Dispersion of carbon black

Satisfactory dispersion of the carbon black is essential to the production of rubber compounds possessing the maximum possible resistance to wear, tensile strength and abrasion resistance. The methods used to measure/estimate the degree of dispersion are reviewed in this paper.Most current methods are based on some form of microscopy. Light microscopy (at small magnifications) of cryomicrotomed rubber specimens in transmitted light is used to some extent. However, the preparation of the specimen is too time-consuming to warrant the use of the method for routine inspection. This has led to the development of an instrument—the Dispergator—which employs split field microscopy of freshly-cut samples to reduce the total time of testing (including the time required for specimen preparation) to about 1 min.     

Dispersion of multiwalled carbon nanotubes in a rubber matrix using an internal mixer: Effects on rheological and electrical properties

The dispersion of multiwalled carbon nanotubes (CNTs) in an ethylene propylene rubber matrix was investigated using an internal mixer. Poly(ethylene‐co‐polyvinyl acetate) (EVA) statistic copolymer was used as a dispersing agent. The effects of the concentration of the dispersing agent and the matrix viscosity on the quality of the dispersion of 1 wt % of CNTs were studied by using microscopy and rheology in the melt state. It was demonstrated that the dispersion is governed principally by the viscosity of the matrix. As expected, better dispersion was observed when the matrix exhibited a lower viscosity. The influence of the filler content on the rheological and electrical properties is presented. A Cross model with a yield stress is proposed to describe the rheological behavior of these materials, which exhibit a viscoelastic solid behavior from 1 wt % CNT content. Electrical measurement data indicate that the electrical percolation threshold was 2.9 wt %. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1597–1604, 2011     

Dispersion and phase separation of carbon nanotubes in ultrathin polymer films

The inner structure and nanoscale distribution of the stiffness was studied for polymer-single-wall carbon nanotube composites. Dispersion of nanotubes in a polystyrene and polyurethane polymer matrix was achieved by a proper choice of the organic solvent (NMP) and sonification of polymer/SWNT solutions. Ultrathin nanocomposite films were prepared through a dip-coating procedure and possessed a noticeable degree of nanotube orientation in the direction of the applied shear force. Peculiarities of the phase separation in the films were studied by atomic force microscopy (with application of force modulation mode to map the nanotube distribution within the polymer matrix) and Raman spectroscopy.     

Mechanical and rheological properties of poly(ethylene-co-ethyl acrylate) as a function of carbon black content

Carbon black (CB) filled poly(ethylene-co-ethyl acrylate) (EEA-CB) is used as conductive phase in conductive polymer composites (CPC). Electrical conductivity of CPC obtained from blends of immiscible polymers results from CB particles localization within the material, which depends on composition and processing conditions. It is particularly important to control viscosity of such systems as this parameter determines both the phase morphology and conductive pathway structure. The small scale, at which CB particle aggregation/dispersion phenomena occur within CPC, makes direct observations difficult. But the effect of carbon black particles/polymers interactions is clearly visible by means of rheological measurements. A strong reinforcing effect of CB on CPC in both solid and liquid states has been noticed. This phenomenon has been analyzed using classical models as a function of temperature and CB content. The results confirm the necessity of CPC rheology control especially during the process to achieve good reproducibility of electrical properties.     

Electrical properties of carbon black in an SBR–wax matrix

The resistivity and dielectric constant for carbon black (5–12 vol-%) in a nonconducting matrix have been measured over the range 20–90°C and dc to 2–10⁵ Hz. Styrene–butadiene rubber dissolved in tetracosane (22 parts SBR to about 70 parts wax) constituted the matrix. Wide variations in resistivity and dielectric constant with temperature and/or frequency were observed. A theory is presented to explain the experimental observations. It correctly predicts the qualitative features of the experimental results but its predictions are not quantitatively accurate.     

