Synthesis of multi-walled carbon nanotube/polyhedral oligomeric silsesquioxane nanohybrid by utilizing click chemistry

A new hybrid material consisting of a polyhedral oligomeric silsesquioxane (POSS) and carbon nanotube (CNT) was synthesized by a simple and versatile approach entailing click coupling between azide moiety-functionalized POSS and alkyne-functionalized multi-walled CNTs. This approach provides a simple and convenient route to efficiently functionalize a wide variety of nanoscale nanostructure materials on the surface of CNTs.     

Effect of interfacial chemistry on crystallization of polypropylene/multiwall carbon nanotube nanocomposites

This study systematically investigates the polymer–carbon nanotube (CNT) interaction when the interphase is tailored. Maleic anhydride‐grafted‐polypropylene (MA‐g‐PP) or polypropylene (PP) was noncovalently coated onto acid functionalized multiwall nanotube (f‐MWNT) through solution mixing. These coated f‐MWNTs were melt microcompounded with neat PP to form PP/f‐MWNT nanocomposites. The effects of functional groups and the thin layer of solution processed polymers, namely, MA‐g‐PP or PP, at the PP/f‐MWNT interface on crystallization and on melting behavior of matrix PP were investigated. The results were compared with a pristine MWNT (p‐MWNT) incorporated system. It was shown that PP coated CNTs can serve as a strong nucleating agent for templated polymer crystal growth. Unlike other PP nanocomposites in the literature, a relatively high shift of 7°C in melting peak maximum (T_p), along with a sharp melt endotherm was achieved with the addition of 0.3 wt% f‐MWNT via PP/f‐MWNT master batch. This indicates refinement of matrix PP crystalline region due to the tailored f‐MWNT surface chemistry. With a designed self‐seeding and templated crystal growth approach, columnar crystalline interphases were found surrounding MWNT which melted at 10.5°C higher temperature than neat PP crystallized without undergoing the same heat treatment protocol. POLYM. ENG. SCI., 59:1570–1584 2019. © 2019 Society of Plastics Engineers     

Electrically conductive superhydrophobic octadecylamine-functionalized multiwall carbon nanotube films

Electrically conductive, superhydrophobic multiwall carbon nanotube (MWCNT) thin films were prepared by direct amination of MWCNTs with up to 14 wt.% of octadecylamine (ODA) by vacuum filtration method. The ODA-functionalized MWCNT films exhibit a high water contact angle of 165° and electrical conductivity of 860 S/m. The liquid–air–solid interface is directly observed from above the water droplet using an optical microscope. The observation indicates that the wettability state of the MWCNTs has changed from relatively hydrophilic to superhydrophobic state upon functionalization with ODA. The fundamental mechanisms responsible for the unusual combination of surface superhydrophobicity and high electrical conductivity of the MWCNT films are described and their implications are discussed.     

Fabrication of polymer-derived ceramics with hierarchical porosities by freeze casting assisted by thiol-ene click chemistry and HF etching

The freeze casting technique assisted with cryo thiol-ene photopolymerization is successfully employed for the fabrication of macroporous polymer-derived silicon oxycarbide with highly aligned porosity. It is demonstrated that the free radical initiated thiol-ene click reaction effectively cross-linked the vinyl-containing liquid polysiloxanes into infusible thermosets even at low temperatures. Furthermore, mixed solution- and suspension-based freeze casting is employed by adding silica nanopowders. SiOC/SiO₂ foams with almost perfect cylindrical shapes are obtained, demonstrating that the presence of nano-SiO₂ does not restrict the complete photoinduced cross-linking. The post-pyrolysis HF acid treatments of produced SiOC monoliths yields hierarchical porosities, with SiOC/SiO₂ nanocomposites after etching demonstrating the highest specific surface area of 494 m²/g and pore sizes across the macro-, meso- and micropores ranges. The newly developed approach gives a versatile solution for the fabrication of bulk polymer-derived ceramics with controlled porosity.     

