Phase behavior and structure formation for diblock copolymers composed of side-chain liquid crystalline and glassy amorphous components

Phase behavior and structure formation in liquid crystallization of a side-chain liquid crystalline (LC) block copolymers composed of poly[11-(4′-cyanophenyl-4″-phenoxy)undecyl acrylate] (PA₁₁OCB) and polystyrene (PSt) were investigated by using a time-resolved small-angle X-ray scattering technique (SAXS), differential scanning calorimetry and polarizing optical microscopy. PA₁₁OCB homopolymer formed smectic (Sm) liquid crystal. Liquid crystallization behavior of the block copolymers depended on the molecular weight and the block composition. When molecular weight was relatively low, order-disorder transition (ODT) was observed. In cooling of such block copolymers, liquid crystallization seemed to wait for the formation of LC-rich microphase by ODT. For the block copolymers with relatively high molecular weight, liquid crystallization slightly enlarged the domain spacing without changing the microphase separation structure in the melt. The order of the LC phase was lowered with decreasing dimensionality of the LC microdomains, that is, the LC blocks formed smectic liquid crystal in the matrix or lamellar microphase while liquid crystallization in the cylindrical microdomains did not show smectic but maybe nematic liquid crystal. Moreover, the LC blocks within the spherical microdomains did not liquid crystallize. From the 2-D SAXS with applying shear flow, the Sm layers were orientated perpendicularly to the interface of the microphase separation. The relation between the layer thickness of the LC phase and the molecular weight suggested that the main chain was extended normally to the interface of the microphase separation.     

Nebulization of single-walled carbon nanotubes for respiratory toxicity studies

An ultrafine aerosol consisting of airborne single-walled carbon nanotubes (SWCNTs) was produced by nebulizing functionalized SWCNTs in methanol. Prior to atomization, purified SWCNTs were functionalized with aryl sulfonate groups via a Birch reaction. The functionalized SWCNTs were then dispersed in methanol and nebulized using a TSI-3076 constant output atomizer. Atomic force microscopy of a mica plate placed in the flow revealed both individual and bundled SWCNTs. We anticipate that this method for producing ultrafine mists of SWCNTs will enable respiratory toxicity studies of inhaled ultrafine SWCNT particulate.     

One-dimensional silver nanostructures on single-wall carbon nanotubes

We report the synthesis and characterization of one-dimensional silver nanostructures using single-wall carbon nanotubes (SWCNT) as a template material. Transmission electron microscopy and scanning tunneling microscopy are consistent with the formation of a one-dimensional array of silver particles on SWCNT. We observe evidence for the excitation of the longitudinal silver plasmon mode in the optical absorption spectra of Ag-SWCNT dispersions, even in the lowest silver concentrations employed. The results indicate that silver deposits on SWCNT may be candidates for light-to-energy conversion through the coupling of the electric field excited in arrays of plasmonic particles.     

Controlled oxygen plasma treatment of single-walled carbon nanotube films improves osteoblastic cells attachment and enhances their proliferation

The effects of oxidative treatment of single-walled carbon nanotubes (SWCNTs) on the adhesion and proliferation of human osteoblasts (SAOS-2) were investigated. The surface properties of SWCNTs after oxygen plasma treatment were characterized by contact angle measurement, scanning electron microscopy and Raman spectroscopy. The immunofluorescent staining of vinculin, actin filaments and nuclei was used to probe cell adhesion and growth on SWCNT films. Our results show that adhesion and proliferation of human osteoblasts cultivated on SWCNT films indeed depends on the degree of an oxidative treatment. As an optimal procedure was found the treatment with oxygen plasma for 5 min. In the latter case the osteoblasts form a confluent layer with pronounced focal adhesions throughout the entire cell body. The optimal conditions compromise the effect of hydrophilic character of SWCNT films and the level of damage of SWCNT surface.     

