Carbon Black Aggregates Research Articles

Microwave properties of natural rubber based composites comprising conductive carbon black/silica hybrid fillers

Hybrid fillers have been prepared by impregnation of conductive carbon black with different amounts of silicasol, equivalent to 3 % and 7 % silica, respectively. The fillers have been characterized and their effect upon the microwave properties of natural rubber based composites has been also investigated. The results obtained show that, the silica (dielectric) phase is distributed both over the surface and inside the carbon black aggregates (conductive phase). Thus, the interaction between the particles of the conductive filler (building of conductive pathways) is restricted. It has been established that the microwave properties studied are dependent on the ratio between the filler’s phases. The composites filled with the hybrid filler comprising the highest amount of silica possess the best total shielding effectiveness and absorptive shielding effectiveness. In all cases absorption is the mechanism prevailing in effectiveness. Thus, the fillers obtained allow an easy control and tailoring of the elastomer based electromagnetic interference shielding materials. The investigations carried out reveal the good potential of the composites studied for finding applications as antennas, automobiles, sensors and military-related applications.

New Insights on Li4Ti5O12 Electrode/Electrolyte Interfaces: A X-Ray Photoelectron Spectroscopy and Scanning Auger Microscopy Stud

Spinel Li4Ti5O12 (LTO) is considered as a good alternative negative electrode material for Li-ion batteries [1], due to its negligible change of lattice parameter during insertion/extraction of lithium ions [2], resulting in a very low capacity decrease upon cycling. However, the reactivity of LTO toward commons carbonates based electrolytes has been evidenced by surface analysis [3] and an important gassing occuring at the electrode/electrolyte interface was reported [4]. Therefore it is essential to better understand the interfacial phenomenons. This work aims to achieve a precise understanding of the LTO electrode/electrolyte interfaces in relation with batteries electrochemical performances. The influence of various parameters (cycling temperature, electrode and electrolyte composition, cycling potential window) upon the solid electrolyte interphase (SEI) formation and dissolution through the first cycle was systematically investigated. The evolution of those interfaces after long cycling is currently being studied. Finally, Li4Ti5O12/LiMn2O4 cells having potential assets in term of cost and safety [5], will be investigated, in order to point out the changes in the SEI formation due to interactions between the two electrodes. The samples are analysed by X-ray Photoelectron Spectroscopy (XPS) and Scanning Auger Microscopy (SAM), two complementary extreme surface characterization techniques (analysis depth 5-10 nm), operating at different spatial resolutions. The galvanostatic curves obtained for the Li4Ti5O12/Li half-cells first cycle at room temperature and at 85°C are presented on figure 1. The number of electrons exchanged per unit formula (Li4Ti5O12) at the end of the first discharge increases with the temperature indicating that more electrons are exchanged at higher temperatures to reach the same state of charge. The irreversible capacity also increases with the temperature at the first cycle. Those electrochemical results are directly correlated with the increase of the SEI thickness with the temperature, as observed by XPS and SAM experiments at the end of the first discharge. Indeed at room temperature, the two components doublets in the titanium spectrum (figure 2a) indicate a partial reduction of titanium ions consecutive to lithium insertion. The component at low binding energy in oxygen spectrum (figure 2b) is characteristic of oxygen ions in the LTO material, while the ones at higher binding energy reveal the presence of deposited species at the electrode surface. In addition to the components characteristic of PVdF binder and carbon black (CB) constituents of the electrode, carbon spectrum (figure 2c) presents components characteristic of C-O, O-C=O and CO3 chemical environments, confirming the formation of a SEI resulting from the degradation of electrolyte species. By contrast, at 85°C titanium and the component attributed to oxygen anions from the LTO lattice are not detected (figure 2c and 2d), meaning that the SEI is thicker than the XPS depth of analysis. The intensity decrease of the carbon black component (figure 2f) together with the intensity increase of C-O component, compared to room temperature, is consistent with an increase of the SEI thickness. The morphology of the electrode surface have been characterized by SEM (Figure 3a and 3c) and allow to identify LTO particles in light grey and carbon black aggregates in dark grey, for both temperatures. In contrast, the carbon elemental SAM mappings at room temperature (figure 3b) displays a higher carbon concentration on top of carbon black aggregates, whereas the mapping at 85°C (figure 3d) evidences a more homogeneous carbon distribution on top of the electrode, indicating a complete covering of the electrode surface by the SEI species. [1] J. B. Goodenough, Journal of the American Chemical Society 135 (4) (2013) 1167–1176. [2] K. Zaghib, Journal of Power Sources 196 (8) (2011) 3949–3954. [3] L. El Ouatani, Journal of The Electrochemical Society 156 (6) (2009) A468. [4] Y.-B. He, Scientific Reports 2. [5] I. Belharouak, Journal of the Electrochemical Society 159, A1165–A1170 (2012). Figure 1

