Fabrication of hybrid ladderlike polysilsesquioxane‐grafted multiwalled carbon nanotubes

Ladderlike polysilsesquioxanes (LPSs) containing chloromethylphenyl groups were synthesized from (p‐chloromethyl)phenyltrimethoxysilane under basic conditions. Functionalized multiwalled carbon nanotubes (MWNT–COOH) were prepared by the acid treatment of pristine multiwalled carbon nanotubes (MWNTs). MWNT–COOH was reacted with LPS to prepare LPS‐grafted MWNTs via ester linkages. The functionalization of MWNTs with LPS significantly altered the surface roughness of the MWNTs; there was a significant increase in the diameter of the MWNTs. The LPS‐grafted MWNTs had a 10–20 nm thickness along the outer walls according to the functionalization of the MWNTs with LPS. An advantage of the hybrid LPS‐grafted MWNTs was shown as improved thermal behavior. The composition, thermal properties, and surface morphology of the LPS‐grafted MWNTs were studied by Fourier transform infrared spectroscopy, thermogravimetric analysis, energy‐dispersive spectroscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of novel hybrid polyoxazoline‐grafted multiwalled carbon nanotubes

The novel hybrid polyoxazoline‐grafted multiwalled carbon nanotubes (POZO‐grafted MWNTs) were synthesized by the reaction of partially hydrolyzed polyoxazolines (Hydrolyzed‐POZO) and MWNTs having carboxylic acid groups (MWNT‐COOH) in the presence of DCC as a condensing agent. Hydrolyzed‐POZO (degree of hydrolysis, 20.2 mol % by ¹H‐NMR) were produced from the hydrolysis of polyoxazolines in an aqueous NaOH solution at reflux for 72 h. MWNT‐COOH were prepared by acid treatment of pristine MWNTs. The composition, structure, thermal property, and surface morphology of the novel hybrid POZO‐grafted MWNTs were fully characterized by FT‐IR, Raman, ¹H‐NMR, DSC, TGA, SEM, and TEM. The obtained POZO‐grafted MWNTs are well soluble in various organic solvents and water. It was observed that the glass transition temperature (T_g) of POZO‐grafted MWNTs was lower than that of Hydrolyzed‐POZO due to the absence of hydrogen bonding interactions between Hydrolyzed‐POZO itself caused by the incorporation with MWNTs. It was also found that Hydrolyzed‐POZO was homogeneously attached to the surfaces of MWNTs through the “grafting‐to” method. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Enhancement of the surface and bulk mechanical properties of polystyrene through the incorporation of raw multiwalled nanotubes with the twin‐screw mixing technique

In this article, we present the effects of incorporated multiwalled nanotubes (MWNTs) on a metal surface and the bulk mechanical properties of as‐synthesized polystyrene (PS)–MWNT composites prepared with the twin‐screw mixing technique. The MWNTs used for preparing the composites were raw compounds that were not treated with any surface modifications. The morphology for the dispersion capability of the MWNTs in the PS matrix was subsequently characterized with transmission electron microscopy. Surface mechanical property studies (i.e., wear resistance and hardness) showed that the integration of MWNTs led to a distinct increase in the wear resistance and also the micro/nanohardness with up to a 5 wt % MWNT loading in the composites. Moreover, the enhancement of the wear resistance of the as‐prepared composites, in comparison with pure PS, was further identified with scanning electron microscopy observations of the surface morphology after testing. On the other hand, for bulk mechanical property studies (i.e., the tensile strength and flexural strength), the composites containing a 3 wt % concentration of MWNTs in the PS matrix exhibited the best performance with respect to the tensile strength and flexural strength. This means that this composition of MWNTs exhibited good compatibility with the PS matrix, and this can be attributed to the π–π interacting forces existing between the aromaticity of the MWNTs and PS matrix. Furthermore, at higher MWNT loadings (e.g., 5 wt %), raw MWNTs were aggregated in the polymer matrix, as observed by transmission electron microscopy. Also, this led to an obvious decrease in the tensile strength and flexural strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

