Polymer adsorption in the grafting reactions of hydroxyl terminal polymers with multi-walled carbon nanotubes

Melt stirring of non-functional polymers such as poly(ethylene oxide) dimethylether (PEO-Me) and polystyrene (PS-H) with multiwalled carbon nanotubes (MWNTs) in the absence of solvent for 48 h induced a substantial amount of polymer adsorption on the MWNTs. The chloroform extraction of the reaction products using centrifugation yielded black colored solutions exhibiting UV absorbance corresponding to the presence of MWNTs. The adsorption of polymer was confirmed on the surfaces of solvent washed residual and recovered MWNTs from the reactions using thermogravimetric analysis (TGA) and FT-IR spectroscopy. Covalent grafting reactions carried out using hydroxyl-terminated PEO-OH and PS-OH with acid chloride containing MWNTs under identical melt stirring condition produced similar results. The presence of polymer on the residual and recovered MWNTs irrespective of the nature of the terminal groups indicates that the adsorption of polymers poses a problem in accurately determining the grafting efficiency. FT IR spectra of the PEO-g-MWNTs shows a substantial shift in CH stretching vibrations indicating a plausible weak intermolecular interaction with π electrons of the MWNTs.     

A facile gemini surfactant-improved dispersion of carbon nanotubes in polystyrene

Debundling and dispersion of carbon nanotubes (CNTs) are very important for preparation of polymer/CNT nanocomposites. In the present study, a self-prepared gemini surfactant, 6,6′-(butane-1,4-diylbis(oxy))bis(3-nonylbenzenesulfonic acid), is employed to achieve homogeneous and stable dispersion of multi-walled carbon nanotubes (MWNTs) in organic solvent and subsequent polystyrene (PS)/MWNT nanocomposite. Sedimentation, optical microscopy and transmission electron microscopy studies demonstrate that the gemini surfactant can greatly improve the dispersion and stabilization of MWNTs in toluene. Scanning electron microscopic images clearly confirm the homogenous dispersion of individual MWNTs in PS. In addition, desired enhanced electrical conductivity and thermal stability of the nanocomposite relative to those of the neat PS are obtained.     

Asymmetric Flexible Supercapacitor Stack

Electrical double layer supercapacitor is very significant in the field of electrical energy storage which can be the solution for the current revolution in the electronic devices like mobile phones, camera flashes which needs flexible and miniaturized energy storage device with all non-aqueous components. The multiwalled carbon nanotubes (MWNTs) have been synthesized by catalytic chemical vapor deposition technique over hydrogen decrepitated Mischmetal (Mm) based AB₃ alloy hydride. The polymer dispersed MWNTs have been obtained by insitu polymerization and the metal oxide/MWNTs were synthesized by sol-gel method. Morphological characterizations of polymer dispersed MWNTs have been carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM and HRTEM). An assymetric double supercapacitor stack has been fabricated using polymer/MWNTs and metal oxide/MWNTs coated over flexible carbon fabric as electrodes and nafion^® membrane as a solid electrolyte. Electrochemical performance of the supercapacitor stack has been investigated using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy.     

Effects of aspect ratio of MWNT on the flammability properties of polymer nanocomposites

The effects of the aspect ratio of multi-walled carbon nanotubes (MWNTs) on the rheology and flammability of polystyrene/MWNT nanocomposites are studied using two MWNTs having average aspect ratios (length to outer diameter) of 49 and 150. Dynamic rheological experiments show that the particles with the larger aspect ratio impart much higher storage moduli and complex viscosities to the nanocomposites compared to equivalent mass loadings of particles with the smaller aspect ratio. Additionally, in flammability experiments, the larger aspect ratio particles lead to a greater reduction in mass loss rate, i.e., they are more effective at reducing flammability. These results demonstrate that the aspect ratio of MWNTs is a key parameter in controlling the rheology and flammability of polymer nanocomposites.     

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.     

