Interaction Forces Between Graphitic Carbon Black Surfaces Coated with Polymers Using Atomic Force Microscopy

Carbon black dispersions are stabilized using polymeric dispersants. The stabilization is provided by adsorbed polymer layers around surfaces through interaction forces. Therefore, it is valuable to measure the interaction forces between bare and polymer-coated surfaces using atomic force microscopy to predict the behavior of dispersions. Three polymeric dispersants (Hypermer LP1, Hypermer B246, and OLOA 11000) are used in the present work to disperse the graphitic carbon black particles in an organic solvent, decaline. Hypermer B246 and OLOA 11000 produced repulsive interactions and, hence, are effective stabilizers for carbon black surfaces. Hypermer LP1 produced attractive interactions, making it an ineffective stabilizer for carbon black. Attractive interactions were also observed in blank dispersions. The experimentally determined interaction curves are compared with theoretical curves, the Derjaguin approximation. The repulsive steric interactions are also analyzed quantitatively based on the Alexander and de Gennes scaling law.     

Rheological Scaling Methods in Food Matrices Containing Stabilizer

Relative viscosity, Peclet, and Reynolds scaling methods were used in various food matrices consist of tragacanth gum (TG) (0.5, 1% wt), Oleic acid (5, 10% v/v) and WPI (2, 4% wt) and the best scaling law was selected. As these emulsions are non-Newtonian, they do not obey the usual, simple, scaling laws. When the apparent viscosity is reduced to relative viscosity of the medium at zero shear rate, a distinct reduced flow curve is obtained, regardless of TG, oleic acid, and WPI concentrations. This will lead to a technique of simplifying complex non-Newtonian flow curves and therefore predicting the rheological flow curves and fluid mechanics when different modifiers are added to food emulsions. The flow behavior of all samples was successfully modeled with the Cross model, Power law model, and Ellis model, and Power law model was found as the better model to describe the flow behavior of dispersions. Results showed that both G′ and G″ increased with TG, oleic acid and WPI concentrations. However, the viscoelastic behavior was mainly governed by the TG content.     

Effects of trace water on charging of silica particles dispersed in a nonpolar medium

This paper presents an investigation of the effects of trace water on the charging of silica (SiO(2)) particles dispersed in a nonpolar medium. There are a growing number of applications that seek to use electrostatic effects in apolar media to control particle movement and aggregation stability in such systems. One factor that is often overlooked in the preparation of nonpolar colloidal dispersions is the amount of water that is introduced to the system by hygroscopic particles and surfactants. The amount and location of this water can have significant effects on the electrical properties of these systems. For nonpolar surfactant solutions it has been shown that water can affect the conductivity, and it has been speculated that this is due to swelling of the polar cores of inverse micelles, increasing the fraction of them that are charged. Some studies have suggested that particle surface charging may also be sensitive to water content, but a clear mechanism for the process has not been fully developed. The situation with particles is further complicated by the fact that it is often unclear whether the water resides on the particle surfaces or in the polar cores of inverse micelles. The current work explores not only the effect of water content on reverse micelle and particle charging but seeks to differentiate between water bound to the particles and water located in the micelles. This is accomplished by measuring the solution conductivity and the electrophoretic mobility of silicon dioxide particles dispersed in solutions of Isopar-L and OLOA 11000. The water content is determined for both the dispersion and the supernatant after centrifuging the particles out. It is found that at equilibrium the majority of the water in the system adsorbs to the surface of the hygroscopic silica particles. In addition, the effect of water on particle electrophoretic mobility is found to be dependent on surfactant concentration. At small OLOA concentrations, additional water results in an increase in particle mobility due to increased particle charging. However, at large OLOA concentrations, additional water leads to a decrease in particle mobility, presumably as a result of increased electrostatic screening or neutralization. Thus, particle charging and electrophoretic mobility in an apolar surfactant solution are found to be highly sensitive to both the total water content in the system and to its concentration relative to the amount of surfactant present.     

