CNT Aggregates Research Articles

Mapping carbon nanotube aspect ratio, concentration and spinning in FCCVD synthesis controlled by sulphur

Floating catalyst chemical vapor deposition (FCCVD) enables ultrafast synthesis of CNTs and other 1D nanoparticles and their direct assembly as macroscopic solids. The chalcogen growth promotor in FCCVD produces high aspect ratio CNTs that can aggregate in the gas phase and form an aerogel which can be continuously spun as macroscopic fibres or sheets. We study the role of sulphur in controlling CNT morphology and aggregation by synthesising CNTs under a wide range of S/C ratios (0.001 to 5 wt.%) and determining their diameter and length distributions, number concentration and form of aggregation. Increasing S/C ratio in this range increases mean number of CNT walls from 1 to 8, decreases mean length from 34 to 6 µm, but CNT number concentration remains approximately constant at 8 × 108#/cm3. Assuming growth within the first 3 cm of the reactor, longitudinal growth rate spans 1.5- 6.5 µm/s for the different CNT morphologies, but with similar mass throughput of 700 attogram/catalyst. This indicates the amount of carbon reaching the catalyst and solidifying as CNT remains constant regardless of the sulphur available in the catalyst, suggesting the rate limiting process is not at the catalyst/promoter interface but instead in the transport of carbonaceous active precursors to the catalyst, either due to their diffusion in the gas phase or decomposition kinetics. The CNTs produced range from polymer-like, which readily bundle and form aerogels, to rod-like that do not. We include aerogelation “phase diagrams” for different CNT concentrations, aspect ratios and CNT bending stiffness.

The Effect of Heat Treatment on Wear Properties of Ni-B-CNT Electroless Coating with Different Carbon Nanotube Concentration on AISI 4340 Steel

Study wear resistance for heat treatment of Ni-B-CNT electroless coatings. Different concentrations for CNT (0 ,0.35 and 0.7 g/l Ni-B-CNT composite coatings deposition on 4340 steel. After the procedure of coating, all samples were heat treatment. The test wear of a coating was valued with pin on disk technique. Preparation of Ni–B–CNT electroless coatings are with using nickel chloride in alkaline bath, borohydride and Multi walled carbon nanotubes. characterization with FESEM, micro hardness, XRD and surface roughness. Study for surfaces of worn with EDS and FESEM. Micro hardness results are show that the larger hardness1010 HV is gained by heat treatment for coating (Ni-B- 0.35 g/L CNT) because of concentration CNT caused structure conversion for coating Ni-B from amorphous to crystalline. Also, CNT prevent maximum heat production and decrease of the friction coefficient during test wear. CNT aggregation was noted result the presence for more particles (Ni-B - 0.7g/l CNT) that occur create roughness and also lead to increase in rate of wear because of big particles with weakly joined in matrix of Ni.

Three-stage channel sprays carbon nanotubes onto carbon fibers surface, preparing high performance carbon fibers composites

Carbon fibers composites performance strengthening through graft Carbon nanotubes is a research hotspot at present. Here, a method for rapidly and effectively dispersing and removing CNT aggregates during spraying the CNTs onto CFs surface by the three-stage channel is reported. The scanning electron microscopy image characterization results shows that the three-stage channel has a significant effect on the removal of CNTs aggregates, and the obtained p-CNTs has a good dispersion morphology. Under the same condition, p-CNTs@CFs/EP and CNTs@CFs/EP composites are prepared by the three-stage channel spraying and direct spraying method respectively. Compared with no treatment CFs composites (o@CFs/EP), the tensile, compressive and interlaminar shear strength and radial thermal conductivity (λ⊥) of the CNTs@CFs/EP are increased by 7%, 11%, 9% and 80% (2452.04 MPa, 1209.37 MPa, 89.30 MPa and 1.28 W/(m·K)), the p-CNTs@CFs/EP increased by 29%, 35%, 37% and 203% (2949.06 MPa, 1471.67 MPa, 112.37 MPa and 2.15 W/(m·K)), the CNTs@CFs/EP resistivity is 72.72 Ω·m, a 64% decrease, the p-CNTs@CFs/EP is 45.45 Ω·m, a decrease of 78%. This indicates that the CFs composites prepared by the three-stage channel spraying method has better performance than direct spraying and no treatment. This method provides a new idea for CFs composites performance strengthening.