High electrical conductivity of nylon 6 composites obtained with hybrid multiwalled carbon nanotube/carbon fiber fillers

The synergetic effect of multiwalled carbon nanotubes (MWNTs) and carbon fibers (CFs) in enhancing the electrical conductivity of nylon 6 (PA6) composites was investigated. To improve the compatibility between the fillers and the PA6 resin, we grafted γ‐aminopropyltriethoxy silane (KH‐550) onto the MWNTs and CFs after carboxyl groups were generated on their surface by chemical oxidation with nitric acid. Fourier transform infrared spectroscopy and thermogravimetric analysis proved that the KH‐550 molecules were successfully grafted onto the surface of the MWNTs and CFs. Scanning electron microscopy and optical microscopy showed that the obtained modified fillers reduced the aggregation of fillers and resulted in better dispersion and interfacial compatibility. We found that the electrical percolation threshold of the MWNT/PA6 and CF/PA6 composites occurred when the volume fraction of the fillers were 4 and 5%, respectively. The MWNT/CF hybrid‐filler system exhibited a remarkable synergetic effect on the electrically conductive networks. The MWNT/7% CF hybrid‐filler system appeared to show a second percolation when the MWNT volume fraction was above 4% and a volume resistivity reduction of two orders of magnitude compared with the MWNT/PA6 system. The mechanical properties of different types of PA6 composites with variation in the filler volume content were also studied. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40923.     

Constructing polymer brushes on multiwalled carbon nanotubes by in situ reversible addition fragmentation chain transfer polymerization

A fascinating nanoobject, diblock polymer brushes with a hard core of multiwalled carbon nanotubes (MWNTs) and a relatively soft shell of poly(methylmethacrylate)-block-polystyrene (PMMA-b-PS), was easily constructed by in situ reversible addition fragmentation chain transfer polymerization (RAFT) of methylmethacrylate followed by styrene (St) on the modified convex surfaces of MWNTs (MWNT-PMMA). The structure and morphology of the hybrid nanomaterials were characterized by FTIR, TEM, SEM, NMR, DSC and TGA. The results showed that both styrene and acrylate type monomers can be easily initiated and then propagated on the MWNT sidewalls via the in situ RAFT approach, and the length of the PS blocks increases with increasing St:MWNT-PMMA weight feed ratio.     

Preparation and characterization of thermally conductive polystyrene/carbon nanotubes composites

Thermally conductive polystyrene (PS)/multi‐walled carbon nanotubes (MWNTs) nanocomposites was prepared through a simple solution‐evaporation method assisted by ultrasonic irradiation. To enhance the dispersion of MWNTs in PS, MWNTs were chemically functionalized with poly(styrene‐co‐maleic anhydride) (SMA) (MWNT‐g‐SMA), which had benzene group and exhibited strong affinity with PS. The thermal conductive properties of PS increased and the mechanical properties decreased in presence of MWNTs, while by addition of MWNT‐g‐SMA, the properties of the composites can be improved to some extent. The thermal conductivity can reach 0.89 W/m K for the composite with 33.3 vol % MWNT‐g‐SMA, which was four times higher than that of neat PS. A linear increase of the thermal conductivity was observed with increasing MWNTs‐g‐SMA content, and the Maxwell–Eucken model and the Agari model were used for theoretical evaluation. Compared with MWNT‐OH, MWNT‐g‐SMA with larger diameter exhibited diffused boundary with the PS matrix, resulting from the strong interfacial bonding of the two phases. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fabrication of multiwalled carbon nanotubes with polymer shells through surface RAFT polymerization

A core–shell hybrid nanostructure, possessing a hard backbone of multiwalled carbon nanotubes (MWNTs) and a soft shell of brush‐like poly(methyl methacrylate), has been successfully prepared via a reversible addition–fragmentation chain transfer (RAFT) process using a RAFT agent immobilized on MWNTs. Polymer‐modified MWNTs are easily dispersed in good solvents for the grafted polymer, such as toluene, tetrahydrofuran and CHCl₃. This observation has been confirmed by transmission electron microscopy analysis. The content of polymer in the functionalized MWNTs can be well controlled by the feed ratio. It is believed that realizing these hybrid structures, on the basis of such simple grafting, will pave the way for the design, fabrication, optimization and eventual application of more functional carbon nanotube‐related nanomaterials. Copyright © 2007 Society of Chemical Industry     

