Rheological and Electrical Properties of the Suspensions of Differently Oxidized Carbon Blacks in Polar and Apolar Dielectric Dispersion Media

The results of the investigation of the rheological characteristics and electrical resistance of the suspensions of carbon black with various degrees of oxidation in apolar vaseline oil and polar castor oil are reported. It is established that, regardless of the degree of oxidation, the strength of the structure-forming bonds between aggregates of carbon black in vaseline oil is higher than that in castor oil.     

Rheological and Electrical Properties of Oxidized Carbon Black Suspensions in Vaseline Oil under Shear and Vibration

The results of investigations of the rheological characteristics and electrical resistance of the suspensions of carbon black in vaseline oil under the effects of shear and vibration were presented. The investigations are carried out on an original unit that allowed one to simultaneously subject the suspensions to shear deformation and orthogonal vibration. The electrical resistance was also measured in an ac pulsed low-voltage mode. Possible mechanisms of the suspension conductivity were considered depending on the regime of dynamic action.     

Electrical Method for Estimating the Kinetics of Suspension Structurization

The methodology of the study of the recovery kinetics of the structure of a dispersion of carbon black in vaseline oil, based on measuring the electrical resistance and capacity in an ac regime, is described.     

Kinetics of Absorption of Carbon Dioxide and Sulfur Dioxide in Fluorine-Containing Media

Kinetics and Catalysis - It has been established that the reactions of sulfur dioxide oxidation and carbon dioxide conversion take place in aqueous suspensions of calcium fluoride at room...     

The effect of oxidation on physicochemical properties and aqueous stabilization of multiwalled carbon nanotubes: comparison of multiple analysis methods

Surface oxidation can alter physicochemical properties of multiwalled carbon nanotubes (MWCNTs) and influence their aqueous stabilization. Many techniques have been used to characterize the physicochemical properties and aqueous stabilization of MWCNTs. However, the relationship between the change in physicochemical property and the aqueous stabilization of MWCNTs merits more studies, and the multiple characterization techniques have not been well compared. This study systematically and comparatively investigated the effect of oxidation on the physicochemical properties and aqueous stabilization of MWCNTs using multiple analysis methods. Increased surface area, disclosed tube ends, defects on the sidewalls, disruption of the electronic structure, and removal of metal catalysts and amorphous carbon were observed for the oxidized MWCNTs (o-MWCNTs) using the multipoint Brunauer-Emmett-Teller (BET) method, transmission electron microscope observation, Raman spectroscopy, UV-Vis spectroscopy, and thermogravimetric analysis. An oxidation-time-dependent increase in oxygen content of the MWCNTs was verified by the methods of elemental analysis, mass difference calculation, and X-ray photoelectron spectroscopy (XPS). Fourier transform infrared spectroscopy, XPS, and the Boehm titration were employed to study the functionalities on the MWCNT surfaces. Despite the limitations of these techniques, the results indicated that the dramatic increase in carboxyl groups was mainly responsible for the significant increase in oxygen content after the oxidation. The dissociation of the grafted functional groups increased electronegativity of the o-MWCNTs and facilitated the aqueous stabilization of o-MWCNTs through electrostatic repulsions. The oxidation affected the UV-Vis absorbance of MWCNT suspensions. The absorbances at 800 nm of the stabilized MWCNT suspensions had a good correlation with the MWCNT concentrations and could be used to quantify the MWCNT suspensions. The findings of this work are expected to boost the research on carbon nanotubes and their environmental behaviors.     

A new method for preparing dimethylamino-B-difluoroborine

Summary We have worked out a new method for preparing dimethylamino-B-difluoroborine by splitting hydrogen fluoride from dimethylamino-B-trifluoroborine by heating with aluminum powder in a medium of vaseline oil.     