A TEM study of morphological and structural degradation phenomena in LiFePO4-CB cathodes

LiFePO4-based cathodes suffer from various degradation mechanisms which influences the battery performance. In this paper morphological and structural degradation phenomena in laboratory cathodes made of LiFePO4 (LFP) mixed with carbon black (CB) in an 1 mol L-1 LiPF6 in EC:DMC (1:1 by weight) electrolyte are investigated by transmission electron microscopy (TEM) at various preparation, assembling, storage and cycling stages. High-resolution TEM (HRTEM) imaging shows that continuous SEI layers are formed on the LFP particles and that both storage and cycling affects the formation. Additionally loss of CB crystallinity, CB aggregation and agglomeration is observed. Charge-discharge curves and impedance spectra measured during cycling confirm that these degradation mechanisms reduce the cathode conductivity and capacity.

A review: role of interfacial adhesion between carbon blacks and elastomeric materials

Abstract Carbon blacks (CBs) have been widely used as reinforcing materials in advanced rubber composites. The mechanical properties of CB-reinforced rubber composites are mostly controlled by the extent of interfacial adhesion between the CBs and the rubber. Surface treatments are generally performed on CBs to introduce chemical functional groups on its surface. In this study, we review the effects of various surface treatment methods for CBs. In addition, the preparation and properties of CB-reinforced rubber composites are discussed. Key words: rubber, carbon blacks, surface treatments, interfacial adhesion 1. Introduction Rubber exhibits superior viscoelastic properties and improves the lifespan of products which continue to be transformed. At first, natural rubber (NR), which is composed of isoprene monomers, was obtained from nature. Later, as industries developed, synthetic rubbers were produced to supplement the production of NR. In particular, studies have been conducted on a new kind of rubber that is made of butadiene, namely, a copolymer of acrylonitrile butadiene rubber (NBR) and styrene butadiene rubber (SBR) as shown in Fig. 1 [1-6].However, rubber lacks sufficient physical strength, which makes it unsuitable for various applications. For this reason, fillers, such as carbon materials and silica, are added to rubber to form rubber composites with improved mechanical behaviors [7-27].In recent years, carbon materials have been widely used as reinforcing agents in high-per -formance composite materials [28-35], adsorbents [36], electrochemistry [37], and energy storage materials [38]. Among various carbon materials used as reinforcing agents, carbon blacks (CBs) are the oldest carbon derivatives produced by the incomplete combustion of petroleum products, such as fluid catalytic cracking tar and coal tar. Moreover, the particle size, structure, and surface conditions of CBs (Fig. 2) make them popular reinforcing agents [19-21].CBs contain more than 95% amorphous carbon, and their particle sizes vary from 5 to 500 nm. The physical properties of CBs vary with the production method and the raw materials used, which makes them suitable for applications in various fields. The mixing ratio of CBs in automobile tires is 50%, while that in other rubber products is approximately 30%. Rela-tively large amounts of reinforced CBs should be added to NR to attain acceptable mechani-cal properties. Cohesion occurs between CB particles due to chemical and physical bonds. The chemical composition of CB aggregates is 90%–99% carbon, 0.1%–1.0% hydrogen, 0.2%–2.0% oxygen, and a small amount of sulfur and ash. In addition, oxygen-containing functional groups, such as the carboxyl, hydroxyl, and quinine groups, exist on the surfaces of CBs. These are called surface functional groups. These surface functional groups increase the chemical and physical bonding between the CBs particles and the rubber matrix [39-43]. Therefore, the addition of CBs to rubber results in the formation of composites with im-

New Insights on Li4Ti5O12 Electrode/Electrolyte Interfaces: A X-Ray Photoelectron Spectroscopy and Scanning Auger Microscopy Study