Functionalizing carbon nanotubes by grafting cyclotriphosphazene derivative to improve both mechanical strength and flame retardancy

An intumescent flame‐retardant, hex(4‐carboxylphenoxy) cyclotriphosphazene (HCPCP) was synthesized and covalently grafted on to the surface of multiwalled carbon nanotubes (MWNTs) to obtain MWNT‐HCPCP. MWNT/epoxy resin (EP) and MWNT‐HCPCP/ EP nanocomposites were prepared via thermal curing. Transmission electron microscopy results showed that a core–shell structure with MWNTs as the hard core and HCPCP as the soft shell were formed after HCPCP (10 wt%) were attached to the MWNTs. The results of flammability tests showed an increased limited oxygen index value for MWNT‐HCPCP/EP nanocomposites. The mechanical properties including tensile strength and elongation were both dramatically improved due to the better dispersion of MWNT‐HCPCP in the EP matrix. The grafting of HCPCP can improve both the dispersion of nanotubes in polymer matrix and flame retardancy of the nanocomposites. POLYM. COMPOS., 35:2187–2193, 2014. © 2014 Society of Plastics Engineers     

RGD-conjugated silica-coated gold nanorods on the surface of carbon nanotubes for targeted photoacoustic imaging of gastric cancer

Herein, we reported for the first time that RGD-conjugated silica-coated gold nanorods on the surface of multiwalled carbon nanotubes were successfully used for targeted photoacoustic imaging of in vivo gastric cancer cells. A simple strategy was used to attach covalently silica-coated gold nanorods (sGNRs) onto the surface of multiwalled carbon nanotubes (MWNTs) to fabricate a hybrid nanostructure. The cross-linked reaction occurred through the combination of carboxyl groups on the MWNTs and the amino group on the surface of sGNRs modified with a silane coupling agent. RGD peptides were conjugated with the sGNR/MWNT nanostructure; resultant RGD-conjugated sGNR/MWNT probes were investigated for their influences on viability of MGC803 and GES-1 cells. The nude mice models loaded with gastric cancer cells were prepared, the RGD-conjugated sGNR/MWNT probes were injected into gastric cancer-bearing nude mice models via the tail vein, and the nude mice were observed by an optoacoustic imaging system. Results showed that RGD-conjugated sGNR/MWNT probes showed good water solubility and low cellular toxicity, could target in vivo gastric cancer cells, and obtained strong photoacoustic imaging in the nude model. RGD-conjugated sGNR/MWNT probes will own great potential in applications such as targeted photoacoustic imaging and photothermal therapy in the near future.     

Multiwalled carbon nanotube polymer composites: Synthesis and characterization of thin films

The aim of this article was to elucidate the basic relationships between processing conditions and the mechanical and electrical properties of multiwalled carbon nanotube reinforced polymer composites. In conventional chopped fiber reinforced polymer composites, uniform distributions of fibers throughout the matrix are critical to producing materials with superior physical properties. Previous methods have dispersed carbon nanotubes by aggressive chemical modification of the nanotubes or by the use of a surfactant prior to dispersion. 1 , 2 Here, ultrasonic energy was used to uniformly disperse multiwalled nanotubes (MWNTs) in solutions and to incorporate them into composites without chemical pretreatment. Polystyrene (PS) solutions containing MWNTs were cast and spun to yield thin film MWNT composites. The rheology of PS/MWNT suspensions was modeled using the Carreau equation. MWNTs were found to align at the shear rates generated by the spin casting process. The tensile modulus and strain to failure of samples compared well to classical micromechanical models, increasing with MWNT loading. The composite films showed lower strains at the yield stress than neat PS films. The presence of MWNTs at 2.5 vol % fraction approximately doubles the tensile modulus, and transforms the film from insulating to conductive (surface resistivity, ρ, approaching 10³ Ω/□). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2660–2669, 2002     