Fluorinated carbon nanotubes as nonvolatile additive to the active layer of polymer/fullerene solar cells

Highly dispersed fluorinated SWCNTs of submicron length were prepared, characterized and tested as nonvolatile additive to the active layer of polymer/fullerene organic solar cells. Two types of initial SWCNT materials – TUBALL® (OCSiAl) and Super purified plasma tubes (Nanointegris Inc.) – were used. The absence of big CNT aggregates was revealed by atomic force microscopy. The absence of metallic SWCNTs is confirmed by optical spectra of fluorinated SWCNT dispersions. Reproducible increase of the main performance parameters of solar cells (short circuit current, open circuit voltage, fill factor and power conversion efficiency) was obtained upon admixing a small amount of fluorinated SWCNTs (less than 1% weight) into the polymer/fullerene active layer, with either P3HT or PCDTBT donor and either PC60BM or PC70BM acceptor for both direct and inverted device architectures. Since effective charge mobility did not change upon fluorinated SWCNT admixture, the improvement of solar cell performance is not related to SWCNT-induced modification of the electronic structure of the active layer components or charge transfer via fluorinated SWCNTs. Presumably, the origin of this improvements is geometric optimization of the active layer morphology (improving connectivity of donor and acceptor domains) by fluorinated SWCNTs due to their high aspect ratio.

Robust Core–Shell Carbon-Coated Silicon-Based Composite Anode with Electrically Interconnected Spherical Framework for Lithium-Ion Battery

Carbon-coated Si/carbon nanotube/graphene oxide (C-Si/CNT/GO) microspheres with a robust core–shell composite structure were successfully fabricated by efficient and scalable spray-drying and chemical vapor deposition (CVD) for application as a lithium-ion battery (LIB) anode. The amphiphilic GO nanoparticles facilitated the uniform dispersion of Si nanoparticles by suppressing the CNT aggregation in the Si/CNT/GO microspheres, efficiently forming a robust Si/CNT/GO microsphere composite structure. The surface of the Si/CNT/GO microsphere composite was coated with carbon using CH4 via CVD to enhance its cycling performance. The four building block components, namely, Si nanoparticles, CNTs, and GO nanoparticles as the core and the carbon-coating layers as the shell, provided high electrochemical capacity, excellent electrical conductivity, efficient buffer space for the volume expansion of the Si nanoparticles, and high structural stability during lithiation/delithiation. The C-Si/CNT/GO composite anode also exhibited excellent electrochemical performance with high specific capacity (2921 mAh g–1 at 100 mA g–1), long cycle life (1542 mAh g–1 at 200 mA g–1 after 100 cycles), and high charge/discharge rate (1506 mAh g–1 at 6 A g–1). This approach for fabricating core–shell structured Si-based composite anodes with excellent electrochemical performance will provide a significant breakthrough for developing next-generation LIBs.

Evanescent waves attenuation and stiffness enhancement of viscoelastic locally resonant metamaterials by nanofiller addition- a multi-scale k(ω) based modeling

A CNT-modified viscoelastic locally resonant metamaterial (LRM) is investigated to study the complex dispersion curve, loss factor, wave transmission spectra, and effective stiffness. The dispersion curve analysis is based on the Bloch theorem applied to the nanocomposite LRM (NLRM) equations of motion and solving the resulting eigenvalue problem by the finite element method. The transmission spectra is obtained by COMSOL Multiphysics software. Due to the material viscoelasticity, multi-scale frequency-dependent homogenization of the nanocomposite is performed within the k(ω) framework which is systematically presented. The CNTs are added to the host LRM to enhance its stiffness without a significant increase in density. Hence, the impedance mismatch between the host nanocomposite and the coated cores is increased which affects the complex branch of NLRM, and shifts the imaginary part of the wave number to greater values without considerable change in its real part. So, the NLRM loss factor is increased which leads to lower wave transmission. Therefore, the NLRM exhibits simultaneously higher stiffness and loss factor with respect to ordinary LRMs. The effective stiffness of the CNT/host nanocomposite and the complex LRM dispersion curve and attenuation diagram are validated by experimental and numerical results, respectively. A parametric study is conducted to consider the effects of the CNT volume fraction (CNTVF), aspect ratio (AR), aggregation state and the CNT/host interface properties. Results show that the CNTVF and AR have the most influential effects on the NLRM properties. The CNT aggregation state is detrimental to the NLRM stiffness and wave attenuation properties too.