Preparation of stable dispersion of graphene using copolymers: dispersity and aromaticity analysis

In this study, effectiveness of non-ionic block copolymers such as Lugalvan BNO12 and Triton X series (Triton X100 & Triton X405) has been reported for graphene dispersion in aqueous solutions. Stability of the aqueous graphene dispersions is investigated using UV–visible spectroscopy, Rheological, and Conductivity studies. Adsorption isotherms are constructed to determine the amount of polymers adsorbed on the surface of graphene by the spectroscopic analysis. Lugalvan BNO12 has been found to be adsorbed in higher amounts on the graphene surface compared to the Triton X series polymers. Thermogravimetric analysis (TGA) and Fourier Transform Infrared (FTIR) Spectroscopy investigations indicated grafting of polymers chains to the graphene surfaces. The dispersions prepared with optimum concentrations (as determined from adsorption isotherms) of polymers have shown lower viscosity and conductivity values. Lugalvan BNO12 has been found to be a better stabilizer for graphene than the Triton X series dispersants because the former contains two aromatic rings in its structure that acts as an anchoring group and helps in the stabilization of graphene dispersion in comparison to the single aromatic group in the Triton X series. The experimental results reported have shown that the aromaticity of polymeric dispersants plays significant role in the aqueous graphene dispersions. The non-ionic block copolymers that assisted dispersed graphene are potential candidates for the fabrication of various devices such as sensors, batteries, and supercapacitors applications.     

Intrinsically conducting polymer blends

Polyaniline (PANI) doped with different dopants (HCl, dodecyl benzene sulfonic acid, (+)‐Camphor‐10 sulfonic acid, dinonyl naphthalene disulfonic acid) was synthesized by chemical oxidation method. The FTIR studies indicated that the back bone structure of doped PANI was similar. Thermal stability was evaluated in nitrogen atmosphere by dynamic thermogravimetry and PANI‐HCl sample showed minimum weight loss below 400°C. The electrical conductivity of PANI was not affected by the structure of dopants. The microwave absorption studies of several polymers blends containing PANI‐HCl and/or carbon black were also carried out by using wave guide technique.     

Modeling the effect of molecular architecture of comb polymers on the behavior of Al2O3 dispersions using charge/composition factors (CCF)

In this work, we study the effect of periodicity and PEO side-chain length in four PMAA-PEO (sodium salt) comb polymers with known molecular architecture on Al₂O₃ colloidal dispersions in DI water. We introduce here charge composition factors (CCF) representing charge density of the comb polymers defined as (number of charged units in a repeating unit)/(molecular weight of a repeating unit). We find, for the first time to our knowledge, that the CCF can be used along with dispersant dosage to obtain explicit functions predicting the conductivity of the dispersants in solution, the zeta potential behavior during dispersant titrations, and the isoelectric point (IEP) of the dispersions. In addition, the dosage normalized by the CCF provides a basis for comparison for the dispersants to elucidate the trends found in adsorption and potentiometric titrations. Thus, the CCF can be used as a tool for the design of improved and new comb polymer molecular architectures.     

Modeling and Scaling of Food Dispersions

Scaling laws, determined by dimensional analysis, have been used to make experimental predictions of constitutive shear-flow rheology. This study aimed to scale and model the flow curves of various suspensions consisting of xanthan gum (0.5, 1 wt%) and WPI (2, 4 wt%), and to determine the best-scaling law and rheological model. The scaling methods were relative viscosity, Péclet number, and Reynolds number. When the apparent viscosity is reduced relative to the viscosity of the medium at zero-shear rate, a distinct reduced flow curve is obtained, regardless of xanthan and WPI concentrations. This study tough to develop a technique of simplifying complex non-Newtonian flow curves and, therefore, predicting the rheological flow curves and fluid mechanics when different modifiers are added to food suspensions. The flow behavior of all samples was successfully modeled with the power law, Ellis, and Cross models; the power law model best described the flow behavior of dispersions. Results showed that both G′ and G″ increased with xanthan and WPI. However, viscoelastic behavior was mainly governed by the xanthan gum content.     