The influence of different shaped nanofillers (1D, 2D) on barrier and mechanical properties of polymer hybrid nanocomposites based on PET prepared by in situ polymerization

In this report, we investigated how barrier and mechanical properties of poly(ethylene terephthalate) were influenced by carbon nanoadditives which differ in shape (1D, 2D) and particle size. The results obtained for PET/expanded graphite (EG) and PET/single‐walled carbon nanotubes (SWCNT) were compared with the results obtained for PET/EG+SWCNT hybrid nanocomposites. The different morphologies affect the dispersion of carbon nanoparticles in in situ prepared PET nanocomposites and play a crucial role in structure–property relationship. Good distribution of expanded graphite nanosheets along with some nanotube agglomerates was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Uniformly distributed EG with SWCNT agglomerates caused an enhancement in mechanical properties. We also found that the barrier properties of PET/EG+SWCNT hybrid nanocomposites are far better than neat PET. The described influence of carbon nanomaterials on the properties of PET hybrid nanocomposites is mostly due to addition of well‐exfoliated graphene nanoplatelets and less due to the presence of tubular carbon nanoparticles, which were observed to form agglomerates. POLYM. COMPOS., 37:1949–1959, 2016. © 2015 Society of Plastics Engineers     

Growth of Cement Hydration Products on Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNT) were distributed on the surface of ordinary Portland cement (OPC) grains. The OPC/SWCNT composite was then hydrated at a 0.5 w/c ratio. The effects of the SWCNT on the early hydration process were studied using isothermal conduction calorimetry, high-resolution scanning electron microscopy and thermogravimetric analysis. The observed behavior of the composite samples was compared with both OPC sonicated without SWCNT and previously published data on as-delivered OPC. The SWCNT were found to accelerate the hydration reaction of the C₃S in the OPC. The morphology of both the initial C₃A and the C₃S hydration products were found to be affected by the presence of the SWCNT. In particular, the nanotubes appeared to act as nucleating sites for the C₃S hydration products, with the nanotubes becoming rapidly coated with C–S–H. The resulting structures remained on the surface of the cement grains while those in the sonicated and as-delivered OPC samples grew out from the grain surfaces to form typical C–S–H clusters. Classical evidence of reinforcing behavior, in the form of fiber pullout of the SWCNT bundles, was observed by 24 h of hydration.     

Characterization of SWCNT and PAN/SWCNT films

Three different films, poly(acrylonitrile-co-methylacrylate)/single wall carbon nanotubes (PAN-MA/SWCNT), poly(acrylonitrile-co-methylacrylate)/carbon black (PAN-MA/CB) and pure functionalized SWCNT, are analyzed. The diffuse reflectance and transmittance of the films from 2 μm to 18 μm are characterized with an integrating-sphere Fourier transform spectrophotometer system. The SWCNT film shows high reflectance and low emissivity. Surface roughness characterization by laser scanning confocal microscopy confirms that the low emissivity is not due to a highly polished surface and is therefore more likely due to the metallic behavior of the SWCNTs. Characterization using infra red thermography highlighted the thermal protective behavior of the SWCNT film; the maximum temperature obtained from a 5.2 kW/m² heat flux exposure was 50 °C lower than that for the two (SWCNT, CB) PAN-MA based films.     

Design of carbon nanotube-polymer frameworks by electropolymerization of SWCNT-pyrrole derivatives

Single-walled carbon nanotubes (SWCNTs) have been functionalized by electropolymerizable pyrrole groups following covalent and non-covalent strategies. The covalent pyrrole grafting was carried out by ester formation between pyrrole alcohol and chemically oxidized SWCNT. The strong π-interactions between pyrene and SWCNT were exploited for the non-covalent adsorption of a new pyrene-pyrrole derivative on the pristine nanotube surface. The pyrrole-ester-SWCNT was solubilized in THF and electropolymerized by controlled potential electrolysis at 0.95 V. The pyrene-pyrrole SWCNT was spread on an electrode surface and electropolymerized in its adsorbed state at 0.95 V in CH₃CN. The reinforced nanostructured polypyrrole SWCNT-framework was investigated with scanning electron microscopy.     