Grafting polystyrene onto silica nanoparticles via RAFT polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to graft polystyrene (PS) onto silica nanoparticles. A novel route was used to prepare the RAFT agent, 2-butyric acid dithiobenzoate (BDB) by substitution of dithiobenzoate magnesium bromide with sodium 2-bromobutyrate under alkali condition in aqueous solution. Epoxy groups were covalently attached to silica nanoparticles by condensation reaction of 3-glycidyloxypropyltrimethoxysilane (GPS) with the hydroxyl on the silica particle surface. RAFT agent functionalized nanoparticles were produced by ring-open reaction of the epoxy group with the carboxyl group of BDB. Then, PS chains with controlled molecular weights and narrow polydispersities (less than 1.1) were grown from the RAFT agent anchored nanoparticle surface. FT-IR, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) results showed that PS chains grew from silica particles by surface RAFT polymerization.     

Effects of functionalized MWNTs with GMA on the properties of PMMA nanocomposites

The acid modification of multiwall carbon nanotubes (MWNTs) was performed by an HNO₃/H₂SO₄ solution. The glycidyl methacrylate (GMA) undergoing an opening‐ring was grafted onto the surface of acid‐modified MWNTs. The surface properties of MWNTs were investigated by Fourier transform infrared spectrometer (FTIR), Raman spectra, transmission electron microscopy (TEM), X‐ray diffraction, and thermogravimeric analysis. Then the MWNTs/ poly(methyl methacrylate) (PMMA) nanocomposites were prepared by in situ polymerization. The tribological and dielectric properties of nanocomposites were studied. As a result, GMA was grafted on the surface of MWNTs. The tribological and dielectric properties of MWNTs/ PMMA nanocomposites were improved as the content of the surface‐modified MWNT increased. The marked improvement in tribological and dielectric properties were attributed to the good dispersion of MWNTs that were bonded with C?C on the surface that participated in the polymerization of MMA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication of conducting polyaniline–multiwalled carbon nanotube nanocomposites and their use as templates for loading gold nanoparticles

A new and effective route to synthesize conducting polyaniline‐multiwalled carbon nanotube (PANI ‐f‐MWNT) nanocomposites (where ‘f’ denotes that the MWNTs have been functionalized) starting with amine‐protected 4‐aminophenol is reported. Aminophenol‐functionalized MWNTs were initially synthesized by functionalizing acyl chloride‐terminated nanotubes with N‐(tert‐butoxycarbonyl)‐4‐aminophenol followed by the in situ chemical oxidative grafting of aniline in the presence of ammonium persulfate as an oxidizing agent. Control of the morphology and thickness of the polymer–MWNT nanocomposites was achieved by varying the weight ratios of aniline monomers and MWNTs in the polymerization process. Fourier transform infrared spectroscopy was employed to characterize the initial changes in surface functionalities which also confirmed that PANI was covalently grafted to the MWNTs. Electron microscopy and UV‐visible absorption spectroscopy were employed to characterize the morphology and chemical structure of the resulting hybrids. The results obtained indicate that the structure of the MWNTs was not perturbed by the incorporation of PANI. The content of the polymer in the nanocomposites was determined thermogravimetrically, while the electrical conductivity was obtained using four‐probe measurements. The PANI ‐f‐MWNT nanocomposites were adopted as templates for further decoration with gold nanoparticles in solution, thus opening new possibilities for their prospective technological applications. Copyright © 2010 Society of Chemical Industry     

Grafting of polystyrene and poly(p‐chlorostyrene) from the surface of ramie fiber via RAFT polymerization