Electrochemical oxidation of catecholamines and catechols at carbon nanotube electrodes

The differences in the electrochemical oxidation of two commonly known catecholamines, dopamine and norepinephrine, and one catechol, dihydroxyphenylacetic acid (DOPAC), at three different types of carbon based electrodes comprising conventionally polished glassy carbon (GC), nitrogen-doped carbon nanotubes (N-CNTs), and non-doped CNTs were assessed. Raman microscopy and X-ray photoelectron spectroscopy (XPS) were employed to evaluate structural and compositional properties. Raman measurements indicate that N-CNT electrodes have ca. 2.4 times more edge plane sites over non-doped CNTs. XPS data show no evidence of oxygen functionalities at the surface of either CNT type. N-CNTs possess 4.0 at. % nitrogen as pyridinic, pyrrolic, and quaternary nitrogen functionalities that result in positively charged carbon surfaces in neutral and acidic solutions. The electrochemical behavior of the various carbon electrodes were investigated by cyclic voltammetry conducted in pH 5.8 acetate buffer. Semiintegral analysis of the voltammograms reveals a significant adsorptive character of dopamine and norepinephrine oxidation at N-CNT electrodes. Larger peak splittings, DeltaE(p), for the cyclic voltammograms of both catecholamines and a smaller DeltaE(p) for the cyclic voltammogram for DOPAC at N-CNT electrodes suggest that electrostatic interactions hinder oxidation of cationic dopamine and norepinephrine, but facilitate anionic DOPAC oxidation. These observations were supported by titrimetry of solid suspensions to determine the pH of point of zero charge (pH(pzc)) and estimate the number of basic sites for both CNT varieties. This study demonstrates that carbon purity, the presence of exposed edge plane sites, surface charge, and basicity of CNTs are important factors for influencing adsorption and enhancing the electrochemical oxidation of catecholamines and catechols.     

Synthesis and electrorheological characterization of emulsion-polymerized dodecylbenzenesulfonic acid doped polyaniline-based suspensions

The electrorheological (ER) properties of dodecylbenzenesulfonic acid (DBSA) doped polyaniline suspensions in silicone oil were investigated. In contrast to chemically polymerized polyaniline in an acidic aqueous medium by oxidation polymerization, we adopted an emulsion polymerization technique in which aniline is polymerized in an emulsion of water and a nonpolar (or weakly polar) organic solvent. The effects of electric field strength and particle concentration on the ER properties of DBSA-doped polyaniline suspensions in silicone oil were then examined. Rheological measurements were also carried out using a rotational rheometer with a high-voltage generator in both controlled shear rate and shear stress modes, and the results showed that the ER properties were enhanced by increasing the particle concentration and electric field. Received: 23 August 1999 Accepted: 6 April 2000     

New view on the oxidation mechanisms of crude oil through combined thermal analysis methods

In the previous study, the oxidation behavior of four Chinese crude oils (Oil 1 to 4) in the presence and absence of rock cuttings was investigated by thermogravimetry/derivative thermogravimetry (TG/DTG) techniques and oxidation tube experiments. The present work investigates the thermal behavior of these oils by combining DTG–DTA method. First, we conducted comparative analysis about mass loss rate from DTG curves and endothermic/exothermic phenomenon from DTA curves attempting to clarify the endothermic or exothermic mechanism in crude oil low-temperature oxidation. Finally, we combined the thermal analysis method with low-temperature oil oxidation tube experiment in porous media to ascertain, whether the two methods are consistent in the aspect of low-temperature oxidation mechanism of crude oil by O₂ consumption rate and CO₂ generating rate (carbon bond stripping reaction rate). Results show that crude oils undergo an endothermic oxidation behavior during low-temperature oxidation stage, suggesting the decomposition of hydrocarbon components. Clay can play a catalytic effect on low-temperature oil oxidation. The results of DTG–DTA tests can also better reflect oil oxidation mechanism under real conditions.     

Lecithin Organogels in a Hydrocarbon Oil

We demonstrated the existence of lecithin organogel at 20°C in a system containing the following components: phospholipid mixture with 40 wt % of phosphatidylcholine, hydrocarbon (vaseline) oil, and water, at phosphatidylcholine concentrations above 1.2 wt % and in the range of W = [H₂O]/[lec] values varying from 3.25 to 7.0. The dependences of the viscosity of lecithin organogels in a hydrocarbon oil on water and lecithin concentrations, as well as on temperature were established.     