Characterizing elemental, equivalent black, and refractory black carbon aerosol particles: a review of techniques, their limitations and uncertainties

Elemental-, equivalent black- and refractory black-carbon are terms that have been defined in order to dissect the more general term, black carbon, into its component parts related to its specific chemical and optical properties and its impact on climate and health. Recent publications have attempted to clarify the meaning of these terms with respect to their environmental impact, particularly on climate. Here, we focus on the measurement aspects, reviewing the most commonly implemented techniques for the direct and indirect derivation of black carbon properties, their strengths, limitations, and uncertainties, and provide a non-exhaustive bibliography where the reader can find more detailed information. This review paper is designed as a guide for those wishing to learn about the current state of black carbon measurement instrumentation, how calibration is carried out, when one instrument may have the advantage over another, and where new techniques are needed to fill important knowledge gaps.     

Dispersion stabilities and rheological properties of fumed silica suspensions

Herein, we have reviewed fumed silica suspensions in dispersing fluids, polymer melts, and polymer solutions, focusing on their dispersion stability and rheological properties as a function of the surface character of fumed silica powders and the silica volume fraction, ?. Hydrophilic fumed silica powders are well dispersed at ? < 0.01 in polar dispersing fluids or polar polymer melts, and their phase states change from sol to gel with increasing ?. Such changes should also be strongly related to the rheological responses of the hydrophilic fumed silica suspensions, which change from Newtonian flow behavior to gel-like elasticity with increasing ?. On the other hand, hydrophobic fumed silica powders are stabilized in both polar and nonpolar dispersing fluids, depending on the interactions between the surface hydrophobic moieties and the dispersing fluids, in addition to those between the residual surface silanol groups and dispersing fluid, except for the particle–particle interactions. Moreover, the effects of the adsorption and desorption of polymers, as well as of non-adsorbing polymers on the dispersion stability and rheological behavior of fumed silica suspensions are discussed, by taking account of their optical microscopic observation and SANS curves.     

Electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer as a function of vinyl acetate content

The electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer was measured as a function of carbon and vinyl acetate (VAc) content. For the composites whose matrices contain less than 32 wt% ofVAc content, a sharp break point of the relation between carbon content and conductivity was observed. The conductivity jumps as much as ten orders of magnitude at the break point. The critical carbon content corresponding to the break point can essentially be predicted by our previous model. This model was derived under certain assumptions, the most important of which is that when the interfacial excess energy introduced by carbon particles into the polymer matrix reaches a universal value,g ^*, the carbon particles begin to coagulate so as to avoid any further increase of energy and to form networks which facilitate electrical conduction. On the other hand, for the composites whose matrices contain more than 32 wt% ofVAc content, a sharp break of the relation between the carbon content and conductivity cannot be observed and conductivity increases continuously with increasingVAc content. In this region ofVAc content, carbon particles were dispersed well in theVAc rich matrices. This is because the presence of polar groups in aVAc component enhances its bonding to conductive fillers. In this case, the interfacial excess energy,g, seems to be the caseg0. Better dispersibility of fillers in this region ofVAc content can be shown from an electron micrograph (TEM).     

Electrical properties and conductive mechanisms of immiscible polypropylene/Novolac blends filled with carbon black

Carbon black (CB)-filled immisicible thermoplastic/thermosetting polymer blends consisting of polypropylene (PP) and Novolac resin were reported in this paper. The PP/Novolac/CB blends with varied compositions and different processing sequences were prepared by melt-mixing method. The CB distribution, conductive mechanism and the relationship between morphology and electrical properties of the PP/Novolac/CB blends were investigated. Scanning electron microscopy (SEM), optical microscopy and extraction experiment results showed that in PP/Novolac blends CB particles preferentially localized in the Novolac phase, indicating CB has a good affinity with Novolac resin. The incorporation of CB changed the spherical particles of the dispersed Novolac phase into elongated structure. With increasing Novolac content, the elongation deformation of Novolac phase became more obvious and eventually the blends developed into co-continuous structure, which form double percolation and decrease the percolation threshold. When CB was initially blended with PP and followed by the addition of Novolac resin, the partial migration of CB from PP to the Novolac phase was possibly occurred. The addition of Novolac to PP evidently increases the storage modulus G′, loss modulus G″ and complex viscosity η^∗. The addition of CB to PP/Novolac blends further increase η^∗, and it increases with increasing CB loading, which was related to the change of composite morphology.     