Purification of single-walled carbon nanotubes using a fixed bed reactor packed with zirconia beads

Single-walled carbon nanotube (SWCNT) soot produced by arc discharge was purified through gas and liquid phase oxidations. In the gas-phase oxidation, zirconia beads with different diameters of 1, 5, and 10 mm were packed together with raw SWCNT soot inside a vertical quartz tube to enhance air flow uniformity and an exposed surface area of the raw soot during thermal oxidation in air. A decrease of the bead sizes led to such a stronger oxidation of carbonaceous impurities that ∼10 wt.% higher weight loss was then achieved with the 1 mm beads than without them. A subsequent HNO₃ treatment and the second thermal oxidation were engaged to improve further the purity of SWCNTs. Thermogravimetric (TG) analysis, scanning electron microscopy, high resolution transmission electron microscopy, and Raman spectroscopy were used to characterize the samples. The derivative TG (DTG) curves were deconvoluted to quantitatively determine the SWCNT purity of the samples. Our final purified samples showed a yield of ∼26%, a metal impurity of ∼7% and a SWCNT purity of ∼83% as calculated from the deconvoluted DTG curves.     

Electrical conductivity and transparency of polymer hybrid nanocomposites based on poly(trimethylene terephthalate) containing single walled carbon nanotubes and expanded graphite

Single‐walled carbon nanotubes (SWCNT)/expanded graphite (EG)/poly(trimethylene terephthalate) (PTT) hybrid nanocomposites were prepared via in situ polymerization. Raman spectroscopy and scanning electron microscopy (SEM) were employed to determine both, purity and morphology of the nanofillers and the dispersion of nanotubes and nanosheets. The electrical and optical properties of thin polymer films based on both “single” nanocomposites and hybrid nanocomposites were studied. For PTT/SWCNT nanocomposites, results confirmed that films optical transmittance decreases as the concentration of SWCNT increases, attaining almost no optical transmittance for 0.3 wt % of nanofiller. Conversely, the electrical conductivity of nanocomposites was found to increase by increasing the nanofiller amount and the σ_dc values indicate that percolation occurs at a very low SWCNT content (around 0.05 wt %). In the case of PTT/SWCNT + EG nanocomposites, when the content of SWCNT is 0.05%, the hybrid system presents lower conductivity than that corresponding to the “single” nanocomposite. The incorporation of additional EG to the PTT/SWCNT nanocomposite has a small effect on the electrical conductivity but inhibits the transparency of the system. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44370.     

Synthesis,characterization, and photophysical properties of covalent-linked ferrocene–porphyrin–single-walled carbon nanotube triad hybrid

The ferrocene–porphyrin–single-walled carbon nanotube (Fc–H₂P–SWCNT) triad hybrid was prepared by amidation reaction between carboxylated SWCNT and aminoporphyrin bearing an appended ferrocenyl substituent. The hybrid described here was fully characterized by a combination of analytical techniques such as Fourier transform infrared spectroscopy, Raman, absorption and emission spectroscopy, atomic force and scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The steady emission characteristics revealed the existence of the effective photoinduced electron transfer among ferrocene, excited porphyrin moiety and SWCNT, which was further confirmed by the results of time-resolved transient absorption spectra. The final lifetime of charge-separation state was observed to be 62.9 μs in N,N-dimethylformamide, which was significant increased compared to the reference nanohybrid porphyrin–SWCNT and the reported ferrocene–porphyrin–fullerene triad. Therefore, Fc–H₂P–SWCNT triad hybrid constructed by amidation is rationally expected to be an improved photon-to-electron conversion system.     

The synthesis of covalent bonded single‐walled carbon nanotube/polyvinylimidazole composites by in situ polymerization and their physical characterization

Single‐walled carbon nanotube (SWCNT) polyvinylimidazole (PVI) composites have been prepared by in situ emulsion polymerization. Dispersion of raw SWCNTs in the PVI matrix was improved by surface modification of the SWCNTs using nitric acid treatment and air oxidation. The carbonyl‐terminated SWCNTs were covalently bonded to PVI by in situ polymerization and the SWCNT/PVI composite was thus obtained. The morphological and structural characterizations of the surface‐functionalized SWCNTs and SWCNT/PVI composites were carried out by Fourier transform infrared spectroscopy, X‐ray diffraction, conductivity measurements, scanning, and transmission electron microscopy. Thermograms of the materials were determined by the differential scanning calorimetry technique. The characterization results indicate that PVI was covalently bonded to SWCNTs and a new material was then obtained. The functionalized SWCNTs showed homogenous dispersion in the composites, whereas purified SWCNT resulted in poor dispersion and nanotube agglomeration. SWCNT/PVI composites exhibited chemical stability enhancement in many common solvents. I–V curves of the samples exhibit an ohmic character. Conductivity values for pure SWCNTs, pure PVI and SWCNT/PVI composite were measured to be 3.47, 2.11 × 10⁻⁹, and 2.3 × 10⁻³ S/m, respectively. Because of resonance, a large dielectric constant is obtained for SWCNT/PVI composite, which is not observed for ordinary materials. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Poly(vinyl chloride)/single wall carbon nanotubes composites: Investigation of mechanical and thermal characteristics