Effects of Surface Properties on Rheological and Interfacial Properties of Pickering Emulsions Prepared by Fumed Silica Suspensions Pre-Adsorbed Poly(N-Isopropylacrylamide)

The hydrophobic fumed silica suspensions physically pre-adsorbed poly(N-isopropylacrylamide) (PNIPAM) in water could prepare oil dispersed in water (O/W) Pickering emulsion by mixing of silicone oil. The resulting Pickering emulsions were characterized by the measurements of volume factions of emulsified silicone oil, adsorbed amounts of the silica suspensions, oil droplet size, and some rheological responses, such as stress-strain sweep curve and dynamic viscoelastic moduli as a function of the added amount of PNIPAM. Moreover, their characteristics were compared with those of the O/W Pickering emulsions prepared by the hydrophilic fumed silica suspensions pre-adsorbed PNIPAM. For the emulsions prepared by the hydrophobic silica suspensions, an increase in the added amount of PNIPAM led to (1) a decrease in the volume fraction of the emulsified oil in the emulsified phase, (2) both the size of oil droplets and the adsorbed amount of the corresponding silica suspensions being almost constant, except for the higher added amounts, and (3) both the storage modulus (G′) and the yield shear strain being constant. The term of 1 is the same for the emulsions prepared by the hydrophilic silica suspensions, whereas both the adsorbed amount of the corresponding silica suspension and the G′ value increase and both the droplet size and the yield shear strain decrease with an increase in the added amount of PNIPAM. The differences between the rheological properties of the emulsions prepared by the hydrophilic silica suspensions and those by the hydrophobic ones are attributed to the hydrophobic interactions of the flocculated silica particles in the Pickering emulsions.     

Leveling of reactivity for intramolecular radical substitution reactions in viscous media

A leveling of the reactivity was found for intramolecular radical reactions in substituted 2-oxyphenoxyls in viscous media. A comparison of rate constants in toluene, hexane, pentane, and vaseline oil shows that fast reactions are decelerated more rapidly than slow reactions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 334–336, February, 1994.     

不同松香改性树脂对农药可分散油悬浮剂物理稳定性的影响

研究了添加松香及其改性氢化松香甘油酯、氢化松香季戊四醇酯、松香改性对特辛基苯酚树脂对以油酸甲酯为介质的12.5%氰霜唑·吡唑醚菌酯可分散油悬浮剂物理稳定性及流变特性的影响。傅里叶变换红外光谱表征结果表明,与松香酸相比,氢化松香甘油酯、氢化松香季戊四醇酯和松香改性对特辛基苯酚树脂的羧基吸收峰消失且出现酯基的特征吸收峰。实验中,随加成烷基醇碳链的延长,软化点升高。且随着树脂的质量分数增加,制剂的粘度提高,物理稳定性也相应提高(析油率降低)。流变结果表明,添加松香改性树脂的可分散油悬浮剂体系呈正触变性,且树脂种类对体系的屈服值影响较大,具体表现为:松香改性对特辛基苯酚>氢化松香季戊四醇酯>氢化松香甘油酯>松香,制剂的物理稳定性也呈现相同的趋势。因此,松香改性树脂具有作为可分散油悬浮剂物理稳定剂的应用潜力。     

The catalytic and photocatalytic properties of InP-CdS and ZnTe-CdS system components

Catalytic and photocatalytic studies of binary and multicomponent semiconductors in the InP-CdS and ZnTe-CdS systems were performed for the examples of the oxidation of carbon(II) oxide and water and ethanol decomposition, respectively. The conditions of the most effective catalytic transformation of carbon monoxide were estimated from the results of a study of the adsorption of its participants over a wide temperature range, and the activity of catalysts was estimated from the ratio between the rate constants for the catalytic and noncatalytic reactions. Conclusions about the occurrence of photocatalytic decomposition were drawn from changes in pH of suspensions and the results of chromatographic analyses for hydrogen. Among the components of the InP-CdS and ZnTe-CdS systems, cadmium sulfide has the lowest catalytic activity (in the oxidation of CO) and the highest photocatalytic activity (in the photodecomposition of C₂H₅OH). Recommendations on the use of cadmium sulfide as an effective catalyst for the production of nontraditional fuel, hydrogen, are given.     