A novel approach for preparation of conductive hybrid elastomeric nano‐composites

Since the discovery of carbon nanotubes (CNTs) and intrinsically conductive polymers, such as polyaniline (PANI) some research has focused on the development of novel hybrid materials by combining CNT and PANI to achieve their complementary properties. Electrically conductive elastomer nano‐composites containing CNT and PANI are described in the present investigation. The synthesis procedure includes in‐situ inverse emulsion polymerization of aniline doped with dodecylbenzene sulfonic acid in the presence of CNT and dissolved styrene‐isoprene‐styrene (SIS) block copolymer, followed by a precipitation–filtration step. The synthesis step is carried out under ultrasonication. The resulting uniform SIS/CNT/PANI dispersions are stable for long time durations. The incorporation of CNT/PANI in the SIS elastomeric matrix improves thermal, mechanical and electrical properties of the nano‐composites. The formation of continuous three‐dimensional CNT/PANI network, assumed to be responsible for enhancement of the resulting nano‐composite properties, is observed by HRSEM. A relatively low percolation threshold of 0.4 wt.% CNT was determined. The Young's modulus of the SIS/CNT/PANI significantly increases in the presence of CNT. High electrical conductivity levels were obtained in the ternary component systems. Copyright © 2013 John Wiley & Sons, Ltd.     

Preparation of conductive PTFE nanocomposite containing multiwalled carbon nanotube via latex heterocoagulation approach

Conductive poly(tetrafluoroethylene) (PTFE) composites containing surface-modified multiwalled carbon nanotubes (MWCNTs) were prepared by a simple heterocoagulation process in water. Two different types of MWCNT were used and compared: carboxylated MWCNT and cetyltrimethyl ammonium bromide (CTAB)-stabilized MWCNT. Aqueous PTFE dispersion was mixed with the well-dispersed MWCNT dispersions and they were heterocoagulated with the aid of a flocculant, polyaluminum chloride at an elevated temperature. After particle growth and successive stabilization step, particulated PTFE/MWCNT composites were prepared in the size range of 10–100 μm. The MWCNT-containing PTFE composites have improved thermal stability and electrical conductivity. Importantly, the percolation threshold for the electrical conductivity was achieved at a low concentration of MWCNT using this heterocoagulation process.     

ADSORPTION BEHAVIOUR AND RHEOLOGICAL PROPERTIES OF NON-AQUEOUS LANTHANUM CHROMITE SUSPENSIONS

Adsorption studies of monosubstituted benzene molecules with various functional groups on doped lanthanum chromite/cyclohexane surface have been performed. The results from the adsorption study can be used in selecting appropriate anchoring groups on the dispersant. It was found that high amount of O relative lo La on the LaCrO₃ surface correlated with high amounts of adsorbed benzoic acid. Increase in the La content relative to the O on the powder surface increased the amount of adsorbed benzylamine. The high amount of benzoic acid adsorbed on 20% Ca-doped lanthanum chromite powder (Al)lated well with good colloidal stability caused by a carboxylic acid containing dispersant. Rheology experiments showed that a low degree of agglomeration is obtained using only a small amount of the carboxylic acid containing dispersant (Hypermer LP1). Etectrophoretic mobility measurements in water of this powder coated with the LP1 dispersant indicated electrosteric stabilisation.     

LDPE／CPE／炭黑三相复合导电体系的亚微形态和导电性能

对ＬＤＰＥ／ＣＰＥ／炭黑三相复合导电体系的亚微形态和导电性能进行了研究。实验发现,该体系的亚微形态在共混比ＬＤＰＥ／ＣＰＥ大于和小于５０／５０时为典型的“海－岛”结构,在５０／５０时,为两相连续交错“互锁”结构;在共混比大于５０／５０时,ＬＤＰＥ／ＣＰＥ炭黑复合体系的导电性能较单一的ＬＰＤＰＥ树脂与炭黑复合体系的高２－５个数量级。     