Effective addition of nanoclay in enhancement of mechanical and electromechanical properties of SWCNT reinforced epoxy: Strain sensing and crack-induced piezoresistivity

Many studies were performed to improve CNT dispersion into epoxy using different mechanical dispersion methods as well as CNT functionalization. In this study, a novel method is introduced to enhance CNT dispersion using 2D nanoclay as a secondary filler. Hence, this study was aimed to investigate the effect of nanoclay platelets on electrical, mechanical, and piezoresistive characteristics of the SWCNTs doped epoxy nanocomposites. Two different types of nanocomposites were prepared for comparison including binary (SWCNT/epoxy) and hybrid (SWCNT-nanoclay/epoxy) states. CNT content of 0.1 wt% was used for the binary and hybrid states while two different nanoclay loadings (0.5 wt% and 1.0 wt%) were employed in the hybrid nanocomposites. Tensile and mode I fracture tests were performed for the mechanical and electromechanical characterization using two probe techniques while electron microscopy and X-ray diffraction were used for microstructural analysis. Results showed severe CNT agglomeration in the binary state whilst a homogenous CNT dispersion was achieved in the ternary states. The binary nanocomposite showed weak performance in terms of electrical, mechanical and piezoresistive properties caused by severe CNT aggregates. On the other hand, addition of nanoclay into CNTs doped epoxy manifested a significant increase in the electrical, mechanical and piezoresistive-sensitivity performance of the hybrid nanocomposites compared to the binary one. The best performance was achieved at 0.5 wt% nanoclay loading where electrical conductivity increased by six orders of magnitude, UTS increased by 37%, KIC and GIC increased by 34% and 64%, respectively, with respect to the binary nanocomposite. Crack-pinning and crack deflection were accounted for the fracture toughness increase in ternary composites. Nonlinear piezoresistivity resulting from the predominate effect of tunneling resistance ruled piezoresistivity in the hybrid nanocomposites. A sensitivity of 2.1 and 2.0 at strain of 0.01 were obtained for 0.5 wt% and 1.0 wt% nanoclay contents, respectively, whereas no sensitivity was achieved for the binary composite.

Predicting the strength of carbon nanotube reinforced polymers using stochastic bottom-up modeling

It is intended to predict the strength of carbon nanotube reinforced polymer. For this purpose, a sequential multi-scale modeling technique is developed taking into account effective parameters at various scales of micro, meso and macro. CNT-polymer interaction, CNT orientation and CNT waviness are considered at the scale of micro, while formation of CNT aggregates is captured at meso-scale. The occurrence of failure in the form of either matrix failure or CNT and polymer debonding is considered in the modeling as the two prominent failure mechanisms under tensile loading. At the uppermost scale of macro, the investigated material region is partitioned into constitutive blocks using regular tessellation technique accounting for inhomogeneous material behavior. The induced uncertainties during the processing of carbon nanotube reinforced polymers necessitate stochastic modeling. The experienced inconsistencies consisting of CNT length, orientation, waviness pattern and intensity of agglomeration are captured using random parameters. Therefore, the constitutive behavior of each block at macro-scale is randomly picked from the outputs of the conducted modeling at lower scales and full stochastic modeling is implemented. The outputs of the developed modeling are compared with available experimental observations in published data and remarkable agreement is observed.

Influence of polymer type and carbon nanotube properties on carbon nanotube/polymer nanocomposite biodegradation

The interaction of anaerobic microorganisms with carbon nanotube/polymer nanocomposites (CNT/PNC) will play a major role in determining their persistence and environmental fate at the end of consumer use when these nano-enabled materials enter landfills and encounter wastewater. Motivated by the need to understand how different parameters (i.e., polymer type, microbial phenotype, CNT characteristics) influence CNT/PNC biodegradation rates, we have used volumetric biogas measurements and kinetic modeling to study biodegradation as a function of polymer type and CNT properties. In one set of experiments, oxidized multiwall carbon nanotubes (O-MWCNTs) with a range of CNT loadings 0–5% w/w were incorporated into poly-ε-caprolactone (PCL) and polyhydroxyalkanoates (PHA) matrices and subjected to biodegradation by an anaerobic microbial community. For each CNT/PNC, complete polymer biodegradation was ultimately observed, although the rate of biodegradation was inhibited above certain critical CNT loadings dependent upon the polymer type. Higher loadings of pristine MWCNTs were needed to decrease the rate of polymer biodegradation compared to O-MWCNTs, an effect ascribed principally to differences in CNT dispersion within the polymer matrices. Above certain CNT loadings, a CNT mat of similar shape to the initial PNC was formed after polymer biodegradation, while below this threshold, CNT aggregates fragmented in the media. In situations where biodegradation was rapid, methanogen growth was disproportionately inhibited compared to the overall microbial community. Analysis of the results obtained from this study indicates that the inhibitory effect of CNTs on polymer biodegradation rate is greatest under conditions (i.e., polymer type, microbial phenotype, CNT dispersion) where biodegradation of the neat polymer is slowest. This new insight provides a means to predict the environmental fate, persistence, and transformations of CNT-enabled polymer materials.

