Multiwall carbon nanotubes: synthesis and application

Chemical vapor deposition (CVD) is the most promising synthesis route for economically producing large quantities of carbon nanotubes. We have developed a low-cost CVD process for the continuous production of aligned multiwall carbon nanotubes (MWNTs). Here we report the effects of reactor temperature, reaction time, and carbon partial pressure on the yield, purity, and size of the MWNTs produced. A simple method for purifying and healing structural defects in the nanotubes is described. The dispersion of nanotubes in polymer matrices has been investigated as a means of deriving new and advanced engineering materials. These composite materials have been formed into fibers and thin films and their mechanical and electrical properties determined.     

Multiwall carbon nanotubes grown by thermocatalytic carbonization of polyacrylonitrile

A method is reported for the growth of multiwall carbon nanotubes (MWCNTs) using polyacrylonitrile as a solid carbon source and nanosized SiO₂ particles as catalyst. The nanotubes were grown either on a Si substrate or as a freestanding film at temperatures as low as 800 °C. The smallest measured inner diameter of the resultant MWCNTs is about 0.6 nm and therefore this method provides a new direction to prepare MWCNTs with very small inner diameter from solid carbon source.     

自由基聚合制备甲基丙烯酸甲酯-苯乙烯嵌段共聚物

以偶氮二异丁腈为引发剂,乙二硫醇（EDT）为链转移剂进行甲基丙烯酸甲酯（MMA）的自由基聚合,得到了含有残余巯基的聚甲基丙烯酸甲酯大分子链转移剂（HS-PMMA）,继而以HS-PMMA作为大分子链转移剂进行苯乙烯的自由基聚合,采用普通自由基聚合方法合成了结构可以设计的嵌段共聚物。     

Multiwall carbon nanotubes filled polypropylene nanocomposites: Rheological and electrical properties

Two types of commercial multiwall carbon nanotubes (MWCNTs), Baytubes® C70P and C150P were incorporated into polypropylene (PP) using melt blending technique that employs a twin screw extruder (TSE) to prepare the nanocomposites of two different concentrations (1 and 3 wt%). Subsequently, American Society for Testing and Materials (ASTM) standard samples were prepared with an injection molding machine. The prepared nanocomposites were characterized by their rheological and electrical properties using a rheometer and a picoammeter/voltage source, respectively. The effect of different types of MWCNTs and loading percentage in rheological and electrical properties was investigated in detail. The rheological analysis demonstrated a considerable dependence of the melt rheological properties of the PP/MWCNTs nanocomposites on the MWCNTs loading. The storage modulus (G′), loss modulus (G″) and complex viscosity increased with increasing MWCNTs loading. In addition, type C70P exhibited superior rheological properties compared to C150P. In terms of electrical properties, the addition of MWCNTs in the PP matrix decreased the volume resistivity of the matrix in a manner, proportional to the MWCNTs loading. No significant difference in volume resistivity was observed between the MWCNTs types. POLYM. ENG. SCI., 54:1134–1143, 2014. © 2013 Society of Plastics Engineers     

Microstructure determination of isobornyl methacrylate-styrene copolymer by NMR spectroscopy

An investigation of the microstructure of isobornyl methacrylate - styrene (I/S) copolymers prepared by the atom transfer radical polymerization (ATRP) using methyl-2-bromopropionate as an initiator and PMDETA copper complex as catalyst under nitrogen atmosphere at 70 °C has been done by two-dimensional NMR techniques. 2D- HSQC and TOCSY have been utilized to resolve the complex ¹H NMR spectrum and to establish the compositional and configurational sequences of isobornyl methacrylate-styrene (I/S) copolymers. 2D HSQC and TOCSY spectra showed compositional and configurational sensitivity of α-methyl carbon of I unit and methine proton of S unit and are assigned up to the triad level. The methylene carbon (C₁₀) also shows triad level of compositional sensitivity in 2D HSQC spectra. Heteronuclear multiple-bond correlation (HMBC) spectroscopy has been used to study carbonyl/quaternary carbon-proton coupling. The carbonyl and quaternary carbons showed compositional and configurational sensitivity upto the triad level. The values of reactivity ratios were determined by Kelen-Tudos (KT) and nonlinear error in variable method (RREVM) using copolymer composition data that were determined by ¹H NMR spectrum. Reactivity ratios of co-monomers in I/S copolymer, determined from a linear Kelen-Tudos method (KT) and non-linear Error-in-Variable Method (EVM), are r_I?=?0.39?±?0.09, r_S?=?0.44?±?0.08 and r_I?=?0.42, r_S?=?0.47, respectively.     