Spinel Li4Ti5O12 (LTO) is considered as a good alternative negative electrode material for Li-ion batteries [1], due to its negligible change of lattice parameter during insertion/extraction of lithium ions [2], resulting in a very low capacity decrease upon cycling. However, the reactivity of LTO toward commons carbonates based electrolytes has been evidenced by surface analysis [3] and an important gassing occuring at the electrode/electrolyte interface was reported [4]. Therefore it is essential to better understand the interfacial phenomenons. This work aims to achieve a precise understanding of the LTO electrode/electrolyte interfaces in relation with batteries electrochemical performances. The influence of various parameters (cycling temperature, electrode and electrolyte composition, cycling potential window) upon the solid electrolyte interphase (SEI) formation and dissolution through the first cycle was systematically investigated. The evolution of those interfaces after long cycling is currently being studied. Finally, Li4Ti5O12/LiMn2O4cells having potential assets in term of cost and safety [5], will be investigated, in order to point out the changes in the SEI formation due to interactions between the two electrodes. The samples are analysed by X-ray Photoelectron Spectroscopy (XPS) and Scanning Auger Microscopy (SAM), two complementary extreme surface characterization techniques (analysis depth 5-10 nm), operating at different spatial resolutions. The galvanostatic curves obtained for the Li4Ti5O12/Li half-cells first cycle at room temperature and at 85°C are presented on figure 1. The number of electrons exchanged per unit formula (Li4Ti5O12) at the end of the first discharge increases with the temperature indicating that more electrons are exchanged at higher temperatures to reach the same state of charge. The irreversible capacity also increases with the temperature at the first cycle. Those electrochemical results are directly correlated with the increase of the SEI thickness with the temperature, as observed by XPS and SAM experiments at the end of the first discharge. Indeed at room temperature, the two components doublets in the titanium spectrum (figure 2a) indicate a partial reduction of titanium ions consecutive to lithium insertion. The component at low binding energy in oxygen spectrum (figure 2b) is characteristic of oxygen ions in the LTO material, while the ones at higher binding energy reveal the presence of deposited species at the electrode surface. In addition to the components characteristic of PVdF binder and carbon black (CB) constituents of the electrode, carbon spectrum (figure 2c) presents components characteristic of C-O, O-C=O and CO3 chemical environments, confirming the formation of a SEI resulting from the degradation of electrolyte species. By contrast, at 85°C titanium and the component attributed to oxygen anions from the LTO lattice are not detected (figure 2c and 2d), meaning that the SEI is thicker than the XPS depth of analysis. The intensity decrease of the carbon black component (figure 2f) together with the intensity increase of C-O component, compared to room temperature, is consistent with an increase of the SEI thickness. The morphology of the electrode surface have been characterized by SEM (Figure 3a and 3c) and allow to identify LTO particles in light grey and carbon black aggregates in dark grey, for both temperatures. In contrast, the carbon elemental SAM mappings at room temperature (figure 3b) displays a higher carbon concentration on top of carbon black aggregates, whereas the mapping at 85°C (figure 3d) evidences a more homogeneous carbon distribution on top of the electrode, indicating a complete covering of the electrode surface by the SEI species. [1] J. B. Goodenough, Journal of the American Chemical Society 135 (4) (2013) 1167–1176. [2] K. Zaghib, Journal of Power Sources 196 (8) (2011) 3949–3954. [3] L. El Ouatani, Journal of The Electrochemical Society 156 (6) (2009) A468. [4] Y.-B. He, Scientific Reports 2. [5] I. Belharouak, Journal of the Electrochemical Society 159, A1165–A1170 (2012). Figure 1

Study on the dispersion of carbon black/silica in SBR/BR composites and its properties by adding epoxidized natural rubber as a compatilizer

This paper studied the influence on the properties of SBR/BR composites filled with carbon black (CB) and silica via adding epoxidized natural rubber (ENR‐25) as a compatilizer. Payne effect, morphology, crosslink density, mechanical, and dynamic properties were studied. The results showed Payne effect receded by adding ENR‐25 to SBR/BR/CB/silica composites and the aggregation of CB and silica both weakened as well. Thus, tear strength and modulus were improved significantly, also the crosslink density and bond rubber content Dynamic Mechanical Analyzer (DMA) data indicated the tanδ value at 0°C and 60°C increased when CB was replaced by silica. Meanwhile, the value at 0°C exhibited a greater improvement than that at 60°C when adding ENR‐25, which means an excellent wet traction performance. The abrasion loss and aging resistance presented well with ENR‐25 as a compatilizer, but no improvement on the heat build‐up performance. POLYM. COMPOS., 39:377–385, 2018. © 2016 Society of Plastics Engineers

