Carbon Nanotubes In Organic Solvents Research Articles

Preparation of Electrochemical Biosensor Systems for the Analysis of Biological Objects: a Reasonable Choice of Modifications of the Working Surface of Electrodes for Performing Research in the "Smart Electrode" Mode

The electrochemical method of analysis of biological objects based on the reaction of electro-oxidation/electro-reduction of molecules is considered. Materials and complex systems for modifying electrodes as well as methods for producing modified electrodes to increase the sensitivity of recording the flow of electrochemical reactions on the surface of the electrodes are described. Methods of electrode modifications based on synthetic lipid-like didodecyldimethylammonium bromide, gold and silver nanoparticles, one-dimensional nanoparticles based on lead compounds, titan oxide nanoparticles, dispersions of carbon nanotubes in organic solvents, in polymers with different chemical structure are considered. It is shown that the appropriate functionalization of the working electrode surface makes it possible to increase the sensitivity of the electrochemical biosensor system and decrease the limit of detection. The results are presented in the form of an algorithm applicable for selection the beneficial type of modified electrode for the corresponding electrochemical reaction and biosample analysis.

Scalable Alignment of Carbon Nanotubes via Shear

Semiconducting carbon nanotubes must be aligned at optimal packing densities prior to the integration of this material into transistors, however, this has been historically difficult to accomplish on a wafer-scale. Here, we use solution-based shear to deposit continuous films of well-aligned, individualized, semiconducting nanotubes across target substrates. We are able to generate shear up to 10,000 s-1, which serves to align the carbon nanotubes, by forcing the carbon nanotubes in organic solvent through sub-mm tall channels. To investigate the effect of the alignment on charge transport properties, transistors are fabricated parallel and perpendicular to the alignment direction. The parallel transistors perform with 7× faster mobility while still retaining a high on/off ratio of 105. Optimized experimental conditions enable alignment within a ±32°, at 50 nanotubes µm-1, on a 10 × 10 cm2 substrate.

Assembly of aligned semiconducting carbon nanotubes in organic solvents via introducing inter-tube electrostatic repulsion

The main challenge for application of solution-derived carbon nanotube (CNT) in high performance field-effect transistor is how to obtain the aligned film with full surface coverage and uniform inter-tube pitch. Herein, a wafer-scale aligned array of s-SWCNTs can be assembled using the combination of the introduced inter-tube electrostatic repulsion and an improved “bi-phasic” dip-coating method. By using a conjugated molecule with positive charge to modify the charge on the surface of s-SWCNTs dispersed in organic solvents, the inter-tube electrostatic repulsion was correspondingly introduced. The inter-tube electrostatic repulsion can significantly inhibit the agglomeration of s-SWCNTs in the formation process of the aligned SWCNT films. Significantly, the aligned SWCNT thin film exhibits excellent surface coverage and anisotropy over the 3 inch aligned area.

Spatially Selective, High-Density Placement of Polyfluorene-Sorted Semiconducting Carbon Nanotubes in Organic Solvents.

High-performance logic based on carbon nanotubes (CNTs) requires high-density arrays of selectively placed semiconducting CNTs. Although polymer-wrapping methods can allow CNTs to be sorted to a >99.9% semiconducting purity, patterning these polymer-wrapped CNTs is an outstanding problem. We report the directed self-assembly of polymer-coated semiconducting CNTs using self-assembled monolayers that bind CNTs into arrays of patterned trenches. We demonstrate that CNTs can be placed into 100 nm wide HfO2 trenches with an electrical connection yield as high as 90% and into 50 nm wide trenches with a yield as high as 70%. Our directed self-assembly method is an important step forward in pitch scaling.

Dispersibility of carbon nanotubes in organic solvents: do we really have predictive models?

Predicting the physico-chemical properties of carbon nanotubes (CNTs) is highly demanding owing to tedious experimental efforts involved in their determination. Dispersibility of CNTs in organic solvents is one such property; however, studies involving its quantitative prediction are quite scarce and highly questionable, particularly, when the real external predictivity is desired. This work examines the real external predictivity of the existing models as well as those developed in the present work (using quantum-chemical descriptors) for the dispersibility of single-walled CNTs (SWCNTs). The real external predictivity is assessed on the basis of state-of-the-art external validation parameters obtained by employing an external prediction set which is not exposed to the model used for the prediction. Notably, most of the present and existing models pass through the internal validation, but unfortunately, barring some exception of poly-parameter models, most of the models fail when it comes to the external validation. Their failure was attributed to the descriptors employed which are in fact based on the gas-phase single molecular structure of organic solvents as well as based on the implicit solvent methods. A future approach towards the predictive models for the dispersibility of CNTs is suggested based on the explicit solvent methods.

Preparation of Reactoplastic Nanomodified Polymer Composites. Part 3. Methods for Dispersing Carbon Nanotubes in Organic Solvents and Liquid Polymeric Media (Review)

Effective methods for dispersing carbon nanotubes in organic solvents and liquid polymeric media were analyzed. The relationship of these methods for improving the operational performance of nanomodified polymer composites was studied. It was shown that the conditions necessary to create such materials are a small size and a distribution of carbon nanofiller particles as uniform as possible in the liquid polymeric matrix. The tendency of the carbon nanofiller to aggregate prevented the preparation of stable dispersions in water and organic solvents. Therefore, effective methods for facilitating aggregate disintegration, including use of low-frequency ultrasound, are being actively pursued.

Modeling the Dispersibility of Single Walled Carbon Nanotubes in Organic Solvents by Quantitative Structure-Activity Relationship Approach.

The knowledge of physico-chemical properties of carbon nanotubes, including behavior in organic solvents is very important for design, manufacturing and utilizing of their counterparts with improved properties. In the present study a quantitative structure-activity/property relationship (QSAR/QSPR) approach was applied to predict the dispersibility of single walled carbon nanotubes (SWNTs) in various organic solvents. A number of additive descriptors and quantum-chemical descriptors were calculated and utilized to build QSAR models. The best predictability is shown by a 4-variable model. The model showed statistically good results (R2training = 0.797, Q2 = 0.665, R2test = 0.807), with high internal and external correlation coefficients. Presence of the X0Av descriptor and its negative term suggest that small size solvents have better SWCNTs solubility. Mass weighted descriptor ATS6m also indicates that heavier solvents (and small in size) most probably are better solvents for SWCNTs. The presence of the Dipole Z descriptor indicates that higher polarizability of the solvent molecule increases the solubility. The developed model and contributed descriptors can help to understand the mechanism of the dispersion process and predictorganic solvents that improve the dispersibility of SWNTs.

Dispersion of carbon nanotubes in organic solvent by commercial polymers with ethylene chains: Experimental and theoretical studies

We demonstrate the possible candidate dispersion agents that can uniformly disperse carbon nanotubes (CNTs) into organic solvent, from among commercially available polymers. We find that CNTs were well dispersed into dimethylacetamide with the use of polystyrene, poly(vinyl chloride), and poly(vinyl pyrrolidone) as dispersion agents. Theoretical calculations revealed that the dispersibility of these polymers arises from the moderate strength and preferential directionality of the interactions between the CNTs and the polymers.

Dispersion of Multiwall Carbon Nanotubes in Organic Solvents through Hydrothermal Supercritical Condition

Multiwall carbon nanotube (MWCNT) composite materials require careful formulation of processing methods to ultimately realize the desired properties. Until now, controlled dispersion of MWCNT remains a challenge, due to strong van der Waals binding energies associated with the MWCNT aggregates. In the present study, an effort has been made to disperse MWCNTs in organic solvents like dichloromethane, ethanol, isopropyl alcohol, and hexane through hydrothermal reaction. Dichloromethane is considered the best solvent for the dispersion of MWCNTs. The characterizations were carried out to find the dispersion design, particle size, and stabilization, which clearly indicate that the desired properties of MWCNTs have been achieved.

Mechanical Reinforcement of Polybenzoxazole by Carbon Nanotubes through Noncovalent Functionalization

Polybenzoxazole (PBO) reinforced with carbon nanotubes (CNTs) is of great interest in the field of polymer composites because PBO and CNTs possess the highest-level mechanical properties among polymers and filler materials, respectively. However, the insolubility of PBO and the CNTs makes it difficult to develop a CNT/PBO composite in a solvent except for strong acids. In this study, we describe a novel strategy to design and prepare a CNT/PBO composite; namely, a method using a PBO precursor having an excellent solubility in organic solvents. We discovered that a PBO precursor wraps CNTs though a strong interfacial interaction between the CNT surfaces and the PBO precursor that enables the dispersion of the CNTs in organic solvents. By this method, a CNT/PBO precursor composite film was easily obtained from the CNT/PBO composite solution, and by heating to 400 °C, we obtained a CNT/PBO composite film. Mechanical property measurements revealed that the CNT/PBO films exhibited a high tensile strength (151 ...

High-Conductivity Solution-Processed Carbon Nanotube Networks as Transparent Electrodes in Organic Solar Cells

ABSTRACTSolutions of individual, unbroken single-walled carbon nanotubes in organic solvent were fabricated in a reductive dissolution process. Transparent conductive films deposited from these organic inks gave a significantly higher conductivity to absorptivity ratio than those cast from an aqueous dispersion of carbon nanotubes. For example, films from the organic ink have achieved a sheet resistance of 250 Ω/□ with transmittance of 92% at 550 nm wavelength, compared to 76% transmittance for a 250 Ω/□ film from the aqueous dispersion. The promise of these films as transparent electrodes has been demonstrated by their incorporation into organic solar cells with power conversion efficiency of 2.3%, comparable to that of solar cells produced using indium tin oxide transparent electrodes.

The stability of suspensions of multiwalled carbon nanotubes in organic solvents in the presence of triton X-165

The stability of suspensions of multiwalled carbon nanotubes in isopropanol, toluene, and p-xylene has been studied. Suspensions of multiwalled carbon nanotubes in isopropanol (unlike those in toluene and p-xylene) display high aggregation stability, which is explained by the formation of repulsive solvation layers as a result of interactions between the polar solvent and nanotube surface. The addition of a nonionic surfactant, Triton X-165, noticeably increases aggregate sizes and accelerates sedimentation processes in nanotube suspensions in isopropanol, while, in toluene and p-xylene, the aggregate sizes decrease and the nanotube suspensions are stabilized.

Using solution thermodynamics to describe the dispersion of rod-like solutes: application to dispersions of carbon nanotubes in organic solvents

We report a simple model describing the solubility of rods in solvents, expressing the final result explicitly in terms of the surface entropy and the enthalpy of mixing. This model can be combined with any expression for the mixing enthalpy depending on the requirements. For example, in one instance it predicts the dispersed concentration of rods to decrease exponentially with the Flory–Huggins parameter of the dispersion. Using a different enthalpy function, it predicts a Gaussian peak when concentration is plotted versus solvent surface energy. The model also suggests specific solvent–rod interactions to be important and shows the dispersed concentration to be very sensitive to ordering at the solvent–rod interface. We have used this model to describe experimental results for the concentration of dispersed nanotubes in various solvents. Qualitative agreement with these predictions is observed experimentally. However, we suggest that the fact that quantitative agreement is not found may be explained by solvent ordering at the nanotube surface.

Functionalization of Single-Walled Carbon Nanotubes with a Redox Active and Acid/Base Responsive TTFV Polymer

A tetrathiafulvalene vinylogue (TTFV) and phenylacetylene based conjugated polymer was designed and synthesized. The polymer backbone can reversibly fold and unfold under the control of redox and acid/base stimuli. This conformational switching property allows the polymer to reversibly disperse and release single-walled carbon nanotubes in organic solvents in a controlled manner, which in turn offers a new non-covalent functionalization method for single-walled carbon nanotube processing.

Dispersion of carbon nanotubes in organic solvents initiated by hydrogen bonding interactions

AbstractPhase transfer of multiwalled carbon nanotubes (MWNTs) from an aqueous phase into an organic phase is achieved. The transfer uses the hydrogen‐bonding interactions between the disaccharide group of a sugar‐based amphiphile and oxygenated functional groups on the surface of MWNTs. The dispersion of carbon nanotubes in a wide range of organic solvents is enabled, which represents the first example of solubilization of carbon nanotubes in organic solvents via hydrogen bonding interactions. © 2012 American Institute of Chemical Engineers AIChE J, 58: 2997–3002, 2012

Reversible dispersion and releasing of single-walled carbon nanotubes by a stimuli-responsive TTFV-phenylacetylene polymer

A TTFV-phenylacetylene folding polymer was synthesized to exhibit the property of reversibly dispersing and releasing single-walled carbon nanotubes in organic solvents under the control of redox or pH stimuli.

High electrical performance of carbon nanotubes/rubber composites with low percolation threshold prepared with a rotation–revolution mixing technique

The present study demonstrates a novel mixing approach for achieving a good dispersion of carbon nanotubes (CNTs) in a styrene–butadiene rubber (SBR), which leads to a significant improvement in electrical properties. Our mixing technique consists of (1) pretreatment by ultrasonication to disentangle the bundles of CNTs in organic solvent and (2) “rotation–revolution” mixing of the CNTs with SBR without mechanical shear, which prevents CNTs from collapsing during the mixing process. The present mixing method does not require the addition of any dispersing agents (amphiphilic molecules) or chemical modification of the CNTs to obtain a good dispersion. Compared with a conventional Banbury mixing technique, our method leads to a significant decrease in the percolation threshold (less than 1 phr), where the electrical conductivity suddenly increases due to the formation of percolation networks of CNTs in SBR. This is because the aspect ratio of the CNTs was maintained even after the mixing process, whereas CNTs were broken during the conventional Banbury mixing. The effect of using different types of CNTs on electrical conductivity was also investigated. The results show that the percolation threshold is largely related to the structural quality (graphitization) of the CNTs as well as their aspect ratio.

Functionalized multiwall carbon nanotubes incorporated polymer/fullerene hybrid photovoltaics

Multiwall carbon nanotubes are introduced into poly(3-hexylthiophene) and [6,6] phenyl C61 butyric acid methyl fullerene, bulk heterojunction organic photovoltaic devices. Utilization of nanotubes requires chemical modifications for compatibility with solution processable photovoltaics. Better dispersions of carbon nanotubes in organic solvents are achieved by acid functionalization of tubes. Pristine and acid treated multiwall carbon nanotubes have been incorporated into the photoactive layer and better results in fill factors of 62% and efficiency of 2.3% are achieved under Air Mass 1.5 Global illumination through the use of acid treated nanotubes.

Hyperbranched Polyethylenes and Functionalized Polymers by Chain Walking Polymerization with Pd‐Diimine Catalysis

AbstractChain walking polymerization (CWP) with Pd‐diimine catalysis represents a novel concept for the synthesis of hyperbranched polyethylenes (HBPEs) and functionalized polymers from ethylene stocks. This article summarizes recent developments in this research area. The properties of HBPEs have recently been studied and their application as lubricant viscosity additives, polymer processing aids, and polymers for the functionalization and solubilization of carbon nanotubes in organic solvents have been explored, with some outstanding features having been discovered. Using the CWP strategy, we have also synthesized a range of functionalized HBPEs covalently tethered with a variety of functional groups, including POSS nanoparticles, ATRP‐initiating sites, methacryloyl and acryloyl double bonds, and backbone‐incorporated functionalized ring units.magnified image

Tailoring Triblock Copolymers for Dispersion of Individual, Pristine, Single-Walled Carbon Nanotubes in Organic Solvents

Triblock copolymers, polyethylene oxide-(hexa-p-phenylene)-polyethylene oxide, were synthesized and used for dispersing single-walled carbon nanotubes (SWNT) in organic solvents. The resulting dispersions comprise mostly of individual tubes, as indicated by transmission electron microscopy at cryogenic temperatures. The dispersions could be dried and redispersed by the addition of a solvent, offering a useful method of application of predispersed SWNT. In situ optical spectroscopy indicates that the block copolymers which self-assemble in the native solution physically adsorb to the SWNT surface via the hexa-p-phenylene moiety. The noncovalent, weak adsorption competes with the polymer self-assembly, as clearly indicated by the emission spectra. The balance between self-assembly and adsorption is sensitive to the length of ethylene oxide side chains. The approach presented here may serve for optimization of the structure and composition of polymeric dispersants where one can chose between a long tail and a long adsorbing moiety, according to the specific needs presented by different applications of SWNT.