Reversible addition‐fragmentation chain transfer (RAFT) radical polymerization was used for controlled grafting of styrene and p‐chlorostyrene from the surface of ramie fiber. The hydroxyl groups in ramie fiber were first converted to thiocarbonylthio groups as the RAFT chain transfer agent then used to mediate the RAFT polymerization of styrene, and p‐chlorostyrene in tetrahydrofuran using azobis (isobutyronitrile) as initiator at 60°C. The grafted copolymers were analyzed by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry, and contact angle measurements. The results confirmed that grafting occurred on the surface of the ramie fiber, substantially increasing the water contact angle from 75.31° to 147° for polystyrene grafted ramie fiber (cell‐PS) and 135° for poly(p‐chlorostyrene) (cell‐PSCl), and improving the hydrophobicity of the grafted fiber. The homopolymers formed in the polymerization were analyzed by size exclusion chromatography to estimate the molecular weights and polydispersity indices (PDIs) of chains grafted from the surface of the ramie fiber, as well as showed narrow chain length distributions with a PDI of 1.32–1.70. These materials possess potential applications in many advanced technologies. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of alkylated carbon nanotube/polyimide nanocomposites

BACKGROUND: The development of carbon nanotube‐reinforced composites has been impeded by the difficult dispersion of the nanotubes in polymers and the weak interaction between the nanofiller and matrices. Efficient dispersion of carbon nanotubes is essential for the formation of a functional nanotube network in a composite matrix. RESULTS: Multiwalled carbon nanotubes (MWNTs) were incorporated into a polyimide matrix to produce MWNT/polyimide nanocomposites. To disperse well the MWNTs in the matrix and thus improve the interfacial adhesion between the nanotubes and the polymer, ‘branches’ were grafted onto the surface of the nanotubes by reacting octadecyl isocyanate with carboxylated MWNTs. The functionalized MWNTs were suspended in a precursor solution, and the dispersion was cast, followed by drying and imidization to obtain MWNT/polyimide nanocomposites. CONCLUSION: The functionalized MWNTs appear as a homogeneous dispersion in the polymer matrix. The thermal stability and the mechanical properties are greatly improved, which is attributed to the strong interactions between the functionalized MWNTs and the polyimide matrix. Copyright © 2009 Society of Chemical Industry     

Poly(2‐(methacryloyloxy) ethyl phosphorylcholine)‐functionalized multi‐walled carbon nanotubes: Preparation,characterization, solubility,and effects on blood coagulation

Water‐soluble multi‐walled carbon nanotubes (MWNTs) were prepared via surface‐initiated atom transfer radical polymerization (ATRP) of 2‐(methacryloyloxy) ethyl phosphorylcholine (MPC) from carbon nanotubes (CNTs). The success of the surface functionalization of MWNTs with poly(2‐(methacryloyloxy) ethyl phosphorylcholine) (pMPC) was ascertained using fourier transform infrared spectrophotometry (FTIR), thermogravimetric analysis (TGA), hydrogen nuclear magnetic resonance (¹H‐NMR), and transmission electron microscopy (TEM). Different from the results of the previous work, in our work, we demonstrate that the amount of pMPC on CNTs can be easily regulated by ATRP approach. In addition, from TGA results, a linear relationship between the weight loss fraction of MWNT‐pMPC and the weight of MPC fed and as high as 48.1% weight loss of MWNT‐pMPC (MWNTs grafted by pMPC) are observed. Through TEM, the core‐shell structure of MWNT‐pMPC is clearly observed, which is also different from the previous report. The pMPC‐modified MWNTs are highly soluble, which can also resist pH and saline concentration changes and remain stable in physiological environment. PMPC‐modified MWNT does not significantly affect the blood coagulation as demonstrated in plasma recalcification time (PRT) test. These highly soluble MWNTs are expected to enable their wide use in biomedical areas. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Enhanced interactions between multi-walled carbon nanotubes and polystyrene induced by melt mixing

The effect of melt mixing on the interaction between multi-walled carbon nanotubes (MWNTs) and polystyrene (PS) matrix has been investigated. The interaction between pristine MWNTs and PS in solution was found to exist but not strong enough to allow MWNTs to be soluble in solvent. In contrast, this interaction between MWNTs and PS was significantly enhanced by melt mixing, which led to increased amount of PS-functionalized MWNT exhibiting good solubility in some solvents. The mechanism of melt mixing on this enhanced interaction was attributed to both chemical bonding and physical interaction during the melt mixing.     