Use of Classification Trees and Rule-Based Methods to Predict Shapes of Nano-Aggregates of Reinforcement Fillers

While manufacturing composite materials, reinforcement fillers inevitable collide with each other and subsequently they congregate to aggregates with different shapes. The shape of these nanoparticles aggregates are of great significance for the mechanical material properties and in consequence, knowing the percentage of aggregates of each shape within of a specific group of shapes can give an idea of the final properties of the material. This work classifies aggregates, a new dataset of 5713 carbon black aggregates gathered based on transmission electron microscopy image processing, using several classification trees and rule-based methods. Based on these methods several models are built, trained and tested to perform the classification. And then, the most reliable and accurate model to classify aggregates is selected, obtaining a testing accuracy of the 74.57% according to their shape.

Characterization of hybrid fillers based on carbon black of different types obtained by impregnation

The paper presents the investigations on obtaining dual phase fillers with preset silica content running a successful impregnation of two completely different types of conventional carbon black with silicasol. The hybrid fillers studied were characterized by atomic absorption spectroscopy and inductively coupled plasma–optical emission spectroscopy. The total pore volume, the average pore diameter, the specific surface area, the oil absorption number, and iodine adsorption of the fillers were also investigated. The distribution of both phases within the hybrid filler obtained and their interpenetration were investigated with scanning transmission electron microscopy-energy dispersive X-ray spectroscopy. The hybrid products obtained were investigated as reinforcing fillers of natural rubber-based composites. The results obtained show that the suggested impregnation with silicasol of conventional carbon black is a perspective method for preparation of carbon-silica dual phase fillers. The method provides an easy control over the quantitative ratio between the two phases. The fillers thus prepared do not change significantly the curing and mechanical characteristics of the vulcanizates, but improve their thermal aging resistance. The isolation of the carbon black aggregates by the silica phase, and the interpenetration of the two phases is a prerequisite to obtain elastomer composites of good mechanical and microwave properties suitable for producing of microwave shielding devices.

Quantifying the Influence of Carbon Black De-Agglomeration on the Electrochemical Performance of Lithium-Ion Battery

Lithium ion batteries for PHEV`s, HEV`s and EV`s have to meet different requirements like high energy density, high power density and always low production costs at high durability. As wide-spread standard, electrodes for lithium ion batteries are produced by mixing and dispersing active materials with conductive additives, binder and solvent. This process step strongly influences the electrode’s electrochemical performance in the subsequently produced battery cell. Thus, high quality mixing, de-agglomeration and dispersing of all solid components in the solvent has to be ensured to produce high performance electrodes. One important aspect in the dispersing process is the de-agglomeration of carbon black. Modifying the agglomerate size and shape of carbon black has a strong influence on electrochemical performance due to structural changes of electrode properties like electrode porosity and conductivity. For this reason, our work focuses on experiments regarding the changes in electrochemical performance due to different de-agglomeration degrees of carbon black processed with a continuously operated twin-screw extruder, suitable for large scale production of suspensions with NCM and artificial graphite as active material. Suspensions with differently de-agglomerated carbon black were produced by varying the tensile stress acting inside the suspension and the residence time through changes in the tip speed of extruder screws and volumetric flow rate of solids and solvent (N-methyl-pyrrolidone) at constant solids content in the suspension. In order to examine the influence of the carbon black agglomerate sizes on electrochemical performance, a specific preparation of the suspension samples became necessary: The carbon black is separated from coarser active material particles via centrifugation and stabilized with a suitable stabilizer, which was used to preserve the sizes of the carbon black agglomerates and to prevent reagglomeration in the diluted suspension required for particle size analysis. In the next step, the agglomerate size of different suspensions was identified via laser diffraction analysis using a Horiba LA-960 Laser Particle Size Analyzer with two light sources, a laser diode with 650 nm and a light emitting diode (LED) with 405 nm wavelength. The analysis displayed a strong bimodal distribution with a shifting peak in the single-digit µm-range representing carbon black agglomerates and a stationary peak at a few hundred nanometers representing smaller carbon black aggregates. A pilot-scale coater with a combined reverse-roll comma bar system and a dryer length of 6 meters was used to produce electrodes continuously out of selected suspensions. Afterwards, structural properties of electrodes produced out of differently stressed suspensions were analyzed using mercury porosimetry and electrode conductivity analysis. Mercury porosimetry was used to visualize changes in the pore structure of electrodes, especially in a range of 0.1 to 4 µm pore diameter. In this pore size range the varying agglomerate sizes have a great impact on the electrode´s pore structure due to carbon black agglomerates acting as spacers between active material particles. Changing the size of carbon black agglomerates also significantly influences the properties of the carbon black conductive network resulting in modified electrode conductivity: A finer distribution and better de-agglomeration of carbon black lead to higher electrode conductivity which is beneficial to some degree for the electrochemical performance at higher c-rates, especially regarding the cathode. The effect of structural changes on the electrochemical performance of electrodes was examined performing c-rate-tests up to 5 C in half and full cells. The influence of these changes in electrode properties became apparent especially at higher c-rates, where limiting effects in ionic and electrode conductivity, influenced by electrode porosity and conductivity, become more important. Good electrochemical performance only is attainable with suitable electrode porosity and well-developed conductivity network of carbon black. Summing up all experimental results we are able to relate process parameters and structure properties of the electrodes and link these structural changes with the resulting electrochemical performance. Significant differences in electrochemical performance were traceable to structural changes in the electrodes, which necessitate distinct process know-how in the dispersing step. This process-structure-property-relationship leads to a deeper understanding for the continuously operating industrial process of extrusion and for the optimized production of electrodes for lithium ion batteries. Figure 1