Conductive shape-memory polyurethane/multiwall carbon nanotube nanocomposite aerogels

Smart nanocomposite aerogels have promising applications. In this work, different percentages of multiwall carbon nanotube (MWCNT) added into synthesized polyurethane (PU) gel in the molten state, using a two-roll mill. By soaking the PU/MWCNT nanocomposite gel into the water, PU/MWCNT hydrogels containing more than 90 wt % of water were prepared. The obtained hydrogels were freeze-dried to produce aerogel counterparts. The aerogels were fully characterized using mercury porosimetry, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE-SEM). The electrical percolation threshold of conductive aerogel system was measured. The shape-memory behavior of PU/MWCNT nanocomposite aerogels was evaluated by dynamic mechanical thermal analysis (DMTA). The results of the DMTA showed that by adding 2.75 wt % of MWCNT, the recovery ratio and storage modulus of the PU/MWCNT nanocomposite aerogel increased 42 and 180%, respectively. The electrical conductivity of the system also increased three orders of magnitude at the percolation threshold. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48602.     

Highly conductive multiwall carbon nanotube and epoxy composites produced by three-roll milling

Length and diameter distributions as well as the conductivity of bucky papers made of different multiwalled carbon nanotubes (MWCNTs) have been measured. While the average diameter is in good agreement with the manufacturer specification, the average length is significantly shorter than that given by the manufacturer. Highly conductive and homogeneous dispersions of up to 8 wt% MWCNTs in an epoxy resin are obtained by three-roll milling. The influence of shear intensity and number of passes on the nanotube dispersion and composite conductivity is investigated. The aspect ratio of the MWCNTs is one of the most important parameters that determine the composite conductivity and the percolation behavior. We have found that the composite conductivity increases almost 10 times as the aspect ratio increases 5.5 times. The percolation parameters in conjunction with the optical microscopy revealed a kinetic rather than statistic percolation. We have observed that three-roll milling induces extended alignment of MWCNTs with high aspect ratio at moderate loading (2-4 wt%).     

Focused-ion-beam assisted fabrication of individual multiwall carbon nanotube field emitter

We report the fabrication of an individual carbon nanotube (CNT) electron field emitter using a focused-ion-beam (FIB) technique. The monolithic multiwall CNT with a graphitic shield is synthesized using chemical vapor deposition technique. The FIB technique is applied to attach the monolithic multiwall CNT on an etched tungsten tip. Field emission measurements are carried out in a vacuum of 10⁻⁷ Torr. Threshold voltage as low as 120 V has been obtained.     

Characterization of conductive multiwall carbon nanotube/polystyrene composites prepared by latex technology

Conductive multiwall carbon nanotube/polystyrene (MWCNT/PS) composites are prepared based on latex technology. MWCNTs are first dispersed in aqueous solution of sodium dodecyl sulfate (SDS) driven by sonication and then mixed with different amounts of PS latex. From these mixtures MWCNT/PS composites were prepared by freeze-drying and compression molding. The dispersion of MWCNTs in aqueous SDS solution and in the PS matrix is monitored by UV–vis, transmission electron microscopy, electron tomography and scanning electron microscopy. When applying adequate preparation conditions, MWCNTs are well dispersed and homogeneously incorporated in the PS matrix. The percolation threshold for conduction is about 1.5 wt% of MWCNTs in the composites, and a maximum conductivity of about 1 S m⁻¹ can be achieved. The approach presented can be adapted to other MWCNT/polymer latex systems.     

