Aqueous Dispersions Of Carbon Nanotubes Research Articles

Effect of Dispersing Carbon Nanotube in Aqueous Solution by Poly-Carboxylic-Based Surfactants on Mechanical and Microstructural Properties as Cementitious Composites.

The development of high-performance concrete using carbon nanotubes (CNTs), which is used in various industries owing to its excellent mechanical properties, has attracted much attention, leading to ongoing research in this area. However, when mixing CNTs into cement paste, there has been limited focus on the dispersibility, and, in most cases, aqueous dispersions of CNTs used in other industrial sectors are used. Because CNTs form the structures of bundles or aggregates owing to their high aspect ratio and van der Waals force between particles, the desired dispersibility cannot be obtained when mixing CNTs in powder form with other materials. Therefore, in this study, we examined the applicability of CNT aqueous dispersions using PC-based plasticizer used in concrete. Aqueous dispersions of CNT using PC-based surfactants are prepared and their properties are compared with those of a PVP-based aqueous dispersion. To analyze the mechanical properties, the compressive strength and flexural strength are measured on the 28th day. Then, the dispersibility and microstructure are analyzed using scanning electron microscopy image analysis, thermogravimetric analysis, and BET (Brunauer-Emmett-Teller) analysis. The analysis results show the enhancement of mechanical properties due to the mixing of the CNT dispersion, and the results confirm the applicability of the proposed CNT aqueous dispersions using PC-based surfactants.

PH- and near-infrared light-responsive, biomimetic hydrogels from aqueous dispersions of carbon nanotubes

pH- and near-infrared light-responsive, biomimetic hydrogels from aqueous dispersions of carbon nanotubes

Efficient Green Synthesis of Highly Concentrated and Stable Carbon Nanotube Aqueous Dispersions for Photothermal Textile Fabrication

To maximize the performance of carbon nanotubes (CNTs) in photothermal conversion textiles, the green and efficient methods for the preparation of highly concentrated and stable aqueous dispersion of CNTs need to be urgently developed. Herein, the aqueous dispersion of CNTs with exceeding high concentration limits (over 100 mg/mL) is synthesized by an eco-friendly one-step hydrothermal method with the assistance of ionic liquid crystals (ILC). CNTs non-covalently wrapped by ILC can exist in various forms, such as well-dispersed dispersion, conductive slurry, thixotropic gel, and deformable dough. Particularly, the highly concentrated dispersion has excellent dispersion stability and remains stable even after 60 days of resting. Due to the cationic head group of ILC, the positively charged dispersion was electrostatically self-assembled to prepare photothermal textiles with excellent mechanical robustness and chemical stability, which can be applied to multiple harsh working conditions. This research shows an efficient and feasible method for the non-destructive dispersion of CNTs at high concentrations and also provides a reference for photothermal conversion applications of CNTs.

Vertically aligned carbon nanotubes/graphene/cellulose nanofiber networks for enhancing electrical conductivity and piezoresistivity of silicone rubber composites

The directional arrangement of a conductive filler is an effective method to improve electrical conductivity of composites. In this paper, aqueous dispersions of carbon nanotubes and graphene were prepared by high-pressure microfluidization technology. After mixing cellulose nanofiber into these dispersions, vertically aligned carbon nanotubes/graphene network foams were prepared using an ice-template assembly method, to which liquid silicone rubber was filled to obtain carbon nanotubes/graphene/silicone rubber composites. Polymethylhydrosiloxane was grafted with 3-(trimethoxysilyl) propyl methacrylate and the resultant copolymer was used as a coupling agent to improve interface interaction between silicone rubber and filler. With increasing carbon nanotubes content, the electrical conductivities of the foams and composites increased. The composite prepared with 4 g CNT and 1 g graphene aqueous dispersions had the conductive percolation threshold of 0.08% and exhibited high conductivity at low filler content. The addition of the copolymer increased the compressive strength of the composites. The composite prepared with 1 g CNT and 4 g graphene aqueous dispersions was encapsulated in an insole as a piezoresistor to effectively detect the number of pedestrian steps, and had a stable output of electrical signal. This work provides a method for preparing conductive silicone rubber composites with low conductive percolation threshold and excellent piezoresistivity.