Electrical conductivity and phase transition studies of some selected Congo red-metal complexes

The electrical properties of Congo Red dye (L) and its metal (M) complexes ofML molar ratios of 11 and 21, whereM=Cr(III), Fe(lII), Cu(II), Zn(II), Zr(IV), Th(IV) and UO₂(II), indicated semiconducting behaviour. The activation energies and electrical conductivities depend on the ionic charge of the metal chelates. The activation energies of 11 metal complexes are greater than those of 21 metal complexes. The conductivity data obtained are interpreted on the basis of the molecular structure of the Congo Red complexes. One phase transition was obtained during DTA study of Congo Red dye at 212°C. This phase transition may be due to the rotation of the two naphthalene rings and the N=N groups around the diphenyl group centre.     

Evaluation of carbon black distribution in different phases of compatible blend of EVA/NBR through electrical,mechanical and morphological test

The paper reveals the influence of different methods of carbon black (CB) incorporation in the compatible blend of 50/50 (wt %) Ethylene vinyl acetate (EVA) and Acrylonitrile butadiene elastomer (NBR) on different properties of vulcanized blend compounds. The partitioning of two types of CB in two different phases of the blend was estimated from dynamic mechanical analysis (DMA). The distribution of CBs due to preferential addition in different phases of the blend affects property variations in different degrees. From the analysis of SEM, TEM, AFM and electrical property measurements, it is found that mixing method significantly affects the electrical properties, morphology, and surface topography. The variation in AC conductivity and surface resistance study confirms the formation of different conductive network of CB with variation in mixing technique and it is supported by morphology analysis. The DMA have shown that CB has higher affinity towards less viscous EVA phase. This is further corroborated by the surface energy measurement, which in turn controls the electrical conductivity behaviour as well as mechanical properties of the blends.     

Infrared studies of fluoroalcohol-base complexes in the gas phase,carbon tetrachloride solutions and argon matrices

Hydrogen bonded complexes of fluoroalcohols with oxygen-containing bases like dimethyl ether and alkanols have been investigated in argon matrices, in CCl₄ solutions and in the gas phase. The increase of the proton donor capacities with succesive substitution of fluorine atoms into the alkyl group of alcohols is indicated by a strong increase of the shift Δν of the OH stretching frequency in the complexes. For alkanols as acceptors, an increase of Δν is observed along the series CH₃OH, CH₃CH₂OH, (CH₃)₂CHOH, and (CH₃)₃CHOH. The frequency shifts Δν increase as one passes from the gas phase to CCl₄ solutions and argon matrices.     

Evidence of wormlike micellar behavior in chromonic liquid crystals: rheological, X-ray, and dielectric studies

We report rheological, X-ray, and dielectric investigations on a chromonic liquid-crystalline system formed by aqueous solutions of a food coloring agent, Sunset Yellow, in the absence and upon addition of salt. The salt-concentration dependence of the steady-state viscosity at low shear rates has a non-monotonic variation and is qualitatively similar to the behavior seen in wormlike micellar systems, a surprising result since chromonic systems are expected to be non-micellar in character. More interestingly, for a particular low concentration of the salt (20 mM), the viscosity increases by 3 orders of magnitude in comparison with that of the pure chromonic material. The dynamic (oscillatory) rheological data bring out features which can be described in terms of a microstructure formation. X-ray and dielectric studies show that certain characters of the aggregates formed by the Sunset Yellow molecules are not altered by the addition of salt.     