Modeling of creep for multiwall carbon nanotube/epoxy nanocomposite

The effect of multiwall carbon nanotubes (MWCNTs) on creep of epoxy matrix was evaluated on the basis of short‐term creep‐recovery tests performed at different stresses and temperatures. Six different compositions of MWCNT and bisphenol A epoxy resin (0–3.8 wt % of MWCNTs) were investigated. Slight reduction of creep compliance, strain rate, and residual strain were revealed experimentally for nanocomposite comparing to the neat resin. The development of viscoelastic strain for creep stage was described by the use of time–temperature–strain superposition principle with the parameters obtained from the approximation of recovery stage using modified Schapery model. The model accounted for the effect of strain on the viscoelastic strain rate for recovery stage. Its application gave better results for approximation of a series of recovery curves at different temperatures and stresses than of time–stress superposition model. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

多壁碳纳米管/两亲性嵌段聚合物复合材料的制备

采用两亲性三嵌段聚合物PAN-PEG-PAN的DMF溶液分散MWNTs,通过静电纺丝制备MWNTs/PAN-PEG-PAN复合纤维.采用流变仪与SEM分析了MWNTs的分散性以及MWNTs对复合材料的结构性能的影响.结果表明:MWNTs/PAN-PEG-PAN溶液的模量与粘度随着MWNTs的质量分数的增加而增加,当MW...     

Physical properties of phenol-anchored multiwall carbon nanotube/epoxy nanocomposite

Surface functionalization of multiwall carbon nanotubes (MWCNTs) was carried out by introducing a ylide group containing anchored phenol structures. Epoxy nanocomposites filled with modified and pristine carbon nanotubes were prepared, and their mechanical, electrical, and thermal properties were evaluated. Mechanical properties such as tensile strengths and Young’s moduli of the epoxy nanocomposites increased significantly with the addition of the modified MWCNTs compared to the pristine MWCNTs, due to the strong interaction between the modified MWCNTs and the epoxy matrix. Scanning electron microscopy of the fractured epoxy systems revealed that the functionalized MWCNTs were finely dispersed in the matrix, as opposed to the pristine carbon nanotubes. The epoxy/functionalized MWCNT nanocomposite had a lower surface electrical resistance than the epoxy/pristine MWCNT nanocomposite, confirming the effect of functionalization.     

Anisotropic interfacial friction of inclined multiwall carbon nanotube array surface

Anisotropic interfacial friction of an inclined, multiwalled carbon nanotube (MWCNT) array surface fabricated on a commercial electrostatic adsorption film substrate has been experimentally studied. As a typical case, the friction force of steel ball/inclined MWCNT along the inclined direction is 40% larger than that against the inclined direction. The significant interfacial friction anisotropy remains stable even after nearly 4000 sliding cycles. While the tilt of MWCNT close to the top surface layer significantly affected the interfacial friction, the underlying nanotubes only has limited effects. Based on the van der Waals interaction between the MWCNT and the steel ball, the achieved anisotropic interfacial friction at different sliding directions is quantitatively modeled and explained. The interplay between the lateral friction and normal adhesion force has also been found during the unloading process of friction test.     

Carbon nanotube functionalization effects on thermal properties of multiwall carbon nanotube/polycarbonate composites

The thermal properties of composites based on polycarbonate (PC) filed with ultraviolet/ozone (UVO) treated multiwall carbon nanotubes (MWCNTs) in low limit (less than 0.01) volume fractions have been investigated. The composites were prepared in the form of films of relatively small thickness (23–33 μm) with random orientation of treated MWCNTs. Functionalization of MWCNTs has been confirmed through Fourier transform infrared measurements. Thermal conductivity was obtained by measuring both of thermal diffusivity and thermal effusivity using photoacoustic technique. The results reveal that the addition of UVO treated MWCNTs lead to enhance both the thermal diffusivity and thermal effusivity of the composites. Insertion of 0.95% MWCNTs into PC improves the thermal conductivity of the composites by ∼22%. This enhancement is reasonable using such low content of MWCNTs of moderate aspect ratio. The experimental results were analyzed using a simple model concerning some relevant parameters such as volume fractions, interfacial thermal resistance, aspect ratio, and nonstraightness of nanotubes. An interface thermal resistance in the low limit of about 2.1 × 10⁻⁸ m²K/W has been estimated. In the light of these results, the role of MWCNTs functionalization on the overall thermal transport properties of MWCNTs‐polymer composites has been discussed. POLYM. COMPOS., 36:1242–1248, 2015. © 2014 Society of Plastics Engineers     