Synthesis of graphene-polystyrene nanocomposites via RAFT polymerization

Synthesis of graphene-polymer nanocomposites is of current interest due to their exceptionally physical and chemical properties. However, the ability to produce conductive inks/coatings retaining the properties of the graphene is still a major challenge. In this study, functionalized polydopamine-coated reduced graphene oxide (PDA/RGO) was reacted with a RAFT agent, 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT), to form macro-RAFT agents via an esterification reaction. The chemistry and kinetics of RAFT living/controlled polymerization of styrene was examined from the surface of these macro-RAFT agents to form polystyrene-grafted PDA/RGO (PS-g-PDA/RGO). By examination of the kinetics and GPC traces of the free and grafted polymer, living/controlled polymerization was confirmed. To examine the utility of this approach, the synthesized PS-g-PDA/RGO samples containing different amounts of grafted PS were employed in the preparation of graphene-PS nanocomposites by mixing them with commercial PS. Graphene was found to be well distributed in the PS matrix by this approach, increasing the decomposition temperature range. This research provides an efficient route towards the design and development of value-added functional graphene-PS composites.     

A mesoporous composite template composed of self-assembled silica nanotube and multi-walled carbon nanotube

The multi-walled carbon nanotubes (MWNTs) were successfully embedded in the hexagonally-arranged silica tubular structure by the self-organization of two surfactant systems providing a MWNT-incorporated silica nancomposite template. The anionic surfactant (sodium dodecyl sulfate, SDS) adsorbed on the MWNT surfaces allowed the MWNTs to interact with the outer surface of the self-assembled non-ionic surfactant, poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer. Due to the hydrophilic–hydrophilic interaction between the PEO blocks and the sulfate group of SDS, the MWNTs were most possibly surrounded by the outer wall of the SBA-15 hexagonal tubes aligning in the longitudinal and transverse directions to the silica tube direction. According to the interplanar distances, electron microscopy images, and N₂ adsorption–desorption isotherms, the synthesized SBA-15/MWNT system exhibited the structural integrity of silica-tube arrangement and structural characteristics of MWNTs in terms of BET surface area and micropore volume. This work made it clear that the developed SBA-15/MWNT template could be used to synthesize various MWNT-incorporated 2-D replicas.     

Polyelectrolyte-functionalized multiwalled carbon nanotubes: preparation, characterization and layer-by-layer self-assembly

Two kinds of polyelectrolyte: polyacrylic acid (PAA) and poly(sodium 4-styrenesulfonate) (PSS), were grafted onto the convex surfaces of multiwalled carbon nanotubes (MWNTs) by surface-initiating ATRP (atom transfer radical polymerization) from the initiating sites previously anchored onto the convex surfaces of MWNTs. The grafted polyelectrolyte can be efficiently quantified by the feed ratio of monomer to MWNT-based macroinitiator, and the maximum amount of grafted polymer is higher than 55 wt%. The polyelectrolyte-coated MWNTs resembled core-shell structures justified by the TEM images of the samples obtained, which provided direct evidence for the covalent modification of MWNT. FTIR, ¹H NMR and TGA were used to determine the chemical structure of the resulting products. Comparison of UV-Vis spectra demonstrated that the products were water-soluble, and that PSS was more effective for improving the water solubility of carbon nanotubes. Using the polyelectrolyte- and carboxylic acid-functionalized MWNTs as templates, and poly(2-(N,N-dimethylaminoethyl) methacrylate (PDMAEMA)/hyperbranched polysulfone amine (HPSA) and PSS as polycation and polyanion, respectively, layer-by-layer (LbL) electrostatic self-assembly was conducted in order to explore the application of the functionalized nanotubes. It was found that the functionalized MWNTs have a high efficiency for loading polyelectrolytes by the LbL approach (the adsorbed polymer quantity is higher than 10 wt% in one assembling step). TEM observations showed that the assembled polymer shell on the MWNT surfaces was very even and flat.