Volume‐exclusion effects in polyethylene blends filled with carbon black,graphite, or carbon fiber

Conductive polymer composites possessing a low percolation‐threshold concentration as a result of double percolation of a conductive filler and its host phase in an immiscible polymer blend afford a desirable alternative to conventional composites. In this work, blends of high‐density polyethylene (HDPE) and ultrahigh molecular weight polyethylene (UHMWPE) were used to produce ternary composites containing either carbon black (CB), graphite (G), or carbon fiber (CF). Blend composition had a synergistic effect on electrical conductivity, with pronounced conductivity maxima observed at about 70–80 wt % UHMWPE in the CB and G composites. A much broader maximum occurred at about 25 wt % UHMWPE in composites prepared with CF. Optical and electron microscopies were used to ascertain the extent to which the polymers, and hence filler particles, are segregated. Differential scanning calorimetry of the composites confirmed that the constituent polymers are indistinguishable in terms of their thermal signatures and virtually unaffected by the presence of any of the fillers examined here. Dynamic mechanical analysis revealed that CF imparts the greatest stiffness and thermal stability to the composites. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1013–1023, 2002     

Reduced percolation thresholds of immiscible conductive blends

The DC conductivity of polymer blends composed of poly(ethylene‐co‐vinyl acetate) (EVA) and high density polyethylene (HDPE), where a conductive carbon black (CB) had been preferentially blended into the HDPE, were investigated to establish the percolation characteristics. The blends exhibited reduced percolation thresholds and enhanced conductivities above that of the individually carbon filled HDPE and EVA. The percolation threshold of the EVA/HDPE/CB composites was between 3.6 and 4.2 wt % carbon black, where the volume resistivity changed by 8 orders of magnitude. This threshold is at a significantly lower carbon content than the individually filled HDPE or EVA. At a carbon black loading of 4.8 wt %, the EVA/HDPE/CB composite exhibits a volume resistivity which is approximately 14 and 11 orders of magnitude lower than the HDPE/CB and EVA/CB systems, respectively, at the same level of incorporated carbon black. The dielectric response of the ternary composites, at a temperature of 23°C and frequency of 1 kHz, exhibited an abrupt increase of ca. 252% at a carbon concentration of 4.8 wt %, suggesting that the percolation threshold is somewhat higher than the range predicted from DC conductivity measurements. Percolating composites with increasing levels of carbon black exhibit significantly greater relative permittivity and dielectric loss factors, with the composite containing 6 wt % of carbon black having a value of ϵ′ ≈ 79 and ϵ″ ≈ 14. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1899–1910, 1999     

Grafting of hyperbranched cyclotriphosphazene polymer onto silica nanoparticle and carbon black surfaces

The surface grafting of hyperbranched cyclotriphosphazene polymer onto silica nanoparticles and carbon black was investigated. The grafting of hyperbranched cyclotriphosphazene polymer onto these surfaces was achieved by the repeated reactions of hexachlorocyclotriphosphazene with hexamethylenediamine from surface amino groups and sodium carboxylate groups, respectively. The percentage of grafting onto silica and carbon black surfaces exceeded 760 and 390%, respectively. However, it proved difficult to achieve the theoretical growth of cyclotriphosphazene polymer from these surfaces because of steric hindrance. The introduction of sulfonic acid groups was successfully achieved by the reaction of terminal chlorophosphazene groups of the hyperbranched polymer‐grafted silica and carbon black with sulfanilic acid. The content of sulfonic acid groups introduced onto silica and carbon black surfaces was 4.98 mmol/g and 5.70 mmol/g, respectively. The sulfonated cyclotriphosphazene polymer‐grafted carbon black was extremely hydrophilic, yielding stable colloidal dispersions in polar solvents. The sulfonated cyclotriphosphazene polymer‐grafted silica and carbon black showed ionic conductivity, with the conductance increasing exponentially with increasing relative humidity and temperature. This study may offer important leads in the application of silica nanoparticles and carbon black in polymeric membranes for fuel cells. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4218–4226, 2008     