Tunable dielectric properties in polyacrylonitrile/multiwall carbon nanotube composites

Composites containing polyacrylonitrile (PAN) and different mass contents of multiwall carbon nanotubes (MWCNTs) were prepared and structurally investigated. X‐ray Diffraction of pristine PAN reveals the presence of crystalline and amorphous phases which change their ratio under thermal annealing and addition of MWCNT. For as prepared samples, thermal analysis reveals two glass transition temperatures, which support the hypothesis that unoriented PAN is a two‐phase material. Infrared spectrum of as prepared PAN suggests that the polymer is not stabilized. Dielectric investigations of PAN/MWCNT composites show that permittivity has a strong increase as the MWCNT mass content increases, while the dielectric losses are comparable in all samples. These results suggest that PAN/MWCNT composites could find important applications in electronics. POLYM. COMPOS., 38:1741–1748, 2017. © 2015 Society of Plastics Engineers     

Formation of thin boron nitride coating on multiwall carbon nanotube surfaces

Thin boron nitride films were deposited onto outer surfaces of multiwall carbon nanotubes (MWCNTs) by dip coating, which involves infiltration by boric acid solutions and subsequent nitridation of the boron oxide in ammonia flow at 1050 °C. The overall composition of the samples was determined by electron energy loss (EELS) and X-ray photoelectron spectroscopy (XPS), the surface composition and chemical structure of the BN coatings by XPS, the morphology of the BN/MWCNT composites by scanning and transmission electron microscopy (SEM, TEM), and the resistance against oxidation at elevated temperatures by thermal analysis (TGA). It was proved that single and multilayer BN coverage were achieved at the applied experimental conditions, and the coated samples showed significantly increased oxidation resistance compared to the uncoated MWCNTs.     

Electrical and dielectric properties of multiwall carbon nanotube/polyaniline composites

In this paper, electrical and dielectric properties of multiwall carbon nanotubes (MWCNTs)/insulating polyaniline (PANI) composites were studied. A mixture of MWCNTs and insulating polyaniline was dispersed in an ethanol solution by ultrasonic process, subsequently dried, and was hot-pressed at 200 °C under 30 MPa. Electrical and dielectric properties of the composites were measured. The experimental results show that the dc conductivities of the composites exhibit a typical percolation behavior with a low percolation threshold of 5.85 wt.% MWCNTs content. The dielectric constant of the composites increases remarkably with the increasing MWCNTs concentration, when the MWCNTs concentration was close to percolation threshold. This may be attributed to the critical behavior of the dielectric constant near the percolation threshold as well as to the polarization effects between the clusters inside the composites.     

Synthesis and characterization of multiwall carbon nanotube/waterborne polyurethane nanocomposites

The preparation of thermoplastic nanocomposites of waterborne polyurethane (WBPU) and multiwall carbon nanotubes (MWCNTs) via an in situ polymerization approach is presented. The effects of the presence and content of MWCNTs on the morphology and thermal, mechanical and electrical properties of the nanocomposites were investigated. Carbon nanotubes were modified with amide groups in order to enhance their chemical affinity towards WBPU. Thermogravimetric studies show enhanced thermal stability of the nanocomposites. Scanning and transmission electronic microscopy images prove that functionalized carbon nanotubes can be effectively dispersed in WBPU matrix. Mechanical properties reveal that Young's modulus and tensile strength tend to increase when appropriate amounts of MWCNTs are loaded due to the reinforcing effect of the functionalized carbon nanotubes. Thermal properties show an increase in the glass transition temperature and storage modulus with an increase in MWCNT content. X‐ray diffraction reveals better crystallization of the WBPU in the presence of MWCNTs. The WBPU/MWCNT nanocomposite film containing 1 wt% of MWCNTs exhibits a conductivity nearly five orders of magnitude higher than that of WBPU film. © 2017 Society of Chemical Industry     