Composites of polyvinylchloride (PVC) with single wall carbon nanotubes (SWCNTs) were prepared by plastisol curing. Scanning electron microscopy (SEM) observations revealed that appropriate dispersion of the nanotubes was achieved. The mechanical properties showed that SWCNT improved the Young's modulus and tensile strength of the PVC. The composites have higher elongation at break and toughness as well. By comparing the mechanical properties of the composites, it is found that there is a critical SWCNT loading (about 1 wt%) below which the tensile properties increase with increasing nanofiller concentration. For the composites containing 0.25–0.75 wt% of SWCNT, this situation was observed, whereas for a sample with 1 wt% SWCNT, the mechanical properties decreased due to the agglomeration of the nanotubes. Thermogravimetric analysis indicated that the SWCNT increased T_5%, T_10%, T_50%, T_onset, and T_max and decreased weight loss in the degradation process of the PVC. In addition, by adding SWCNT to the polymer, residual mass at 600°C increased significantly. These results are advantages for the applications of the polymer in which high mechanical properties, including high tensile modulus and toughness, and good thermal properties are needed. J. VINYL ADDIT. TECHNOL., 22:128–133, 2016. © 2014 Society of Plastics Engineers     

Optical absorption response of chemically modified single-walled carbon nanotubes upon ultracentrifugation in various dispersants

Arc discharge single-walled carbon nanotubes (SWCNTs) were modified through different oxidative treatments and functionalization reactions. The modified SWCNT powders were dispersed in four different aqueous media and purified by ultracentrifugation. Extinction coefficients of the modified SWCNTs depended on the SWCNT type but did not depend on the dispersion medium. According to visible/near infrared spectroscopy, the purity of all the modified SWCNT dispersions substantially improved after ultracentrifugation; however, the spectrum profile, the degree of purity and the centrifugation yield were influenced by the SWCNT type, the surface functional groups and the dispersion medium. Semi-quantitative purity indexes calculated from optical absorption spectra were supported by transmission electron microscopy observations. Contents in metal impurities were analyzed by energy dispersive X-ray spectroscopy. SWCNT samples processed by oxidative acid treatments and ultracentrifugation showed metal contents of lower than 0.5 wt%.     

Raman characterisation of single-walled carbon nanotubes produced by the catalytic pyrolysis of methane

Bundles of single-wall carbon nanotubes (SWCNT) were synthesised using a chemical vapour deposition technique. This basic process was optimised over a wide range of process parameters. For the optimal results, ethane was decomposed at 950 °C over a catalyst material consisting of 2% by wt Fe chemically deposited on an MgO support. The samples were characterised using scanning electron microscopy and transmission electron microscopy to show the presence of nanotubes and also to measure their diameters and the size of amorphous carbon deposits. Raman scattering was also used to probe the electronic properties and hence derive the distribution of diameters of the SWCNT. Samples were measured in both the radial breathing mode and tangential mode ranges using three different laser lines. For comparison purposes, similar data have been reported for a standard commercial SWCNT material (HiPCO). From the data, we can conclude that the tubes in our sample are significantly different to those in the HiPCO sample. In particular, we conclude that samples produced by our method contain a much narrower distribution of tube diameters than does the commercial sample.     

Huge volume expansion and structural transformation of carbon nanotube aligned arrays during electrical breakdown in vacuum

We observed a huge volume expansion of aligned single walled carbon nanotube (SWCNT) arrays accompanied by structural transformation during electrical breakdown in vacuum. The SWCNT arrays were assembled between prefabricated palladium source and drain electrodes of 2 μm separation on a silicon/silicon dioxide substrate by dielectrophoresis. At high electrical field, the SWCNT arrays erupt into a large mushroom-like structure. Systematic studies with controlled electrical bias show that above a certain field the SWCNTs swell and transform to nanoparticles and flower-like structures with a small volume increase. Further increases in electrical bias and repeated sweeping results in their transformation into amorphous carbon as determined from scanning electron microscopy and transmission electron microscopy (TEM). Cross-sectional studies using a focused ion beam and TEM show the height of a 2–3 nm SWCNT array increased to about 1 μm with a volume increase of ～400 times. Electron energy loss spectroscopy reveals that graphitic sp² networks of SWCNT are transformed predominantly to sp³. The current–voltage measurements also show an increase in the resistance of the transformed structure.     

Raman intensity measurements of single-walled carbon nanotube suspensions as a quantitative technique to assess purity

A method to assess the purity of single-walled carbon nanotube (SWCNT) bulk samples based on Raman spectroscopy is reported. The new method has higher reproducibility and quantitative precision than those previously used. It consists of measuring the G-band intensity of liquid suspensions of SWCNT samples as a function of solid concentration. A simple equation is proposed in which one of the two adjustable parameters is the SWCNT purity. The method has been applied to a series of samples of similar characteristics, but varying quality. The results are compared to those obtained on the same series of samples using standard analytical techniques, including electron microscopy, thermogravimetric analysis and optical absorption.     

Self organisation and photoinduced charge transfer in single-wall carbon nanotubes embedded in a thermotropic liquid crystal polymer

A hybrid material composed by a thermotropic liquid crystal (LCP) polymer (HBA–PET) and single wall carbon nanotubes has been produced in order to study the interaction at the interface matrix/filler for possible applications in electronics and optics. The nanocomposites are characterized by a mosaic-like morphology, with regions of randomly placed LC fibers intercalated with regions formed by aligned polymer fibers, that trigger in turn the alignment of carbon nanotube bundles by means of P stacking interaction. Moreover an effective electronic interaction between the nanocomposite components is demonstrated by combining use of photoluminescence and Raman spectroscopy. The photoinduced charge transfer between SWCNT and polymer could be explain on the basis of the injection of holes (generated in the polymer by light absorption), into the SWCNT valence band and followed by a radiationless decay of the excited polymer’s electron.     

Selective synthesis of single-walled carbon nanotubes on Fe–MgO catalyst by chemical vapor deposition of methane

The selective synthesis of single-walled carbon nanotubes (SWCNTs) with narrow chirality and diameter distribution by methane decomposition over Fe–MgO catalyst is reported. The catalyst was examined by nitrogen physisorption, X-ray diffraction, temperature programmed reduction, X-ray photoelectron spectroscopy, and UV–Vis diffuse reflectance spectroscopy to elucidate the structure and chemical state of the species responsible for SWCNT growth. High resolution electron microscopy, Raman and optical absorption spectroscopy, temperature programmed oxidation, energy dispersive X-ray spectroscopy and nitrogen physisorption were used to probe reaction selectivity, SWCNT chirality and diameter distribution, carbon yield and effectiveness of purification protocols. The yield of carbon increased with an increase in temperature, although SWCNTs selectivity decreased above the optimum synthesis temperature. Results established a clear link between the degree of dispersion of iron oxide species inside the MgO lattice and the catalyst selectivity for SWCNT growth.     

原位法制备聚甲基丙烯酸钐/丁腈橡胶纳米复合材料及其反应过程

采用Sm(OH)3和甲基丙烯酸(MA)经原位反应合成Sm(MA)3,以过氧化物为硫化体系制备了聚甲基丙烯酸钐[ Poly -Sm( MA)3]/丁腈橡胶(NBR)纳米复合材料,利用扫描电子显微镜、透射电子显微镜、傅里叶变换红外光谱以及广角X射线衍射分析研究了复合材料制备中的原位聚合过程.结果表明,有机稀土盐单体在原位分...