Dispersion of single‐walled carbon nanotubes using nucleobase‐containing poly(acrylamide) polymers

Single‐walled carbon nanotubes (SWNTs) possess extraordinary properties, but suffer from poor solubility and a lack of purity. Of the possible routes available to solubilize and purify nanotube samples, the use of noncovalent functionalization is ideal as carbon nanotube properties are not deleteriously affected. A multitude of different dispersants have been investigated thus far, but of particular interest is deoxyribonucleic acid (DNA), which has previously been demonstrated to effectively separate metallic and semiconducting carbon nanotubes. Here, we investigate the ability of synthetic nucleobase‐containing poly(acrylamide) polymers to produce stable nanotube dispersions in organic solvents. Polymers bearing different nucleobase and backbone structures, as well as block copolymers with different block sequences were investigated. Polymer:SWNT mass ratios and solvent compositions were optimized for the nucleobase‐functionalized polymers, and semiconducting and metallic SWNT populations were identified by a combination of UV‐Vis‐NIR absorption, Raman, and fluorescence spectroscopy. These results demonstrate the capacity for synthetic DNA analogues to disperse SWNTs in organic media. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2611–2617     

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 Chain Microstructure Magnetic Emulsions in Magnetic Field

The work deals with the experimental study of the emulsion whose dispersion medium is a magnetic fluid while the disperse phase is formed by a glycerin-water mixture. It is demonstrated that under effect of a magnetic field chain aggregates form from the disperse phase drops. Such emulsion microstructure change affects its macroscopic properties. The emulsion dielectric permeability and specific electrical conductivity have been measured. It is demonstrated that under the effect of relatively weak external magnetic fields (～1 kA/m) the emulsion electrical parameters may change several fold. The work theoretically analyzes the discovered regularities of the emulsion electrical properties.     

A Review Featuring Fabrication,Properties and Applications of Carbon Nanotubes (CNTs) Reinforced Polymer and Epoxy Nanocomposites

Carbon nanotubes (CNTs) have long been recognized as the stiffest and strongest man-made material known to date.In addition,their high electrical conductivity has roused interest in the areas of electrical appliances and communication related applications.However,due to their miniature size,the excellent properties of these nanostructures can only be exploited if they are homogeneously embedded into light-weight matrices as those offered by a whole series of engineering polymers.In order to enhance their chemical affinity to engineering polymer matrices,chemical modification of the graphitic sidewalls and tips is necessary.The mechanical and electrical properties to date of a whole range of nanocomposites of various carbon nanotube contents are also reviewed in this attempt to facilitate progress in this emerging area.Recently,carbonaceous nano-fillers such as graphene and carbon nanotubes (CNTs) play a promising role due to their better structural and functional properties and broad range of applications in every field.Since CNTs usually form stabilized bundles due to van der Waals interactions,they are extremely difficult to disperse and align in a polymer matrix.The biggest issues in the preparation of CNTs reinforced composites reside in efficient dispersion of CNTs into a polymer matrix,the assessment of the dispersion,and the alignment and control of the CNTs in the matrix.An overview of various CNT functionalization methods is given.In particular,CNT functionalization using click chemistry and the preparation of CNT composites employing hyperbranched polymers are stressed as potential techniques to achieve good CNT dispersion.In addition,discussions on mechanical,thermal,electrical,electrochemical and applications ofpolymer/CNT composites are also included.     

A Novel Method for Preparing Polyurethane Based Conductive Composites with Low Percolation Threshold

A novel method for preparing conductive carbon black filled polymer composites with low percolation threshold from polyurethane emulsion are reported in this paper. The experimental results indicate that with a rise in carbon black concentration the insulator-conductor transition in the emulsion blended composites occurs at 0.8-1.4vol%. In contrast, the solution blended composites exhibit drastic increase in conductivity at conducting filler fraction as high as 12.3-13.3vol%. It is demonstrated that the composites microstructure rather than chemical structure of the matrix polymer predominantly determines the electrical conduction performance of the composites.