Theoretical Analysis of Relationship Between Porous Electrode Structure and Mass Transfer Performance for PEFCs By Direct Measurement and Simulation

In order to reduce the cost of polymer electrolyte fuel cell system, it is important to increase current density. However, the limiting current density cannot be expanded because it depends on the oxygen transfer performance from gas channels to electrode catalyst surfaces. Therefore, it is important to reduce the oxygen diffusion resistance of the porous electrode components, which are composed of gas diffusion layer (GDL), micro-porous layer (MPL) and catalyst layer (CL). In this study, the oxygen diffusion resistances of these porous media were directly measured and calculated by three-dimensional porous structure reconstructed by X-ray CT and FIB-SEM, and the relationship between heterogeneous structure and the mass transport performance was examined. Figure 1 shows the example of reconstructed image. The porous structure of GDL was obtained by X-ray CT under compression. The porous structures of MPL and CL were obtained by FIB-SEM with different carbon-PTFE weight ratio and different ionomer-carbon weight ratio, respectively. And the validity of 3D structure, which was obtained after image processing, has been confirmed by pore size distribution and porosity. Effective oxygen diffusion coefficient of each porous electrode was experimentally measured by O2-N2 inter-diffusion resistance method [1]. In addition, the effect of Knudsen diffusion can be separated from overall diffusion resistance by the dependency of full pressure. Furthermore, the effective diffusion coefficient with or without Knudsen effect could be obtained by tortuosity and pore size calculated in porous structure shown in Fig.1 [2]. Figure 2 shows the relationship between porosity and relative diffusion coefficient of each component and model structures (vertical orientation, sphere packing, fibrous structure). In the case of GDL and MPL, experimental values are almost equal to calculation results from reconstructed structure. In the case of CL, these experimental and calculated results are almost same. However, although the value of MPL agreed with that of model structure of particle packing, the relative diffusion coefficients of MPL and CL, which has the same carbon black particles, were different from each other. It is conceivable that the difference is caused by the effect of ionomer distribution. In order to compare the effect of ionomer coating distribution, simulated catalyst layer was numerically made by packing carbon black aggregate and modeling ionomer heterogeneous coating[3], and it was confirmed that the ionomer coating distribution affected the oxygen diffusion performance in catalyst layer. Acknowledgement This work is a part of the project, Strategic Development of PEFC Technologies for Practical Application, by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Effect of curing on activation energy and dielectric properties of carbon black–epoxy composites at different temperatures

The effect of curing on activation energy and dielectric properties of carbon black–epoxy (CB–EP) composites has been reported at different temperatures and frequencies. The activation energy was found to be higher for the room temperature cured CB–EP samples as compared with the thermally cured CB–EP samples. Curing behavior of epoxy nanocomposites prove that epoxide molecules contribute to the curing reaction and reacted with them to form a cross-linked network. Dielectric constants of thermally cured CB–EP samples were higher than the room temperature cured samples. The results showed that activation energy, decreased with an increase in the concentration of carbon black in the composite, which may be due to an increase of polarization energy and/or charge carrier density leading to a decrease of the domain boundary potential of carbon black aggregates into the epoxy matrix. At room temperature, the electrical conductivity is due to electron tunneling and hopping. Dielectric constant of the CB–EP composite increase with increase in temperature and decreases with an increase in frequency from 0.5kHz to 10kHz for both room temperature cured and thermally cured specimens. The peak height of the dielectric constant curve of both cured samples decreases with increasing frequency.