Assessment of surfactant adsorption in oil-based magnetic colloids

We describe in this paper different and complementary experimental methods for assessing the adsorption of surfactants on metal particles in oil-based suspensions. Two different kinds of particles are dispersed in mineral oil: iron microparticles and CoNi nanoparticles. The adsorption of oleic acid in the Fe/oil interface in diluted suspensions can be determined by obtaining the adsorption isotherm. In addition, we present a method based on the time evolution of the optical absorbance of suspensions, from which the existence of adsorption can be inferred. For concentrated suspensions, the used of optical methods is not recommended, since they are affected by a significant inaccuracy. We present here a useful alternative based on electromagnetic induction phenomena. The results obtained allow a more comprehensive knowledge of the aggregation process in concentrated suspensions. With the same purpose, a third group of experiments, based on rheological techniques, is carried out in Fe/oil and CoNi/oil concentrated suspensions. In these series of experiments, the effect of three surfactants (oleic acid, aluminum stearate and lecithin) is tested by measuring either the viscosity, or the magnetic field-induced yield stress of the suspensions. The combination of these series of experiments gives us valuable information about the most appropriate surfactant/carrier combination capable of imparting a high stability and a strong magnetorheological response in magnetic colloids.     

Characterization of silicone oil emulsions stabilized by TiO2 suspensions pre-adsorbed SDS

To study the effects of pre-adsorbed emulsifier on Pickering emulsion stability, the preparation of silicone oil emulsions by TiO₂ suspensions pre-adsorbed sodium dodecyl sulfate (SDS) at the fixed TiO₂ concentration of 0.15 g was carried out below a fiftieth of critical micelle concentration (cmc) of SDS, where all added amounts of SDS are adsorbed on the TiO₂ particles. The stability of the Pickering emulsions incorporating TiO₂ suspensions pre-adsorbed SDS was investigated by measuring the volume fraction of emulsified silicone oil, adsorbed amounts of TiO₂ suspensions pre-adsorbed SDS, oil droplet size, and some rheological responses such as the stress-strain sweep curve and strain and frequency dependences of dynamic viscoelastic moduli. The silicone oil was almost emulsified by TiO₂ suspensions pre-adsorbed SDS above cmc/10³. Increasing in the adsorbed amount of SDS on the TiO₂ particles leads to an increase in the adsorbed amounts of TiO₂ suspensions pre-adsorbed SDS. Such silicone oil emulsions for the first time showed two yield stresses in the stress-strain sweep curve as well as the oscillatory stress-strain curve. The respective yield stresses also increase with an increase in the adsorbed amounts of TiO₂ suspensions pre-adsorbed SDS. From such characteristic rheological properties and a partial sedimentation of some TiO₂ particles remained in the dispersion medium, we proposed the formation of a three dimensional network of the flocculated TiO₂ particles pre-adsorbed SDS on the silicone oil droplets.     