Crystallization induced block copolymer decoration on carbon nanotubes

A unique noncovalent means to decorate block copolymers on carbon nanotubes (CNTs) using a controlled polymer crystallization method is presented. Transmission electron microscope observation and electron diffraction result demonstrated the surface functionalization of CNTs with a crystalline-noncrystalline triblock copolymer poly(vinylcyclohexane)-b-poly(ethylene)-b-poly(vinylcyclohexane) (PVCH-PE-PVCH), forming a novel nano-hybrid epitaxial brush structure, which consists of a central CNT and disc-shaped folded-chain lamellae of PE blocks with random coils of amorphous PVCH blocks surrounding them.     

Toughening effect of EPDM-graft-methyl methacrylate and styrene (EPDM-g-MMA-St) on methyl methacrylate-styrene copolymer (MS resin)

EPDM-graft-methyl methacrylate and styrene (EPDM-g-MMA-St) was synthesized by solution graft copolymerization of methyl methacrylate (MMA) and styrene(St) onto ethylene-proplene-diene terpolymer (EPDM) in toluene/n-heptane cosolvent using benzoyl peroxide as an initiator. Fourier transform infrared spectroscopy provides a substantial evidence of grafting of MMA and St onto EPDM. EPDM-g-MMA-St/MS resin blends (MES) were prepared by melt blending EPDM-g-MMA-St and MS resin, and the toughening effects of EPDM-g-MMA-St on MS resin were studied. The results showed that the synthesized conditions of EPDM-g-MMA-St influenced the toughening effect of EPDM-g-MMA-St on MS resin. Notched Izod impact strength of MES increased with increasing grafting ratio, grafting chain polarity of EPDM-g-MMA-St, and EPDM content in MES. Differential scanning calorimetry showed that EPDM-g-MMA-St and MS resin are compatible partially and the compatibility improves with increasing grafting chain polarity of EPDM-g-MMA-St. Transmission electron microscopy and scanning electron microscopy analysis showed that the phase structure was “sea-island” structure, and the particle diameter of EPDM-g-MMA-St increased, meanwhile, surface to surface interparticle distance decreased with an increase in EPDM content, which resulted in the toughening mechanism of MES changed into slight shear yielding of matrix from the damage mode of cavitation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

甲基丙烯酸甲酯-苯乙烯悬浮聚合共聚物粒度的控制

以过氧化二苯甲酰为引发剂,以聚乙烯醇-羟基磷酸钙复合分散体系为分散剂,采用悬浮聚合法制备甲基丙烯酸甲酯-苯乙烯共聚物珠粒.研究了单体配比、引发剂用量、分散剂用量、反应温度、搅拌速度对聚合物珠粒的影响;并用红外光谱对产物结构进行了表征.     

Controlled assembly of carbon nanotubes encapsulated with amphiphilic block copolymer

An amphiphilic diblock copolymer (PEtOz-PCL) based on hydrophilic poly(2-ethyl-2-oxazoline) (PEtOz) and hydrophobic poly(ε-caprolactone) (PCL) was adsorbed in aqueous phase on the surface of single-wall carbon nanotube to produce PEtOz-PCL-encapsulated SWCNTs (PEtOz-PCL/SWCNT) with the diameter about 30 nm. The Raman spectroscopy analysis indicated that the nanotubes were physically encapsulated by the block copolymer without chemical denaturation of the nanotube. PEtOz-PCL/SWCNTs exhibited pH-responsive reversible complexation with poly(acrylic acid) or poly(methacrylic acid) in aqueous phase due to the pH-dependent hydrogen bonding between the PEtOz outer shell of PEtOz-PCL/SWCNTs with carboxyl groups. In addition, by using PEtOz as a template for the formation of metal nanoparticles, Au and Pd nanoparticles were successfully hybridized with PEtOz-PCL/SWCNTs.     

Selective self-assembly of surface-functionalized carbon nanotubes in block copolymer template

Microphase-separated styrene-butadiene-styrene (SBS) triblock copolymer was utilized as a template for the selective self-assembly of polystyrene (PS)-functionalized carbon nanotubes (CNTs) in the PS phase. It was also found that PS-functionalized CNTs could be accommodated in the PS phase of SBS regardless of the molecular weight of the PS ligand. This is different from the case for assembling nanoparticles or nanorods with a block copolymer, in which the ligand should be shorter than the corresponding block such that the nanoparticles or nanorods can be incorporated into that block. This phenomenon is explained based on the different chain morphologies of the ligands functionalizing the CNTs, nanoparticles and nanorods.     