The effect of MWCNTs on the electrical properties of a stretchable carbon composite electrode

Abstract Stretchable electrodes are of great interest with increasing demands for flexible electronic devices. Carbon black polymer composites do not show increasing resistivity during stretching, but resistivity decreases in a certain range. However, the electrical conductivity of carbon black is insufficient for electrodes. Multi-wall carbon nanotubes (MWCNTs) are carbon-based nanostructures that impart good electrical conductivity and flexibility with a high aspect ratio. CNTs may help to improve the electrical conductivity of carbon black. In this study, MWCNTs were added to a carbon black electrode with a simple process and then investigated. Adding MWCNTs introduced two benefits to the electrical properties of carbon black composites for use as a stretchable electrode. The addition of MWCNTs reduced the electrical resistivity of the carbon electrode as it connected non-contacting carbon black particles to enhance the effective conductive network. Also, MWCNTs minimized the increase in the resistance of the carbon electrode during stretching because they bridged separate carbon black aggregates and aligned along the stretching direction to enhance conductive path and inhibit crack growth. Additionally, the electrical resistance of MWCNTs in the carbon black electrode was maintained after repetitive stretching. A stretchable electrode showed stable electrical behavior under a strain of 25% after repetitive stretching.

Effect of the carbon black content on the thermal, rheological and mechanical properties of thermoplastic polyurethanes

Different mixtures of thermoplastic polyurethane (PU) with different amounts of nanometric carbon black (CB) were prepared by mechanical stirring in organic solvent, and their thermal, rheological, viscoelastic and mechanical properties were investigated. The rheology of the PU–CB mixtures in methyl ethyl ketone was optimized, allowing good dispersion of the CB in the polyurethane matrix once the solvent was removed; an increase in the number and size of carbon black aggregates in the polyurethane matrix was obtained by increasing the carbon black loading. Addition of carbon black improved the rheological and viscoelastic properties of the polyurethane, and the larger was the carbon black content, the higher was the storage modulus and the lower was the tanδ value. Moreover, the addition of higher amounts of CB changed the viscoelastic behaviour of the polyurethane, which became mainly elastic over all temperature range. On the other hand, the addition of CB loadings up to 12 wt% increased the thermal stability of the polyurethanes and increased the elongation-at-break without noticeable reduction in the tensile strength.

A conductive foam: Based on novel poly(styrene‐b‐butadiene‐co‐styrene‐b‐styrene) tri‐block copolymer filled by carbon black

ABSTRACTIn this article, a conductive foam based on a novel styrene‐based thermoplastic elastomer called poly(styrene‐b‐butadiene‐co‐styrene‐b‐styrene) tri‐block copolymer S(BS)S was prepared and introduced. S(BS)S was particularly designed for chemical foaming with uniform fine cells, which overcame the shortcomings of traditional poly(styrene‐b‐butadiene‐b‐styrene) tri‐block copolymer (SBS). The preparation of conductive foams filled by the carbon black was studied. After the detail investigation of cross‐linking and foaming behaviors using moving die rheometer, the optimal foaming temperature was determined at 180°C with a complex accelerator for foaming agent. Scanning electron microscopy (SEM) images shown that the cell bubbles of conductive foam were around 30–50 µm. The conductivity of foams was tested using a megger and a semiconductor performance tester. SEM images also indicated that the conductivity of foams was mainly affected by the distribution of carbon black in the cell walls. The formation of the network of the carbon black aggregates had a contribution to perfect conductive paths. It also found that the conductivity of foams declined obviously with the foaming agent content increasing. The more foaming agent led to a sharp increasing of the number of cells (from 2.93 × 106 to 6.20 × 107 cells/cm3) and a rapid thinning of the cell walls (from 45.3 to 1.4 µm), resulting in an effective conductive path of the carbon black no forming. The conductive soft foams with the density of 0.48–0.09 g/cm3 and the volume resistivity of 3.1 × 103−2.5 × 105 Ω cm can be easily prepared in this study. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41644.