In-situ generation of a well-dispersed multiwall carbon nanotube/syndiotactic polystyrene composite using pentamethylcyclopentadienyltitanium trimethoxide anchored to multiwall carbon nanotubes

A well-dispersed multiwall carbon nanotube (MWCNT)/syndiotactic polystyrene (sPS) composite was prepared by simple in-situ polymerization of styrene using pentamethylcyclopentadienyltitanium(IV) trimethoxide (Cp*Ti(OMe)₃) attached to the shortened and functionalized MWCNT (f-MWCNT). The attachment of Cp*Ti(OMe)₃ to the f-MWCNT was confirmed by thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy, and energy dispersive X-ray spectroscopy. Cp*Ti(OMe)₃ attached to pristine MWCNT in the presence of methylaluminoxane (MAO) did not produce PS, whereas Cp*Ti(OMe)₃ attached to f-MWCNT showed a high catalytic activity for the syndiospecific polymerization of styrene under the same polymerization conditions. Obtained sPS showed a narrow molecular weight distribution (PDI ≈ 2), a high SI value (≥90%), and a high melting point (≈272 °C). Scanning electron microscopy and transmission electron microscopy images showed that MWCNT strands were well dispersed in the MWCNT/sPS composite. Such composites had greatly improved thermal stability compared to normal sPS polymers.     

Methods to assess the impact of UV irradiation on the surface chemistry and structure of multiwall carbon nanotube epoxy nanocomposites

One of the most promising applications of nanomaterials is as nanofillers to enhance the properties of polymeric materials. However, the effect of nanofillers on polymers subjected to typical environmental stresses, such as ultraviolet (UV) radiation, high humidity, or elevated temperatures, is not well understood. This stems partly from a lack of a single analytical method to assess these impacts. In this study, multiwall carbon nanotube (MWCNT) epoxy nanocomposite materials were exposed to carefully controlled UV doses (equivalent of up to ≈4 years in Florida). A suite of microscopic, spectroscopic and gravimetric techniques were optimized and used to assess changes occurring in the sample mass, surface chemistry, and surface and sub-surface morphology after UV irradiation. Overall, photodegradation of the epoxy matrix was retarded by the presence of the 3.5% MWCNT filler, suggesting that MWCNTs may enhance the lifetime of nanocomposite materials. Multiple microscopic and spectroscopic techniques clearly showed accumulation of MWCNTs on the nanocomposite surface that grew with increasing UV dose, a finding that may be significant with regard to the potential risk of MWCNT release during the nanocomposite lifetime. These analytical methods will help enable a robust and informative assessment of transformations in polymer nanocomposites subject to environmental stresses.     

Thermal properties of hyperbranched polyborate functionalized multiwall carbon nanotube/polybenzoxazine composites

Using a noncovalent functionalization strategy, hyperbranched polyborate (HBb) acts as a solubilizer for carbon nanotubes (CNTs), and a stable HBb‐CNT dispersion in N‐methyl‐pyrrolidone was produced. The thermal properties of the resulting HBb‐CNT/polybenzoxazine (B‐BOZ) composites and their carbonized structures were investigated. Scanning electron microscopy demonstrated that the fracture surface of HBb‐CNT/B‐BOZ composites was rather rough and plenty of plastic deformation was exhibited. Thermogravimetric analysis indicates an improvement in the thermal stability of the composite with CNTs, especially that of 2.0 wt% CNT modified composite. The increase in the thermal stability is due to the good nanotube dispersion and the effective polymer‐CNT interaction. Graphite‐like boron carbonitride ceramic compounds were found after the composites were carbonized at 1,100°C for 2 h, and there was more B‐C, B‐N, and C‐N bonds in the carbonized HBb‐CNT/B‐BOZ composite than that of HBb/B‐BOZ composite. The result implied that CNTs can promote the ceramic process of HBb/B‐BOZ composite, and the strategy of introducing ceramic precursor into polymer composites may be useful to improve their ablation properties. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers