3b the wetting behavior of the 50/50 SBR/NR blend is shown. The curve of the blend lies between the curves of single NR and SBR. Using the TGA method [30] for the evaluation of filler distribution the contribution of the blend components L B(SBR) and L B(NR) is determined from L B(SBR/NR). In the first stage L B(SBR) and L B(NR) increase up to 5 min, after that L B(NR) decreases while L B(SBR) increases steadily. That relates to the fact that the slight polar SBR chains replaced the non-polar NR chains on the surface of CNT. The kinetics of CNT distribution in the blend was characterized using the procedure described in [30] and presented in Figure 4. The amount of free CNT being not yet wetted by any rubber decreases sharply and 4 Kinetics of CNT distribution in 50/50 SBR/NR blend after 5 min mixing time no free CNT is available anymore. At the same time the amount of CNT distributed in the SBR and NR phase increases fast. However, more CNT is distributed in NR than in SBR because of the faster wetting rate of NR compared to SBR. After 5 min mixing the amount of CNT in NR starts to decrease while the amount of CNT in SBR continuously increases. Since after 5 min mixing time no free CNT is available, the increase of CNT in SBR is attributed to the CNT transfer process from the NR phase to the SBR phase as a result of the replacement of NR on the CNT surface by SBR. Conclusions Carbon nanotubes (CNT) are of high interest as a new nanofiller in polymer materials. For the optimization of the composite properties, an effective dispersion and distribution of CNT in the polymer matrix is necessary. The present work had shown that the method of the online measured electrical conductance can be used successfully as a tool for the analysis of the dispersion and distribution of CNT in rubber during the melt mixing process. The conductance-time curves of CNT-rubber compounds show basically the same course like the conductance-time curves of carbon black filled rubber compounds during the mixing process in the internal mixer. Like in the case of CB filled rubber composites also for CNT filled rubber compounds a strong correlation between the online conductance, the macrodispersion and mechanical properties was found. Both technological and material parameters influence the online conductance curves of the CNT-rubber systems. Viscosity and polarity of the matrix polymers affect the dispersion behavior of the CNT agglomerates in a strong manner. The analysis of the CNT-rubber gel is a significant tool for the analysis of the wetting behavior of the polymer to the CNT. By means of the TGA method the local distribution of CNT in the blend phases of a binary SBR/NR blend was quantified. Acknowledgement The authors wish to thank the German Research Foundation (DFG) for the financial support of this work. We thank Bayer Materials Science for providing CNT and Dr. Godehardt and Mrs. Becker (Martin Luther University Halle-Wittenberg, Department of Physics) for the TEM-images. The authors Dr.-Ing. Hai Hong Le and Dr.-Ing. Sybill Ilisch are co-worker in the Polymer Technology group of Prof. Dr.-Ing. habil. Hans-Joachim Radusch in the Center of Engineering Sciences of the Martin Luther University Halle- Wittenberg. Gaurav Kasaliwal was there student of Applied Polymer Technology. References [] J. A. Fagan, B. Landi, I. Mandelbaum, J. R. Simpson, V. Bajpai, B. J. Bauer, J-Phys-Chem. B0 (2006) [2] A. Rasheed, M. Dadmun, I. Ivanov, P. F. Britt, D. B. Geohegan, Chem. Mater. 8 (2006) 353. [3] Z. Jia, Z. Wang, C. Xu, J. Liang, B. Wei, D. Wu, S. Zhu, Mater. Sci. 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