Effect of Water Sorption on the Electronic Conductivity of Porous Polymer Electrolyte Membrane Fuel Cell Catalyst Layers

A method is described for measuring the effective electronic conductivity of porous fuel cell catalyst layers (CLs) as a function of relative humidity (RH). Four formulations of CLs with different carbon black (CB) contents and ionomer equivalent weights (EWs) were tested. The van der Pauw method was used to measure the sheet resistance (RS), which increased with RH for all samples. The increase was attributed to ionomer swelling upon water uptake, which affects the connectivity of CB aggregates. Greater increases in RS were observed for samples with lower EW, which uptake more water on a mass basis per mass ionomer. Transient RS measurements were taken during absorption and desorption, and the resistance kinetics were fit using a double exponential decay model. No hysteresis was observed, and the absorption and desorption kinetics were virtually symmetric. Thickness measurements were attempted at different RHs, but no discernible changes were observed. This finding led to the conclusion that the conducting Pt/C volume fraction does not change with RH, which suggests that effective medium theory models that depend on volume fraction alone cannot explain the reduction in conductivity with RH. The merits of percolation-based models were discussed. Optical micrographs revealed an extensive network of "mud cracks" in some samples. The influence of water sorption on CL conductivity is primarily explained by ionomer swelling, and its effects on the quantity and quality of interaggregate contacts were discussed.

Interfacial tension and surface elasticity of carbon black (CB) covered oil-water interface.

Carboxyl-terminated carbon black (CB) particles have been proposed as readily available, biocompatible dispersants to stabilize oil-in-water emulsions after an oil spill. Since the reduction in interfacial tension and the increase in interfacial elasticity are the key parameters which relate interfacial mechanics to emulsion stability, this investigation explores the effect of CB adsorption and surface coverage on oil-water interfacial tension and elasticity. Flocculation of CB was explored as ionic strength was increased from 0 to 0.6 M, approximately the salinity of seawater. As salinity increases, CB aggregates into larger particles from 100 nm to 6 μm. The interfacial tension and dilational viscoelasticity were measured for two systems: a drop of a CB suspension in oil and an inverted oil drop in a CB suspension. For the arrangement of a CB suspension drop in oil, most of the CB settles and accumulates toward the bottom of the drop with only small surface adsorption and no appreciable effect is observed on the dynamic interfacial tension or the dilational viscoelasticity. On reversing the arrangement to an inverted oil drop in CB suspension and increasing the convection of the outer phase, the surface coverage increases considerably. The CB coverage becomes more uniform with higher convection with an average value of approximately 2.6 g/m(2), which is representative of the coverage in Pickering emulsions stabilized by CB particles. The CB coverage decreases the surface tension from about 30 to 8.5 mN/m accompanied by an increase in the surface elasticity to 20.7 mN/m. The sharp contrast between the results from the CB suspension drop and the oil drop could be partially due to the effect of the wetting characteristics of the particles or due to the significant differences between the convection in the two cases.

STUDIES ON BOUND RUBBER OF CB BEFORE/AFTER VULCANIZATION OF ISOPRENE RUBBER

ABSTRACT The high abrasion furnace (HAF), fast extrusion furnace (FEF), and fine thermal (FT) loadings used in this study were adjusted to keep the carbon black (CB)–specific area of cetyl trimethyl ammonium bromide adsorption to 2490 m2g−1. Their polyisoprene (IR) compounds and vulcanizates were investigated. Regarding the dependence of the CB gel fraction (FCB gel) on the IR gel/CB weight ratio (WRIR/CB), the amount of CB in the CB gel increased with a larger CB aggregate size, whereas the amount of the IR gel decreased. With regard to the dependence of the activation energy (ΔE(T2)) of the spin–spin relaxation time (T2) on the CB aggregate size, an immobilized rubber layer around CB formed more easily in the order of FT < FEF < HAF. Moreover, it became clear from the relationship between WRIR/CB and ΔE(T2) that the amount of the IR gel in the CB gel increased with decreasing ΔE(T2). The unique ratio of the surface area to the volume of CB aggregates (SCB/VCB) was obtained from results of three-dimensional transmission electron microscopy observation. The dependence of the amount of dibutyl phthalate (DBP) adsorption and compressed DBP adsorption on SCB/VCB was approximately linear, which suggested that SCB/VCB was closely related to CB aggregates and CB agglomerates. The linear relationship seen between SCB/VCB and ΔE(T2) revealed that an immobilized rubber layer was present around CB. The dependence of (qCB/qIR)(WRIR/CB) on SCB/VCB was also investigated using the densities (ρIR and ρCB) of IR and CB. The slope (tirl) of their approximately linear relationship was about 3.9 nm, which almost agreed with the bound rubber thickness reported in the literature to date. It is also inferred that because the intercept (α), which reflects the change in the IR gel weight fraction, was about 0.04 (4%), the IR gel weight fraction changed very little between before and after vulcanization.