Smart behaviour of CNT modified adhesive films for carbon fiber composite repair

Epoxy adhesives films were doped by spraying an aqueous dispersion of carbon nanotubes. Sensing capability of carbon fiber reinforced composite coupons with bonded patch repairs was evaluated; several single lap shear and Mode-I fracture energy tests were conducted and their electrical responses were characterized. It was observed that electrical resistance increases with mechanical strain due to tunnelling effect on CNT percolating networks and increases of electrical resistance associated to crack propagations could be also detected. Once the smart behaviour if the adhesive joints was identified by means of mechanical tests in normalized adhesive joined specimens, panels (400 x 400mm) with square co-bonded patches, made using the same curing cycle based on the repaired material one, were prepared using CNT doped adhesive films. These panels were mechanical tested to determine the effect of the doping treatment on the mechanical behaviour of the repairs, at the same time that electric measurements were carried out to identified local failures during testing. Obtained results showed that structural film adhesives could be surface doped with CNT providing sensing capabilities to be used in structural health monitoring of adhesive repairs in composite structures.

Stabilization of pristine and oxidized carbon nanotubes dispersions in acidic and alkaline solutions

The possibility of stabilizing aqueous dispersions of carbon nanotubes (CNTs) using phenol-formaldehyde resin (PFR) and aminocumulene (AC) is shown. The preliminary oxidation of CNTs contributes to their higher solubility in the presence of these stabilizing agents. The concentration of pristine and oxidized CNTs in weakly alkaline solutions containing 2.5 g/L of PFR is 3.0 and 11.4 g/L, respectively. AC promotes the formation of stable dispersions in acidic media with the concentrations of pristine and oxidized CNTs, respectively, 3.3 and 20.4 g/L. A decrease in the effective sizes of agglomerates of both pristine and oxidized CNTs in the presence of PFR and AC has been shown by dynamic light scattering method. According to TG/DSC analysis and Raman spectroscopy data, it was concluded that the oxygen-containing groups of oxidized CNTs interact with the surfactants used. Schemes for the formation of hydrogen and chemical bonds between CNTs and PFR or AС were proposed, which made it possible to explain the effect of dispersion.

Exceeding high concentration limits of aqueous dispersion of carbon nanotubes assisted by nanoscale xylan hydrate crystals

Deacetylated xylan molecules with a low degree of branching can form crystals with water molecules, namely xylan hydrate crystals (XHC), leading to a low water solubility but other unique properties of xylan. However, cutting-edge applications of XHC have never been explored. Surface modified carboxymethylated xylan hydrate crystals (CmXhc) with great amphiphilic and rheological properties were produced through appropriate control of degree of substitution. Nanoscale CmXhc was successfully produced through ultrasonic treatments. Nanoscale CmXhc showed an ability to disperse multi-walled carbon nanotubes (MWCNT) in water with a recorded high CNT concentration of 40 mg/mL and a high dispersion efficiency of 91.7%. The CmXhc can also act as an anchoring agent to bind CNT to paper surfaces making the high concentration dispersion as a conductive paper coating or printing ink. The CmXhc-dispersed MWCNT coated paper demonstrated a high conductivity, specific capacity and capacitance stability, although subject to tuning for improvements, serving as a potential paper-based electrode for supercapacitors.

In English

This review analyses the authors’ recent and related works on electrokinetic properties and colloidal stability of aqueous suspension of multiwalled carbon nanotubes (CNTs) in the presence of surfactants and nanoparticles. Selected adsorptive properties of carbon nanotubes are also considered. The applicability of classical theories of electrophoresis for description of electrophoretic mobility of carbon nanotubes is discussed. Examples on the ζ-potential of CNTs in aqueous suspensions as a function of pH and concentration of electrolytes (KCl, CaCl 2 and AlCl 3 ) are given. Additions of cetyltrimethylammonium bromide (CTAB) cationic surfactant below the critical micelle formation concentration (CMC) values give a reduction and then an overcharging the CNT surface because of accumulation of the surfactant ions in the Stern layer. At concentrations above CMC the substantial drop in ζ is observed. It is due to the shift of the shear plane toward solution as a result of formation of hemi-micelles on the surface. An increase in the mass ratio of artificial mineral Laponite (Lap) in suspension (X) from 0 to 0.4 results in a monotonic decrease of the ζ-potential of CNT + Lap hybrids with reaching its plateau value ≈ –32 mV at X ≥ 0.4 that corresponds to the ζ of “pure” Lap platelets. This evidences the high surface coverage of nanotubes surface with Lap at X ≥ 0.4. The major methods to improve the dispersibility of carbon nanotubes, their colloidal stability and adsorptive properties are briefly discussed, namely: stabilization in mixtures of water and organic solvents; functionalization by chemical treatment; stabilization by additives of surfactants or polymers and hybridization by addition of supplementary stabilizing nanoparticles. CNTs can be significantly debundled in “good” solvents, such as 1-cyclohexyl-2-pyrrolidone, N,N-dimethylformamide, or N-methyl-2-pyrrolidone. It is demonstrated that the dispersibility of CNTs is a complex function of the type of surfactant, its concentration and the surfactant/CNTs ratio. The optimum concentration of CTAB to achieve homogeneous aqueous dispersion of carbon nanotubes was identified to be near the CMC. Additions of CTAB significantly modify the size distribution of CNTs and a sharp transition from small primary aggregates to large secondary aggregates at concentrations above CMC is observed. At optimal concentration of Lap the nanotube particles get well stabilized, and a stepwise increase of sedimentation stability is observed. We have shown also that CNT + Lap hybrids can be effectively used for removal of methylene blue dye from aqueous systems. The kinetics and mechanisms of adsorption are elucidated.

Структурные и спектральные особенности композитов на основе белковых сред с одностенными углеродными нанотрубоками

Исследованы структурные особенности нанокомпозитов, полученных при лазерном облучении водно-белковых сред с одностенными углеродными нанотрубками (ОУНТ), электродуговым (ОУНТI) и газофазным методами (ОУНТII). С помощью спектроскопии комбинационного рассеяния нанокомпозитов определен нековалентный характер взаимодействия нанотрубок с молекулами белков. Белковая составляющая в нанокомпозитах подверглась необратимой денатурации и может выступать в качестве связующего биосовместимого материала, который является источником аминокислот для биологических тканей при имплантации нанокомпозитов в организм. Образцы, изготовленные из ОУНТI, с меньшим диаметром и длиной имели наиболее однородную структуру. При увеличении концентрации от 0.01 до 0.1 % происходило увеличение среднего размерамикропор от 45 до 85 мкм и пористости образца в общем с 46 до 58 %. При этом доля открытых пор для двух типов концентраций ОУНТI составила 2 % от общего объема композита. В нанокомпозитах на основе ОУНТI показано наличие мезопор. Увеличение концентрации нанотрубок привело к уменьшению удельных значений поверхности и объема пор образца. Исследованные нанокомпозиты могут использоваться в качестве тканеинженерных матриц для восстановления объемных дефектов биологических тканей
 
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A new approach for the achievement of stable aqueous dispersions of carbon nanotubes.

A novel methodology to prepare stable aqueous dispersions of raw single- and multi-walled carbon nanotubes is reported, based on dispersions previously prepared in tetrahydrofuran containing a phenol that donates electrons to nanotubes and provides colloidal stability through electrostatic repulsion. A proposed mechanism for the stabilization of the dispersions is presented. Conductive and transparent thin films are prepared through a liquid/liquid interfacial route starting from these dispersions.

Stabilization of the aqueous dispersion of carbon nanotubes using different approaches

This paper presents experimental investigations on aqueous dispersion of multi-walled carbon nanotubes (MWCNTs). Three experimental approaches are considered to improve MWCNTs dispersion; through functionalization of MWCNTs (1) with surfactants, (2) with oxidative acid treatment and (3) with metal decoration. The first approach investigated the dispersion stability of MWCNTs using different surfactants. In the second approach, surface of MWCNTs is functionalized through nitric acid treatment to facilitate the dispersion of MWCNTs. In the third approach, MWCNTs are decorated with silver nanoparticles and their dispersion behavior is investigated. In the experiments with surfactant addition, the ideal surfactant type and concentration are found as acacia gum at 1 surfactant:MWCNTs weight ratio, which yielded the highest zeta potential value of 26.7 mV. The second approach yielded an improved dispersion stability by visual observation of the fluid over a period of three months with no trace of sedimentation. Visual observation of the fluids prepared using silver-decorated MWCNTs showed a weak dispersion behavior. Thermal conductivity enhancement of the nanofluids at 0.1 wt% nanoparticle loading are calculated as 5.84% for silver-decorated MWCNT nanofluids, 8.14% for acid-functionalized MWCNT nanofluids and 8.85% for surfactant-functionalized MWCNT nanofluids. Functionalization with surfactant and oxidative acid treatment are found as the two useful methods for the stability and enhanced thermal conductivity of MWCNT dispersions.

Structure and Biochemical Study of Nanocomposite Bioconstruction for Restoration of Bone-cartilaginous Defects

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Highly Concentrated Aqueous Dispersions of Carbon Nanotubes for Flexible and Conductive Fibers

Dispersing carbon nanotubes (CNTs) using surfactants into water requires ultrasonication that supplies mechanical energy to debundle and exfoliate CNTs. However, sonication is known to damage CNTs and to cut them into short fragments. Also, the CNT concentration in water dispersion is typically limited to up to 1.0 wt %. Here, we show that by using a sulfuric acid pretreatment, we can enhance the debundling of CNTs and reduce subsequent sonication to achieve homogeneous dispersions without damaging CNTs. Additionally, using a progressive and controlled dialysis, we are able to increase the CNT concentration up to 1.8 wt %. We demonstrate that such highly concentrated dispersions can be used as spin dopes to fabricate continuous fibers. Our fibers have an electrical conductivity up to 580 kS/m, a tensile strength of ∼1 GPa, and a Young’s modulus of 123 GPa, exceeding the mechanical properties of related fibers made from conventional surfactant-stabilized dispersions of sonicated CNTs.

Carbon Nanotube-Doped Adhesive Films for Detecting Crack Propagation on Bonded Joints: A Deeper Understanding of Anomalous Behaviors.

A novel nanoreinforced adhesive film has been developed to detect adhesive deformation and crack propagation along the bonding line by means of the electrical response of the material. Adhesive films were doped by spraying an aqueous dispersion of carbon nanotubes (CNTs) over the surface. To determine the sensitivity of bonded joints, single lap shear (SLS) and mode-I fracture energy tests have been carried out while their electrical response has been measured. It has been found that CNT-doped adhesive films are able to detect adhesive deformation and final failure for SLS specimens and crack initiation and propagation along the bonding line for mode-I specimens with a high sensitivity. Sudden increases on electrical resistance are correlated to a rapid growing of the crack length due to instability on crack propagation in a tick-slip case, whereas specimens with a more uniform crack propagation are linked to a steadier increase on electrical resistance, and both of them are properly correlated to the mechanical response. By analyzing more in detail the electrical response and comparing with theoretical approaches, the stick-slip behavior is associated with the presence of porosity and lack of adhesives because of possible manufacturing issues such as adhesive overflowing. These statements are also validated by microstructural analysis. Therefore, the potential and applicability of the proposed adhesive films for evaluating the structural integrity has been demonstrated.

Creating Carbon Nanotubes Microenvironment in Surfactant Water Solutions

The infrared absorption spectra of aqueous dispersions of carbon nanotubes in the presence of surfactants and alkali metal salts in the frequency range from 1000 cm-1 to 3000 cm-1 have been studied. The possibility of controlling the characteristics of local environment of carbon nanotubes by varying external electrolyte and modulation the surfactant micelle structure has been shown.

Direct Aqueous Dispersion of Carbon Nanotubes Using Nanoparticle-Formed Fullerenes and Self-Assembled Formation of p/n Heterojunctions with Polythiophene.

Single-walled carbon nanotubes (SWCNTs) have received much attention because of their potential in optoelectronic applications. Pristine SWCNTs exhibit substantial van der Waals interactions and hydrophobic characteristics, so precipitation occurs immediately in most organic solvents and water. Highly toxic and hazardous chemicals are often used to obtain well-dispersed SWCNTs. Developing environmentally friendly processing methods for safe and practical applications is a great challenge. Here, we demonstrate direct exfoliation of SWCNTs in pure water only with n-type semiconducting fullerene nanoparticles. The resultant SWCNTs can be well-dispersed in water, where they remain essentially unchanged for several weeks. Adding an aqueous solution of p-type semiconducting water-soluble polythiophene yields self-assembled p/n heterojunctions between polythiophene and the nanoparticles. The aqueous-dispersed SWCNTs yield photocurrent responses in solution-processed thin films as a potential application of water-dispersed carbon nanomaterials.

Lignin-assisted double acoustic irradiation for concentrated aqueous dispersions of carbon nanotubes

Carbon nanotube (CNTs) dispersion is one of the most challenging tasks for many applications. Lignin-assisted double sonication represents a low-cost and renewable alternative to prepare stable and concentrated suspensions of individualized CNTs.

Production of hierarchical all graphitic structures: A systematic study

We report the production of hierarchical all graphitic structures through a systematic study involving the use of wet chemical treatments for dip coating of carbon fibers (CFs) for surface grafting with multiwalled carbon nanotubes (CNTs). Realization of a thin homogeneous veil of CNTs onto the CF surface was achieved through an extensive parametric survey. Optimization of aqueous dispersions of CNTs eliminated the need for oxidation of the CF surface. The effects of chemical processes onto the surface and structural characteristics of the involved graphitic species were evaluated via thermogravimetric analysis, and X-ray photoelectron, infrared and Raman spectroscopies. The dielectric properties of the produced CNT aqueous dispersions were monitored via electrochemical impedance spectroscopy. A final assessment of the produced hierarchical CFs was performed through scanning electron microscopy.

Attenuation of ultrasound reflects orientation of carbon nanotubes in aqueous dispersion

Ultrasound attenuates when propagating through aqueous dispersions of carbon nanotubes. We established a significant difference in the ultrasound attenuation frequency spectra for the nanotubes oriented either along or across the ultrasound beam. This effect can be used for calculating geometrical and rheological properties of nanofiber materials dispersed in liquids.

Overcoming the quality–quantity tradeoff in dispersion and printing of carbon nanotubes by a repetitive dispersion–extraction process

Dispersion-printing processes are essential for the fabrication of various devices using carbon nanotubes (CNTs). Insufficient dispersion results in CNT aggregates, while excessive dispersion results in the shortening of individual CNTs. To overcome this tradeoff, we propose here a repetitive dispersion–extraction process for CNTs. Long-duration ultrasonication (for 100min) produced an aqueous dispersion of CNTs with sodium dodecylbenzene sulfonate with a high yield of 64%, but with short CNT lengths (a few μm), and poor conductivity in the printed films (∼450Scm−1). Short-duration ultrasonication (for 3min) yielded a CNT dispersion with a very small yield of 2.4%, but with long CNTs (up to 20–40μm), and improved conductivity in the printed films (2200Scm−1). The remaining sediment was used for the next cycle after the addition of the surfactant solution. 90% of the CNT aggregates were converted into conductive CNT films within 13 cycles (i.e., within 39min), demonstrating the improved conductivity and reduced energy/time requirements for ultrasonication. CNT lines with conductivities of 1400–2300Scm−1 without doping and sub-100μm width, and uniform CNT films with 80% optical transmittance and 50Ω/sq sheet resistance with nitric acid doping were obtained on polyethylene terephthalate films.