Carbon Black Dispersion Research Articles

PVB, PVAc and PS pressure sensors with interdigitated electrodes

Miniature sensors, which are rugged and reliable in nature, are essential to meet the growing demand for environmental and biomedical monitoring systems. Developing such sensors using screen-printing and drop coating techniques allows the combination of two cost effective and flexible technologies. Using this approach, a wide variety of materials could be combined to produce sensors with the desired physical properties. Silver electrodes were screen-printed onto alumina substrates, while polymer/carbon-black composites based on polyvinyl butyral, polyvinyl acetate and polystyrene were deposited by drop coating. The addition of surfactant resulted in a more even dispersion of carbon-black throughout the composites, which was observed by TEM. The frequency dependence of the composites also confirmed this result. Pressure was applied using a Lloyd Instruments LR50k in the range 0–2500 kPa and the sensitivity was taken to be the slope of the graph. It was found that the materials displayed a high sensitivity to pressure with good repeatability. Detailed studies of the composites temperature dependency showed that each material has a negative temperature coefficient and were particularly sensitive when the temperature was brought below room temperature. This was improved by coating the sample surface.

Critical Role of Polymeric Binders on the Electronic Transport Properties of Composites Electrode

The role of the polymeric binder nature and composition on the electronic transport properties of composite electrodes based on , carbon black (CB), and poly(ethylene oxide) (PEO)/poly(vinylidene difluoride)-co-hexafluoropropylene/ethylene carbonate–propylene carbonate (EC–PC)/Li bis(trifluoromethansulfon)imide binders were examined. The variation of the electrical conductivity vs CB volume fraction is typical of tunneling-percolation systems. Lower percolation threshold found for preplasticized binders is related to a more efficient CB dispersion due to the presence of EC–PC in the liquid suspension at the time of the composite processing. Above the conductivity is a unique function of the PEO to CB concentration ratio in the suspension, . This ratio controls the amount of polymer that adsorbs at the surface of the CB particles before the CB conducting network forms. The insertion behavior was studied at low current rate, for which ionic conductivity is not a limiting factor. The electrochemical capacity sharply increases at . However, for CB content typical of practical composite electrodes, the electronic conductivity of the CB network is not the only parameter that governs the electrode performance. It depends also on the electronic wiring at the interface, which is improved when adding EC–PC and lithium salt in the formulation.

Simulation method for complex permittivities of carbon black/epoxy composites at microwave frequency band

AbstractThis paper studied the permittivity of carbon black/epoxy composites at microwave frequencies. The measurements were performed for permittivity at a frequency band of 0.5–18 GHz and for DC conductivity to find the percolation threshold of composite samples of 0.0–1.5 wt % of carbon black in epoxy resin. The experimental results show that the complex permittivity of the composite depends strongly on the nature and concentration of the carbon black dispersion. The frequency spectrums of dielectric constants and AC conductivities of composites were investigated by using the descriptions found in percolation theory. A new model, that is a branch of Lichtenecker–Rother formula, is proposed to obtain a rule of mixture to describe the complex permittivity of the composite as function of frequency and concentration of carbon black. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2189–2195, 2006

Polypropylene/Nylon‐66/Carbon Black Blends Processed at Temperatures Just Below the Nylon Melting: Anisotropy in Structure and Properties

AbstractIn‐situ fibrillation of nylon (Ny) is obtained by compounding and processing its binary blends with polypropylene (PP) and ternary carbon black (CB) containing blends just below the melting temperature (Tm) of the dispersed, Ny phase, yet, above that of the PP. At such low temperatures the Ny behaves as an elastic solid deforming under the elongational flow of the molten PP matrix. Without the mediation of PP, Ny could not be processed or compounded at such low temperatures. This structured anisotropy in both binary and ternary blends resulted in anisotropy in the electrical and dielectric properties of the blends. Moreover, the dynamic electrical behavior was used as a powerful tool to study the CB dispersion mode in the polymer blends.