Carbon black reinforced C8 ether linked bismaleimide toughened electrically conducting epoxy nanocomposites

The present work deals with the toughening of brittle epoxy matrix with C8 ether linked bismaleimide (C8 e-BMI) and then study the reinforcing effect of carbon black (CB) in enhancing the conducting properties of insulating epoxy matrix. The Fourier transform infrared spectroscopy (FTIR) and Raman analysis indicate the formation of strong covalent bonds between CB and C8 e-BMI/epoxy matrix. The X-ray diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM) analysis indicate the event of phase separation in 5wt% CB loaded epoxy C8 e-BMI nanocomposites. The impact strength increased up to 5wt% of CB loading with particle pull and crack deflection to be driving mechanism for enhancing the toughness of the nanocomposite and beyond 5wt% the impact strength started to decrease due to aggregation of CB. The dynamic mechanical analysis (DMA) also indicates the toughness of the nanocomposites was improved with 5wt% of CB loading due to the phase segregation between epoxy and C8 e-BMI in the presence of CB. The electrical conductivity was also increased with 5wt% of CB due to classical conduction by ohmic chain contact.

Control of carbon black aggregate size by using polystyrene-polyethylene oxide non ionic diblock copolymers

The fine fraction of carbon black (CB) sample N234, initially prepared by the furnace process, was obtained by sieving and it was then dispersed in aqueous medium at various aqueous phase pH. Further, adsorption from water onto this non porous CB particles, of polystyrene-polyethylene oxide (PS-PEO), non ionic diblock copolymers, having molecular weights, Mw=2000 and Mw=4000g/mol, were investigated at ambient temperature. For the bare CB particles, prepared in the absence of copolymers, the TEM micrographs show aggregates and/or agglomerates having sizes depending of the aqueous phase pH, and formed from fused primary particles having sizes in the range 13–17nm. These aggregates develop intra-porosity that result from their branching shape. The CB bare particles prepared in acidic aqueous dispersion form mostly ellipsoidal agglomerates having sizes exceeding 500nm. However, by increasing the pH of the medium from pH=3 to pH=10, and after drying the CB dispersion, aggregates shaped as “bunch” of grapes and having smaller sizes are observed by TEM. The microelectrophoresis studies of these dispersions indicate that the CB particles are positively and negatively surface charged at pH values, respectively, below and above the Isoelectrical point (IEP) which is about pH∼6. Such electrokinetic behavior of the CB aqueous dispersion results from the presence on the CB surface of acidic and basic functional groups. However, upon PS-PEO copolymers adsorption onto CB, reduction in the magnitude of zeta potential, and shift of the Isoelectrical point (IEP) to lower pH values were observed. Such IEP shift is related to the copolymer adsorption on the Stern layer and to the position of the shear plane in the electrical double layer. In addition, the copolymer adsorption was found to reduce the CB particle size achieving a minimum value in water of about 200nm, resulting in sterically stable CB aqueous dispersions.

ナノフィラー充塡架橋ゴムにおけるナノフィラーの構造と物性

Advantages of 3D-TEM/electron tomography are described for development of rubber science and technology. The first result of visualization of carbon black (CB) network is shown, which was obtained by combining 3D TEM/electron tomography and electric characteristic measurements. A novel analysis for characterization of the CB network is proposed on the basis of gelation mechanism of polymer network, where structural parameters of crosslined and branched chains of CB aggregates are determined by 3D-TEM/electron tomography and are utilized. Good relationships between the CB network structures and electrolytic properties are also shown in this review paper.