Synthesis of vinylferrocene and the ligand-exchange reaction between its copolymer and carbon nanotubes

To improve the dispersibility of carbon nanotubes (CNTs), poly(vinylferrocene-co-styrene) (poly (Vf-co-St)), was grafted onto the surface of CNTs by a ligand-exchange reaction. Poly(Vf-co-St) was obtained by a radical copolymerization reaction using styrene and vinylferrocene as the monomers. The vinylferrocene was synthesized from ferrocene via a Friedel-Crafts acylation. The molecular weight, molecular weight distribution, and amount of Vf in the poly(Vf-co-St) were 1.32 × 10⁴, 1.69 and 17.6% respectively. The degree of grafting of the copolymer onto the CNTs surface was calculated from thermogravimetric analysis and varied from 27.1% to 79.7%. The addition of the poly(Vf-co-St) greatly promoted the dispersibility of the modified CNTs in anhydrous alcohol. The electrical conductivity of composites prepared from the polymer-grafted CNTs and copolymer (acrylonitrile, 1,3-butadiene and styrene, ABS) strongly depended on the degree of grafting. These results show that the amount of polymer grafted onto the surface of CNTs can be controlled and that the electrical properties of composites prepared with these grafted polymers can be tuned.     

Impact of multiwall carbon nanotubes on the fatigue strength of adhesive joints

This paper presents the results of research undertaken to determine the possibility of improving the fatigue properties of peel-loaded adhesive joints by dispersing multiwall carbon nanotubes (MWCNTs) into epoxy-based adhesives. The fatigue strength tests were carried out on an electromagnetic inductor with the resonance frequency of the adhesively bonded joint specimen. The tests were conducted for three types of epoxy adhesives whose properties were modified through the introduction of multiwalled carbon nanotubes, into their structure. Carbon nanotubes were synthesized by means of the Chemical Vapour Deposition (CVD) method with Fe-Co catalysts. A quantity of 1 wt.% of the dried material was dispersed into the epoxy adhesives. The results of the fatigue strength tests revealed a significant improvement of the fatigue lifetime of adhesive joints due to MWCNT introduction as filler for epoxy adhesives. In the case of the Epidian 57/PAC adhesive composition, a more than twofold increase in the fatigue lifetime was obtained (an increase of 106.8%). For the Bison Epoxy adhesive composition, the fatigue lifetime increased by 69.3%. The fatigue strength for the best result increased by about 13%.     

Localization of carbon nanotubes at the interface in blends of polyamide and ethylene-acrylate copolymer

The present study demonstrates for the first time the possibility to jam unpurified and unfunctionalized multiwall carbon nanotubes (MWNTs) at the interface of an immiscible blend of polyamide (PA) and ethylene-acrylate (EA) copolymer. The confinement appears to be stable. The influence of the mixing strategy and of the polyamide type used has been examined. When the MWNTs are first dispersed in PA6, most of them migrate to the interface although some of them stay in the PA phase. When the MWNTs are first dispersed in PA12, they remain well dispersed in PA. When the MWNTs are first dispersed in the EA copolymer or when the three components are simultaneously mixed, a large part of the MWNTs migrate to the interface whatever the PA used. However, some of the MWNTs remain in the EA phase and when PA12 is used, part of the MWNTs penetrate inside the PA nodules. By a combination of TGA and separation techniques, we show that the first polymer to come in contact with the nanotubes during melt mixing is (at least partially) adsorbed irreversibly, by non-covalent adsorption. The resulting modification of interfacial thermodynamics explains the observed confinement.     

Encapsulation of multi-walled carbon nanotubes with copolymer to disperse in aqueous media

An emulsion-like polymerization technique called admicellar polymerization (AP) was used to encapsulate a thin film of copolymer on the surface of multi-walled carbon nanotubes (MWCNTs). A water-soluble component sodium acrylate and a non-water soluble component methyl methacrylate were used to form thin films of copolymer on multi-walled carbon nanotubes. Various ratios of polymer combinations were formulated on MWCNT’s to understand the stability of polymer composition and surface heterogeneity on MWCNT’s. Encapsulated MWCNTs were characterized using SEM, energy dispersive spectroscopy (EDS), thermal analysis and FT-IR. Analytical studies indicate the formation of copolymer on MWCNTs. Monomer conversion rate and copolymer reactivity ratios were analyzed using high performance liquid chromatography (HPLC) by Fineman-Ross and Kelen-Tüdos methods. The copolymer combination showed an alternating tendency and azeotropic composition at 0.6 acrylate monomer. The encapsulated MWCNTs were stable in aqueous media with onset of aggregate formation beginning at 40 days for the copolymer.     