Effect of cationic surfactant and block copolymer on carbon black particle surface charge and size

In this paper, the size reduction and surface charge modification of carbon black particles aqueous dispersions by cationic surfactant, cetyltrimethylammonium chloride (CTAC), and amphiphilic polymer, polystyrene-polyethylene oxide (PS-PEO) are described. Aqueous and vacuum dried carbon black dispersions containing various amounts of CTAC surfactant or PS-PEO copolymer were analysed by dynamic light scattering, microelectrophoresis and by transmission electron microscopy. In presence of CTAC and PS-PEO additives, the final carbon particle sizes in aqueous dispersions were in the range 170–230 nm, whereas in vacuum dried dispersions, the achieved particle sizes were in the range 327–372 nm. Blank experiments made in absence of surfactant and copolymer gave carbon black particles mean sizes of 330 and 470 nm, respectively, in aqueous and vacuum dried dispersions. Further, in presence of PS-PEO copolymer, the magnitude of zeta potential was reduced from −50 to −18 mV, whereas in presence of CTAC surfactant, the sign of zeta potential was reversed from negative to positive and its magnitude decreased from −50 to +35 mV. Beyond the size reduction and the surface charge modification of carbon particles by CTAC surfactant and PS-PEO copolymer, the preparation mode of carbon dispersions was also found to affect the carbon particle properties. The overall data are explained in term of the nature of interactions occurring at carbon-aqueous solution interface. The knowledge of such interactions is the prerequisite to prevent the aggregation of carbon particles either in solution or in polymeric matrix.

Polymer Blend for Electrolyte and Electrode Coatings

AbstractSummary: The thermal and morphological properties of PEO/copolyether electrolyte and carbon black composite have been studied. A copolyether poly(propylene glycol)‐block‐poly(ethylene glycol)‐block‐poly(propylene glycol) bis(2‐aminopropyl ether) was used at 20 wt.‐% in relation to PEO in order the improve the carbon black dispersion through interaction with the amino end capped function. The polymer matrix presented semicrystalline structure and the addition of LiClO4 and carbon black decreases significantly the crystallinity of the system. Sub‐micrometric dispersion of carbon black was observed. The conductivity results as a function of temperature exhibited a typical VTF behaviour for the electrolyte. Almost constant conductivities of 2 × 10−4 S · cm−1 were observed for the composite with 5 wt.‐% of carbon black, in the range of temperature between 35 and 95 °C, which indicates a significantly contribution of electronic conduction.

Waterborne latex coatings of color: I. Component influences on viscosity decreases

For almost two decades, it has been known that the addition of colorants to a waterborne latex coating thicknened with an associative thickener will result in a viscosity loss. The influence of surfactants on viscosity variations in waterborne latex coatings, as discussed in our most recent JCTCoatingsTech article,1 is the source of the viscosity decreases. To evaluate this problem, aqueous solutions containing large quantities of five different surfactants, and the smallest particle size of the colorants, carbon black (CB), were prepared. Large quantities of surfactant were used to allow for adsorption on, and stabilization of, CB. When traditional associative polymers (HMHEC, HASE, and a telechelic HEUR) were used to thicken carbon black dispersions, viscosity decreases were not observed, for most of the surfactnat is adsorbed on the CB’s surface. There is enough surfactant, however, to promote viscosity decreases in comb-HEUR thickened CB dispersions. Moving beyond the colorant dispersions, the CB, yellow, or red colorants were then added to a commercial latex paint that contains many surfactants, glycol ether, and coalescing aids, and significant viscosity decreases were observed. The decreases were very dramatic as the colorant concentration was increased to obtain deeper color tones, due to the additional excess surfactant added to the coating. Reduction in total surfactant levels in the colorant was an obvious solution, but this led to rub-up incompatibility. The conflict between viscosity retention and rub-up incompatibility was resolved when the surfactant concentration was reduced by adding to the colorant formulation compositionally different hydrophobically-modified poly(oxyethylenes) and hydrophobe-modified maleic acid co-oligomers.