Enhanced Thermal Conductivity of Carboxyl (–COOH) Functionalized Multi-Walled Carbon Nanotube (MWCNT)-Silicone Oil Based Nanofluids

Thermal conductivity and viscosity studies of carboxyl (–COOH) functionalized multi-walled carbon nanotubes-Silicone oil nanofluids were discussed in this work. Carboxyl (–COOH) functionalized MWCNT-Silicone oil nanofluids were prepared in various concentration ranges from 0.001 to 0.005 g of COOH-MWCNT and characterized at a range of temperatures between 303 K to 323 K. The thermal conductivity of carboxyl (–COOH) functionalized MWCNT-Silicone oil nanofluids increases with the raise in concentration of MWCNTs and also with the raise in temperatures. Mechanism for the enhancement of Silicone oil with concentration of MWCNT is due to the percolation of heat through the nanotubes through axial direction than through radial direction. Because of large aspect ratio of nanotubes heat transfer inside MWCNTs is also more. Also, as the temperature increases the viscosity of the (–COOH) functionalized MWCNT-Silicone oil nanofluids decreases, because CNT aggregation kinetics may contribute resulting in enhanced thermal conductivity.

Electrically conductive polyacrylamide/carbon nanotube hydrogel: reinforcing effect from cellulose nanofibers

The development of polymeric hydrogels with new functionalities is becoming an aspiration in various fields. Here we report a simple method to fabricate a conductive polyacrylamide (PAM)-based hydrogel by the incorporation of carbon nanorubes (CNTs). However, the major challenge for these hydrogels is CNT aggregation in PAM, which decreases both mechanical and electrical properties of the composite hydrogels. Inclusion of cellulose nanofibers (CNFs), is expected to disperse the CNTs well, thereby reinforcing the PAM hydrogels. Hence, by mixing the CNFs and CNTs in the AM hybrid solutions, a PAM/CNF/CNT composite hydrogel is prepared through in situ polymerization. Specifically, with incorporation of 1 wt% CNF and 1 wt% CNT into PAM, the PAM/CNF/CNT-1 hydrogel, with an electrical conductivity of 8.5 × 10−4 S/cm, shows a threefold higher fracture tensile strength than the pure PAM hydrogel. Given the improved mechanical properties and electrical conductivity, the use of CNF as a reinforcing agent for both PAM and CNT provide a versatile method to fabricate conductive hydrogels, and has potential to expand their application in the field of bio-medical engineering and electrical devices.

The effect of external applied fields on the third order nonlinear susceptibility and two-photon absorption cross-section of E5CN7@Fe3O4-CNT

The third order nonlinear optical properties and two-photon absorption(TPA) cross-section of nematic liquid crystals (NLCs) (E5CN7) doped with Fe3O4 nanoparticles, single wall carbon nanotubes (SWCNTs) and Fe3O4-CNTs were investigated at 632.8 nm. For this aim, the low power single beam was used in Z-scan technique. The study was performed with two different concentrations of dopant with and without the electric field (15 Volt) and magnetic field (0.5 Tesla). The functionalization of SWCNTs with Fe3O4 diminishes the CNT aggregation while the third order nonlinear susceptibility and TPA cross-section are increased. The results show that the best concentration and dopant in E5CN7 without any applying fields is 1% Fe3O4-CNT. After applying electric and magnetic fields and compare the results, the E5CN7@1% Fe3O4-CNT under electric field exhibits the largest nonlinear responses among all the samples. The direction of external fields with respect to the director axisn→ and then the type of initial alignment are crucial factors for changing the nonlinearity parameters. Furthermore, these results show that E5CN7@1% Fe3O4-CNT may be the promising candidate for the magneto-optical devices.