Reinforcement of styrene-butadiene-styrene tri-block copolymer by multi-walled carbon nanotubes via melt mixing

Styrene-butadiene-styrene tri-block copolymer (SBS) was reinforced with multi-walled carbon nanotubes (MWCNTs) by the interaction through melt mixing. The tensile strength of SBS/MWCNT composites increased with increasing MWCNT content. The interactions between SBS and MWCNTs were characterized by solubility of MWCNTs in tetrahydrofuran, dynamic mechanical analysis, X-ray photoelectron microscope, ultraviolet spectra and transmission electron microscopy. The results showed that there were interactions between MWCNTs and SBS occurred during melt mixing, leading to an improvement of the mechanical properties of SBS/MWCNT composites, as well as the homogeneous dispersion of MWCNTs in SBS. The interactions between MWCNTs and SBS were supposed to consist of the π-π interaction between MWCNTs and the phenyl groups of SBS, as well as the chemical bonding of polybutadiene segments with MWCNTs.     

Characterization of styrene-ethylene oxide and methyl methacrylate-styrene block copolymers by light scattering

Several polystyrene-poly(ethylene oxide)-polystyrene (PS-PEO-PS) and poly(methyl methacrylate)-polystyrene-poly(methyl methacrylate) (PMMA-PS-PMMA) block copolymers, synthesized by free-radical polymerization, were studied in various solvents by using a light-scattering technique. The copolymers, which have different lengths of central blocks, had molecular weights within the range 3.0 × 10⁴ to 1.6 × 10⁶. It was found that almost all of them were confirmed as block copolymers from the variation of the product $\text{M}{}_{\mathrm{<mtext>app</mtext>}}\text{〈S}{}^2{}_{\mathrm{<mtext>app</mtext>}}\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ with $\text{W}{}_{\mathrm{<mtext>A</mtext><mtext>v</mtext><mtext>A</mtext>}}\text{v}$, although they were rather heterogeneous. The copolymer compositions determined either from the additivity of the refractive index increments of its constituent parts and the copolymer or from ultra-violet analysis were in excellent agreement with each other.     

Optimizing the thermoelectric performance of zigzag and chiral carbon nanotubes

Using nonequilibrium molecular dynamics simulations and nonequilibrium Green''s function method, we investigate the thermoelectric properties of a series of zigzag and chiral carbon nanotubes which exhibit interesting diameter and chirality dependence. Our calculated results indicate that these carbon nanotubes could have higher ZT values at appropriate carrier concentration and operating temperature. Moreover, their thermoelectric performance can be significantly enhanced via isotope substitution, isoelectronic impurities, and hydrogen adsorption. It is thus reasonable to expect that carbon nanotubes may be promising candidates for high-performance thermoelectric materials.     

Synergistic effects of carbon nanotubes and carbon black on the fracture and fatigue resistance of natural rubber composites

The quasi‐static fracture and dynamic fatigue behaviors of natural rubber composites reinforced with hybrid carbon nanotube bundles (CNTBs) and carbon black (CB) at similar hardness values were investigated on the basis of fracture mechanical methods. Mechanical measurement and J‐integral tests were carried out to characterize the quasi‐static fracture resistance. Dynamic fatigue tests were performed under cyclic constant strain conditions with single‐edged notched test pieces. The results indicate that synergistic effects between CNTBs and CB on the mechanical properties, fracture, and fatigue resistance were obtained. The composite reinforced with 3‐phr CNTBs displayed the strongest fatigue resistance. The synergistic mechanisms and dominating factors of quasi‐static and dynamic failure, such as the dispersion state of nanotubes, hybrid filler network structure, strain‐induced crystallization, tearing energy input, and viscoelastic hysteresis loss, were examined. The weakest fatigue resistance of the composite filled with 5‐phr CNTBs was ascribed to its strikingly high hysteresis, which resulted in marked heat generation under dynamic fatigue conditions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42075.