Conductivity of polyolefins filled with high‐structure carbon black

AbstractThe electrical conductivities of various polyolefins filled with a high‐structure carbon black (CB) were studied. Typical percolation behaviors were observed in all of the materials studied. At a critical CB content, which defined the percolation threshold, CB formed conductivity pathways, and resistivity fell sharply from a value characteristic of an insulator into the range of 10–100 Ω cm. The dependence of the percolation threshold on the matrix viscosity was understood in terms of competing effects on CB dispersion during blending and CB flocculation during compression molding. For the conditions used in this study, polypropylene with a melt flow index of about 50 was optimum. Flocculation in the quiescent melt was studied directly by atomic force microscopy. Conductivity pathways formed over time by CB agglomeration. The temperature dependence of the percolation time was described by an Arrhenius relationship. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1799–1805, 2005

Nano-structural observation of carbon black dispersion in natural rubber matrix by three-dimensional transmission electron microscopy

Nano-structural observation of carbon black dispersion in natural rubber matrix by three-dimensional transmission electron microscopy

Characterization of non-aqueous dispersions of carbon black nanoparticles by electrochemical impedance spectroscopy

Understanding fundamental electrochemical characteristics of industrial fluids, lubricants and their contaminants will allow for improvements in monitoring the performance of existent, and the formulation of new advanced industrial fluids and lubricants. This study focusses on the electrochemical characterization of model systems of colloidal dispersions of carbon black (CB), validation of these models, and investigation of applications of electrochemistry for determining the relative effectiveness of dispersants. Utilizing electrochemical impedance spectroscopy (EIS) analysis of industrial colloidal dispersions, an experimental method was developed to study the mechanism of dispersant/carbon black interactions, and the role of these interactions in the formation and stabilization of colloidal dispersions. Experimental EIS parameters such as conductivity, permittivity, critical frequencies of impedance and modulus relaxations, and impedance and modulus values were used in modeling equations describing particle sizes and interaction mechanisms occurring in CB dispersions. Results from the modeling equations show that dispersant micelles averaging 9 nm in diameter were present in solution. The dispersant micelles have a tendency to aggregate and form a loose “network”. In solutions containing CB, dispersants surround CB particles and form a colloidal suspension. An increase in relative concentration of the dispersant leads to a better stability of the suspension and prevents CB agglomeration. The diameter of the suspended CB particles decreases with added dispersant until a stabilization point is reached at approximately 200 nm. The validity of the impedance data and results of the modeling equations were confirmed by other analytical techniques, such as quasi-elastic light scattering and adsorption analysis.

Adsorption of Surfactants on Carbon Black‐Water Interface

Carbon black dispersions are prepared using anionic, cationic, and nonionic surfactants as dispersants in aqueous medium and adsorption behavior of these surfactants is studied along with wettability and stability. Adsorption isotherms for all the surfactants are shown to be of Langmuir type except for lauryl dimethybenzyl ammonium chloride (BKC) where the amount adsorbed increases with increase in the concentration of BKC. Out of the two anionic surfactants used [sodium dodecyl sulphate (SDS) and sodium dodecylbenzene sulphonate (SDBS)], SDBS showed higher adsorption, wettability and stability. Among cationic surfactants viz. cetyltrimethyl ammonium bromide (CTAB), cetylpyridinium chloride (CPC), BKC and Stertile, stertile showed better adsorption. In the case of nonionic surfactants viz. nonylphenol ethoxylates (NP 20 and NP 40) and Triton X‐100, the maximum amount of surfactant adsorbed decreased in the order NP 40 < NP 20 < Triton X‐100. Stability of the dispersion improved in the same order. Addition of salt resulted in increase in both effectivenss and efficiency of the ionic surfactant adsorbing on the carbon black surface while the stability decreased. Pretreatment of carbon black surface with triethanolamine had negligible effect on the adsorption behavior of non ionic surfactants but the wettability and stability improved.

Determination of the electrical behaviour of surfactant treated polymer/carbon black composite gas sensors

The effect of surfactants on the properties of poly(vinyl acetate) (PVAc)/carbon black (CB) composite gas sensors was examined. Percolation curves of the composites with and without surfactant were prepared. The percolation curves of surfactant treated composites showed that the resistivity of the composite was increased due to better dispersion of the CB and also the prevention of the CB from reagglomerating after shear mixing. TEM images were used to investigate the effect of adding surfactant to the composites. These images confirmed that the surfactants significantly improved the level of dispersion of CB in the composites and prevented reagglomeration of the CB. The response (ΔR/R%) was increased by addition of surfactants and implies that increased dispersion increases response to methanol vapour.

Online Electrical Conductivity as a Measure to Characterize the Carbon Black Dispersion in Oil Containing Rubber Compounds with a Different Polarity of Rubber

Abstract The influence of viscosity, polarity of the rubber matrix and the types and contents of extender oil on the carbon black dispersion has been characterized using the online electrical conductivity measurement. A corresponding change of the online conductivity with the rubber infiltration and extent of carbon black dispersion has been observed. The infiltration rate increases with increasing polarity and decreasing viscosity of the rubber matrix, whereby the matrix polarity shows a stronger effect than the viscosity. The oil addition accelerates the infiltration process. This is caused by the reduction of the matrix viscosity and the intensification of the filler-matrix interaction. Oil addition affects the carbon black dispersion in non-polar rubber much more than in polar rubber. Furthermore, in non-polar rubber, polar oil shows a stronger effect than non-polar oil.

Thixotropy and rheopexy of aggregated dispersions with wetting polymer

Different types of thixotropy of aggregated dispersions of magnetic metal, nonmagnetic iron oxide and carbon black particles in organic solvents with a polymer containing pendant wetting groups are studied. Thixotropic behavior depends on the type of aggregation which determines the type of structural recovery in and after shear. Metal particles form denser aggregates combined into flocs or networks recoverable in or after shear, which results in positive thixotropy with up-shear stress-vs-shear-rate curves running above down-shear curves. By contrast, iron oxide and carbon black particles form looser aggregates which re-flocculate slower in shear and do not re-flocculate at all at rest after shear, which results in rheopexy with recovery strongly accelerated by shear and negatively thixotropic loops. Viscoelastic moduli of the latter systems are determined by their shear history, e.g., G′ decreases with the preceding shear rate and does not recover. The effect of the wetting polymer on time-dependant phenomena is twofold: It suppresses thixotropy by consolidating aggregates, but slows down recovery, so that rheopexy is maximized at certain polymer-to-pigment ratios. Furthermore, two types of rheopexy are discriminated. Recovery rate of carbon black dispersions is controlled by the current shear rate only, resulting in thixotropic loops strongly dependent on sweep time. On the other hand, recovery rate of iron oxide dispersions has a long memory of shear history, which leads to thixotropic loops almost insensitive to sweep time. The difference is attributed to slow shear-induced dilation/shrinkage of aggregates built from elongated iron oxide particles, as opposed to stable aggregates of carbon black.

Carbon Black Dispersion Measurement in Rubber Vulcanizates via Interferometric Microscopy

Abstract A new method for characterizing the carbon black dispersion in rubber compounds is introduced. This technique is based on interferometric microscopy (IFM) and utilizes the interference fringes between in-phase light beams reflected from the rubber sample and a smooth reference surface to measure the three-dimensional surface topography. The peaks and valleys present on the fresh-cut surface are representative of the carbon black agglomerates and are used to characterize the dispersion. A series of samples with different base rubbers and varying dispersion levels were created and characterized by both light microscopy and IFM. These results were used to generate a universal dispersion index based on the IFM data that correlates well with the LM dispersion index values. In addition, three-dimensional peak statistics were obtained from the IFM data and used to provide additional information about the carbon black agglomerate distribution. This data can be used for a more complete understanding of the compound behavior as a function of the carbon black dispersion and agglomerate distribution.

Online Characterization of the Effect of Mixing Parameters on Carbon Black Dispersion in Rubber Compounds Using Electrical Conductivity

Abstract The influences of mixing parameters on the carbon black dispersion can be characterized using the electrical conductivity online measured from internal mixer. As a measure for monitoring the development of carbon black dispersion, a normalized conductivity with regard to the conductivity measured at the BIT (black incorporation time) has been suggested. It is observed that in spite of different mixing parameters, the mixtures possessing the same normalized conductivity factor K/KBIT deliver the same carbon black dispersion and the same mechanical properties. Based on normalized conductivity, a deeper insight into the mixing kinetics can be provided to find an optimal mixing regime.