CNT-volume-fraction-dependent aggregation and waviness considerations in viscoelasticity-induced damping characterization of percolated-CNT reinforced nanocomposites

Elastic and viscoelastic-damping behaviors of multi-walled carbon nanotube (MWCNT) reinforced polymer matrix nanocomposites are investigated by the HFGMC micromechanical method. Utilizing the elastic-viscoelastic correspondence principle, the frequency dependent properties are derived analytically from the time dependent creep curve. The CNT displays transversely isotropic directional behavior, however, the polymer matrix and the interphase representing the CNT/polymer interactions, obey a viscoelastic constitutive law. The CNT percolation, random orientation and random arrangement within the matrix are considered. After validating the proposed micromechanical model by experimental results, the parametric studies, including the effects of the CNT aggregation, waviness and percolation states, the loading frequency, and the interphase features on the nanocomposite effective elastic modulus, creep compliance, storage modulus, loss modulus and hysteresis loop are conducted. It is found that considering the CNTVF-dependent aggregation state gives a threshold value of the CNTVF leading to improve the nanocomposite effective properties. Also, as the CNT wave amplitude increases, the effective properties are degenerated more. However, it includes a minor effect for the CNTVFs less than 0.3%. The CNT percolation threshold increases by increasing the aggregation level and the interphase thickness, too.

Effect of Height on CNT Aggregates Size and Shape in Freeboard Region of a Fluidized Bed

Effect of Height on CNT Aggregates Size and Shape in Freeboard Region of a Fluidized Bed

Synergistic effect of non-covalent interaction in colloidal nematic liquid crystal doped with magnetic functionalized single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs), CNT@Fe3O4, and Fe3O4 nanocomposites were doped to eutectic uniaxial nematic liquid crystal (NLC's) (E5CN7) to improve physiochemical properties such as phase transition temperature, activation energy (Ea), dielectric anisotropy, and electro-optical properties. The thermal study of nematic phase shows a decrease in the nematic to isotropic phase transition temperature as CNT is doped. However, higher doping concentration of CNTs leads to the further increase in transition temperature. The anchoring effect or π-π interaction plays a key role in N-I phase transition. The functionalization of SWCNTs with Fe3O4 diminishes the CNT aggregation while the magnetic susceptibility is increased. The functionalized CNT doping to NLC's decrease significantly the phase transition temperature compared to doping of non-functionalized CNTs. Attractive interaction between guest and host molecules by magnetic and geometry effect increased the enthalpy and entropy of phase transition in the SWCNT@Fe3O4 sample compared to non-functionalized CNT doped system. Also, the Ea values are decreased as SWCNT@Fe3O4 is doped to pure E5CN7. The difference of N-I phase transition temperature was observed in Fe3O4 and CNT@Fe3O4 compared to SWCNT doped systems. Finally, dielectric anisotropy was increased in the doped system compared to pure NLC.

The microstructure and mechanical properties of 3D printed carbon nanotube‐polylactic acid composites

This article reports 3D printing of carbon nanotube‐polylactic acid (CNT‐PLA) composites using an extrusion‐based Fused Deposition Modeling (FDM) method. CNTs with an average diameter of 128 nm and an average length of 2.5 μm were first compounded with PLA and extruded into feedstock filaments at 0.5%, 2.5%, and 5% (w/w) CNT loadings. CNT aggregates were observed, but no clogging occurred during printing with a 500‐μm print nozzle. The rheology of the CNT‐PLA samples was characterized to understand the printing‐induced alignment of CNTs along the road axis. Additionally, the effect of printing flow rate was explored for a fixed printing gap and nozzle diameter. Higher flow rates reduced the void fraction in the FDM parts, but unexpectedly resulted in less degree of CNT alignment, which is attributed to radial flow and fusion between adjacent roads. The mechanical properties of the CNT‐PLA tensile test coupons were characterized. Inclusion of CNTs increased the Young's modulus by 30% at 5% CNT loading, but reduced the tensile strength and overall toughness of the FDM parts. Experimental data were compared against the Rule of Mixtures (RoM) model, the Halpin‐Tsai model, and the modified RoM model and were further explained by the void fraction and CNT orientation. POLYM. COMPOS., 39:E1060–E1071, 2018. © 2017 Society of Plastics Engineers

Interface optimization of CNT/Cu composite by forming TiC nanoprecipitation and low interface energy structure via spark plasma sintering