Adsorption of benzene on graphitized thermal carbon black: reduction of the quadrupole moment in the adsorbed phase

The performance of intermolecular potential models on the adsorption of benzene on graphitized thermal carbon black at various temperatures is investigated. Two models contain only dispersive sites, whereas the other two models account explicitly for the dispersive and electrostatic sites. Using numerous data in the literature on benzene adsorption on graphitized thermal carbon black at various temperatures, we have found that the effect of surface mediation on interaction between adsorbed benzene molecules must be accounted for to describe correctly the adsorption isotherm as well as the isosteric heat. Among the two models with partial charges tested, the WSKS model of Wick et al. that has only six dispersive sites and three discrete partial charges is better than the very expensive all-atom model of Jorgensen and Severance. Adsorbed benzene molecules on graphitized thermal carbon black have a complex orientation with respect to distance from the surface and also with respect to loading. At low loadings, they adopt the parallel configuration relative to the graphene surface, whereas at higher loadings (still less than monolayer coverage) some molecules adopt a slant orientation to maximize the fluid-fluid interaction. For loadings in the multilayer region, the orientation of molecules in the first layer is influenced by the presence of molecules in the second layer. The data that are used in this article come from the work of Isirikyan and Kiselev, Pierotti and Smallwood, Pierce and Ewing, Belyakova, Kiselev, and Kovaleva, and Carrott et al.     

A rheological and morphological study of a copolyester liquid crystal/polypropylene blend system

The effects of composition and shear rate on the rheology and morphology of blends of LC–3000, a thermotropic liquid crystalline polymer consisting of 60/40 of hydroxybenzoic acid and poly(ethylene terephthalate), with polypropylene were studied. It was found that the rheological properties depend in a complex manner on composition and applied shear. Both positive and negative deviations from the log-additivity rule were observed at low shear rates. Significant viscosity reduction was measured when the dispersed phase was a nematic TLCP. The accompanying microstructural transitions were characterized a posteriori, and it was found that the state of dispersion of the TLCP phase also influences the viscosity reduction phenomenon. A nematic, fibrillar TLCP phase shows a viscosity reduction of the order of fourfold with respect to the viscosity of the matrix. Another important finding was that the stability of these fibers would not be expected from work on other non-TLCP-containing immiscible blends. This suggests that the unique rheology of the TLCP minor phase is relevant to the formation of stable fibers. © 1996 John Wiley & Sons, Inc.     

Self-sustaining hybrid electrode prepared from polyaniline,carbon nanotubes,and carbon fibers: morphological,structural, and electrochemical analyses

The self-sustaining hybrid electrode was prepared via chemical polymerization of aniline in acid medium containing dispersed carbon nanotubes (CNT), using carbon fiber (CF) as conducting substrate. The ternary composites called PAni/CNT/CF were characterized in order to evaluate their morphologies, structures, and thermal properties. The influence of the polyaniline (PAni) layer in the ternary composite properties was studied considering different deposition times on CF samples (30, 60, and 90 min). The ternary composite morphologies were observed by scanning electron microscopy while thermal structural analyses were obtained using thermogravimetric measurements. The structural features were analyzed by Raman scattering spectroscopy and Fourier transform infrared spectroscopy (FTIR). The possible interactions between PAni and CNT were discussed on the basis of Raman and FTIR spectra. These spectroscopic analyses also confirmed that the PAni present in the composite is in the emeraldine (ES) salt form. Furthermore, the ternary composites were also evaluated by electrochemical measurements such as cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) techniques. The results showed good charge storage capacity for ternary composites, in particular, for PAni/CNT/CF obtained with 90 min of deposition time, which exhibited specific capacitance of around 500 F g^?1. Therefore, this electrode was selected to build a prototype of type I supercapacitor. This device presented specific capacitance of around 143 F g^?1 after 3200 charge/discharge cycles.