Rheology of aqueous carbon black dispersions

The interaction of carbon black with an acrylic resin has been investigated by rheology. Two carbon blacks, with similar particle size and surface characteristics but quite different particle morphologies, have been examined. These are somewhat arbitrarily denoted as “spherical” and “fractal” as shown by small-angle neutron scattering (SANS) and ultrasonic spectroscopy studies. In the absence of polymer, stable aqueous dispersions could not be obtained. Stable dispersions could be obtained, however, upon addition of polymer to a level corresponding to a ratio of 50 mg of polymer per 13 m 2 (±1 m 2) of surface area (i.e., 15 wt% particles). These stable dispersions exhibit flow typical of concentrated dispersions—Newtonian behavior up to some apparent “yield” or critical value, above which pronounced shear thinning is observed. The critical stress increases with increasing polymer concentration. When a significant amount of nonadsorbed polymer is also present, a second Newtonian plateau is superimposed on the shear-thinning behavior. This feature is observed for both particle types but is more pronounced for the fractal particle. When there is little or no nonadsorbed polymer, the viscosity of the fractal particle dispersions is greater than the viscosity of the spherical particle dispersions. At low polymer concentrations, the dispersions are predominantly viscous at low shear stresses. The phase angle decreases significantly over a narrow shear stress range and the rheology tends to more elastic behavior. At higher shear stresses, the dependence on particle morphology is weak.

Carbon black dispersions and carbon–silver combinations as thermal pastes that surpass commercial silver and ceramic pastes in providing high thermal contact conductance

Carbon black dispersions are superior to the best commercial silver and ceramic particle thermal pastes for providing high thermal contact conductance across mating surfaces that are smooth (0.05 μm). For mating surfaces that are rough (15 μm), the combined use of carbon black and silver is more effective than carbon, silver or ceramic pastes. The use of a silver paste to even out the rough surfaces prior to using the carbon black dispersion is more effective than the use of a carbon–silver mixture. For both smooth and rough surfaces, the carbon–silver mixture is superior to silver pastes. The highest conductance attained for rough surfaces is lower than that attained for smooth surfaces.

高分子のパーコレーション・フラクタル解析 ゴムコンパウンドの微細構造とフラクタル

This research is concerned with exploration of the utility of fractal for characterizing the mixing treatment applied to a rubber compound and also for characterising the filler dispersion developed during mixing. Fractal is also used for characterization of the fracture surfaces generated during tensile testing of vulcanized samples. For these purposes, Maximum Entropy Method and Box Counting Method are applied to analyze the mixing treatment and the filler dispersion, respectively. These methods are effectively used and it is found that fractal dimensions of mixer-power-traces and fracture surfaces of vulcanized rubber decrease with the evolution of mixing time while the fractal dimension of the state-of-mix also decreases. The relationship of the fractal dimensions thus determined with conventional properties such as tensile strength, electrical resistance, and fracture surfaces are then explored.Finally, the utility of the fractal methods for establishing mixing-microstructure-property relationships is compared with more conventional and well established methods such as electrical resistance and carbon black dispersion. It is found that the characterization by the fractal agrees with the conclusions from these conventional methods. In addition, it becomes possible to interpret the relationships between these conventional methods with the help of the fractal concept.

A method to control the dispersion of carbon black in an immiscible polymer blend

AbstractThe dispersion of carbon black (CB) in an immiscible polymer blend of poly‐(methyl methacrylate) (PMMA) and polypropylene (PP) was studied as the viscosity of PMMA increased. It was found that the dispersion of carbon black was strongly influenced by the viscosity of PMMA. The CB was dispersed in the PMMA phase when the viscosities of PMMA and PP are comparable, as predicted by Sumita's model. As the viscosity of PMMA increases, the CB was found to be located at the interface between the PMMA and PP phases. On further increase in the viscosity of PMMA, the CB was found to be dispersed in the PP phase. In addition, the CB dispersion in the PP/PMMA blends can significantly influence the positive temperature coefficient (PTC) intensity of the blends.