CNT/Cu composite was fabricated by using copper powders within small amounts of titanium nanometer powder via balling milling and followed by spark plasma sintering. Microstructure analysis by SEM, FETEM and EDS shows that laminar grain shape of the composite is inherited from the starting flake powder, and some CNT aggregates are observed at the edge of copper grains. TiC nanoprecipitation, as a transition phase from CNT to metal matrix, is formed in the composites; this phase shows a typical orientation relationship with the Cu matrix, that is Cu (002)//TiC (002). The coherent relationship between TiC and Cu grain reveals the formation mechanism of titanium carbide. Besides, TiC nanostructures contribute to the load transfer of the interface and then the enhancement of the mechanical strength. Furthermore, low angle grain boundary is also revealed by deflecting Moiré fringes. It improves the dislocation carrying capacity of the interface.

Adsorption mechanism of different organic chemicals on fluorinated carbon nanotubes

Multi-walled carbon nanotubes (MC) were fluorinated by a solid-phase reaction method using polytetrafluoroethylene (PTFE). The surface alteration of carbon nanotubes after fluorination (MC-F) was confirmed based on surface elemental analysis, TEM and SEM. The incorporation of F on MC surface was discussed as F incorporation on carbon defects, replacement of carboxyl groups, as well as surface coating of PTFE. The adsorption performance and mechanisms of MC-F for five kinds of representative organic compounds: sulfamethoxazole (SMX), ofloxacin (OFL), norfloxacin (NOR), bisphenol a (BPA) and phenanthrene (PHE) were investigated. Although BET-N2 surface area of the investigated CNTs decreased after fluorination, the adsorption of all five chemicals increased. Because of the glassification of MC-F surface coating during BET-N2 surface area measurement, the accessible surface area of MC-F was underestimated. Desorption hysteresis was generally observed in all the sorption systems in this study, and the desorption hysteresis of MC-F were stronger than the pristine CNTs. The enhanced adsorption of MC-F may be attributed the pores generated on the coated PTFE and the dispersed CNT aggregates due to the increased electrostatic repulsion after fluorination. The rearrangement of the bundles or diffusion of the adsorbates in MC-F inner pores were the likely reason for the strong desorption hysteresis of MC-F. The butterfly structure of BPA resulted in its high sorption and strong desorption hysteresis. The exothermic sorption character of OFL on CNTs resulted in its strong desorption hysteresis.

Impact behavior of CNT-filled PP/EPDM blends: effect of dynamic vulcanization and PP-g-MA compatibilizer

The impact strength and crystallite structure of un-vulcanized and dynamically vulcanized polypropylene/ethylene-propylene terpolymer (PP/EPDM) blends and polypropylene/ethylene-propylene terpolymer/carbon nanotube (PP/EPDM/CNT) blend nanocomposites with and without maleic anhydride-grafted polypropylene (PP-g-MA) were studied. The results showed that incorporation of EPDM increased the impact toughness of PP matrix by promoting debonding and cavitation of rubber particles. Dynamic vulcanization increased the interfacial adhesion leading to superior impact strength. Incorporation of CNT into PP/EPDM blends changed the crystallization behavior of the PP matrix and further increased the impact resistance. Morphological observations on impact-fractured surfaces indicated that dominant failure modes of CNTs in blend nanocomposites with and without PP-g-MA are pulling out and breakage of nanotubes, respectively. While the PP-g-MA had a negative effect on the impact strength of PP, the results demonstrated that its presence enhanced the impact strength of the blends and blend nanocomposites mostly via enhancing the adhesion between the PP and EPDM particles and improving the dispersion of CNTs in the matrix, respectively. The former decreases the rubber particle size and the latter decreases the size of CNT aggregates and crystallites.

Aggregates of single-walled carbon nanotube bundles in a surfactant solution

We have carried out small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and 1H NMR studies as a function of temperature on 0.1wt.% single-walled carbon nanotubes (SWCNTs) dispersed aqueous (D2O) cetyl trimethylammonium bromide (CTAB) solution. We find that the single-walled carbon nanotubes in this system aggregate to form bundles and depending on the temperature of the system, the bundles aggregate and exhibit four different structures namely, Y-shaped structures, net-like structures, domains of small spherical structures and sheet-like structures. Our DSC thermogram also showed peaks at these structural transition temperatures of the CNT aggregates. Our SEM and 1H NMR studies reveal that the CTAB micelles are adsorbed on the CNT aggregates and the adsorption depends on the temperature and structure of the CNT aggregates.