Linear Viscoelastic Behavior of Multiphase Dispersions

The linear viscoelastic behavior of polymer-thickened oil-in-water emulsions, polymer-thickened solids-in-liquid suspensions, and their blends is investigated using a controlled-stress rheometer. The emulsions exhibit a predominantly viscous behaviour at low values of oil concentration in that the loss modulus (G") exceeds the storage modulus (G') over most of the frequency range. At high values of oil concentration, the emulsions exhibit a predominantly elastic behavior. The ratio of storage modulus to loss modulus (G'/G") increases with the increase in oil concentration. Emulsions follow the theoretical model of J. F. Palierne (1990, Rheol. Acta 29, 204) only at low values of oil volume fraction (/=G' over most of the frequency range. The ratio G'/G" varies only slightly with the increase in solids volume fraction. The Palierne model describes the linear viscoelastic properties of suspensions accurately only at low values of solids volume fraction. At high values of solids concentration, the Parlierne model underpredicts the linear viscoelastic properties of suspensions and the deviation increases with the increase in solids concentration. The blends of emulsions and suspensions exhibit strong synergistic effects at low to moderate values of frequencies; the plots of blend modulus versus emulsion content exhibit a minimum. However, at high values of frequency, the blend modulus generally falls between the moduli of pure suspension and pure emulsion. The high-frequency modulus data of blends of emulsions and suspensions are successfully correlated in terms of the modulus ratio versus volume fraction of solids, where modulus ratio is defined as the ratio of blend modulus to pure emulsion modulus at the same frequency. Copyright 2000 Academic Press.     

Electrically developed morphology of carbon nanoparticles in suspensions monitored by in situ optical observations under sinusoidal electric field

In situ optical observations were performed for suspensions composed of carbon nanoparticles under the sinusoidal electric field with an amplitude around 20 kV/mm (volt per micrometer) and various frequencies. For extremely diluted suspensions of mixed fullerenes or multiwalled carbon nanotubes (MWNTs) in a silicone oil, the dark-field optical microscopy was effective for the in situ observation of the particle behavior under the electric field. The nanoparticles in a fullerene suspension under the sinusoidal electric field with a frequency of 100 Hz (in short, 100 Hz electric field) were aggregated to form a rigid spherical microstructure around the halfway between the electrodes. On the other hand, the nanoparticles in an MWNT suspension under 100 Hz electric field were also aggregated but aligned to form a chain-like microstructure which spans the electrodes. Both of the aggregated particles were stable even after the removal of the electric field, and they were redispersed by application of 10 Hz electric field.     

Improved electrorheological effect in polyaniline nanocomposite suspensions

We prepared polyaniline (PANI)/clay composites that are composed of both PANI-clay nanocomposite particles and pure PANI particles. The PANI-clay nanocomposite particles were made during the polymerization process, wherein PANI particles are attached on the surface of exfoliated clay particles modified by an aminosilane group. The PANI/clay composites were used as electrorheological fluids (ERFs) by dispersing them in silicon oil. The PANI-clay nanocomposite particles, which can form columnar structure under an electric field, strongly enhance the mechanical rigidity of the suspensions. The maximum yield stress of the PANI/clay composite suspensions (15 wt% in silicon oil) was 1.6 kPa at 3 kV/mm, while that of pure PANI was 300 Pa at the same electric field. A mechanism to explain the yield behaviors of the PANI-based nanocomposite suspensions is proposed.     

Determination of surface ζ‐potential and isoelectric point of carbon surfaces using tracer particle suspensions

Carbon materials are widely used in a range of applications from biomaterials to sensing and electronics. Many of these applications rely on the ability to control carbon/water interfacial properties, in particular, surface charge density. This work reports a study of the electrokinetic properties of amorphous carbon thin films as a function of pH and surface chemistry. Surface ζ‐potential (SZP) and isoelectric point were determined using the tracer particle method. Initially, the use of sulfonated and amine‐terminated latex bead suspensions as tracer particles for the determination of SZP of reference polymer surfaces was validated. The tracer particle method was then applied to the determination of SZP and isoelectric point of macroscopic carbon surfaces with different surface chemistry. Highly graphitic and sp³‐rich hydrogenated carbon surfaces were found to display negative SZP, as expected for hydrophobic surfaces. The isoelectric point of the most highly graphitic surface was found to be pH_iso = 3.7. Surface oxidation of these films resulted in a decrease of SZP at all pH values and in a downshift of pH_iso to values lower than 1.5, consistently with the presence of surface acidic groups arising from oxidation. Results indicate that the specific choice of acid/base chemistry for the tracer particles does not significantly affect either SZP or pH_iso determinations. These results show that the tracer particle method in combination with widely available latex beads as tracers can be applied for the determination of carbon SZP as a function of pH. Copyright © 2017 John Wiley & Sons, Ltd.