A novel route for well‐defined polystyrene‐grafted multiwalled carbon nanotubes via the radical coupling reaction

Multiwalled carbon nanotubes‐graft‐polystyrene (MWNTs‐g‐PS) was synthesized by atom transfer nitroxide radical coupling chemistry. MWNTs with 2,2,6,6‐tetramethylpiperidine‐1‐oxy (MWNTs‐TEMPO) groups was prepared first by esterification of 4‐hydroxy (HO)‐TEMPO and carboxylic acid group on the surface of MWNTs (MWNTs‐COOH); PS with bromide end group (PS‐Br) were then obtained by atom transfer radical polymerization using ethyl 2‐bromoisobutyrate as initiator and CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as catalyst. The MWNTs‐TEMPO was mixed with PS‐Br and heated to 90°C in the presence of CuBr/PMDETA to form MWNTs‐g‐PS. The product was characterized by FTIR, NMR, TGA, and TEM. TEM indicates that the MWNTs are enveloped by the polymer molecules. The content of grafted polymers is 46.7% by TGA measurements when the number‐average molecular weight (M_n) of PS‐Br is 10,200 g/mol. The as‐prepared nanocomposites exhibit relatively good dispersibility in solvents such as CH₂Cl₂, THF, and toluene. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Functionalization of multiwalled carbon nanotubes with amphiphilic poly(aspartic acid)

A new method to functionalize multiwalled carbon nanotubes (MWNTs) with amphiphilic poly(aspartic acid) was investigated. The amphiphilic polymer (PASP‐C16) was synthesized by thermal condensation and aminolysis by hexadecylamine, followed by hydrolysis of the remaining succinimide units in the polymer backbone. The functionalization of MWNTs was achieved by physical adsorption of the biopolymer onto the surfaces of MWNTs. Ultraviolet‐visible ( UV‐vis) spectra showed that the functionalized MWNTs had a good aqueous dispersity and solubility. The interaction of PASP‐C16 with MWNTs was investigated by analyzing X‐ray diffraction (XRD) patterns, circular dichroism (CD), spectra and high‐resolution transmission electron microscopy ( HRTEM ). From the XRD patterns, it can be known that the aggregate of PASP‐C16 due to intermolecular interaction between hexadecyl chains has been reduced when the polymer interacting with MWNTs. CD spectra indicated that the interaction of hexadecyl chains of PASP‐C16 with the wall of MWNTs is the major interaction between PASP‐C16 and MWNTs, and MWNTs were covered by the poly(aspatic acid) backbone. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

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     

On the influence of the processing conditions on the performance of electrically conductive carbon nanotube/polymer nanocomposites

We prepared multiwalled carbon nanotube/polystyrene (MWCNT/PS) nanocomposites using a latex-based process, the main step of which consists of directly mixing an aqueous suspension of exfoliated MWCNTs and a PS latex, both stabilized by an anionic surfactant. After freeze drying and compression molding homogeneous polymer films with well-dispersed carbon nanotubes were produced as evidenced by scanning electron microscopy. Conductivity measurements performed on our nanocomposite films show that they have a low percolation threshold and exhibit high levels of electrical conductivity above this threshold. We observe that both these properties are influenced by the applied processing conditions, i.e., temperature and time, and provide a plausible explanation based on the diffusive motion of the MWNTs in the polymer melt during the compression molding stage.     

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     

Carbon nanotube reinforced rigid‐rod polyimide

Multiwalled carbon nanotube/rigid‐rod polyimide composite films have been prepared by casting a solution of precursor polymer (polyamide acid) containing multiwalled carbon nanotubes (MWNTs) into thin films, followed by a thermal imidization treatment. The composite films were characterized by FTIR, TEM, DSC, TGA and TMA, and the film tensile properties were also examined. The presence of 1.0% MWNTs in the polymer matrix led to more than twofold increase in tensile strength of the rigid‐rod polyimide composite films and improved thermal stability, but reduced in thermal deformation. However, the tensile property did not show further increase when the film contained higher composition of MWNTs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Shear enhanced interfacial interaction between carbon nanotubes and polyethylene and formation of nanohybrid shish-kebabs

In this work, raw multiwalled carbon nanotubes (MWNTs) without any pre-treatment were blended with linear low density polyethylene (LLDPE), then molded via a so-called Dynamic Packing Injection Molding (DPIM) technique, in which oscillatory shear was exerted on the prepared composites during the stage of cooling solidification. The injection molded samples were extracted by xylene to remove LLDPE, and the remained MWNTs were collected and characterized. Shear enhanced interfacial adhesion between MWNTs and LLDPE was confirmed by dissolution experiment and Fourier transform infrared. The former a longer mixing time in xylene for remained MWNTs compared with raw MWNTs, while in the latter an increased intensity of characteristic LLDPE peak for MWNTs subjected to dynamic packing injection molding. More importantly, SEM images showed a formation of MWNTs/LLDPE nanohybrid shish-kebab, in which MWNTs served as shish, and LLDPE lamellae as kebab and periodically decorated on MWNTs. A simultaneously improved tensile strength and elongation of LLDPE have been achieved by adding the LLDPE-decorated MWNTs. Our work provides a new way for the modification of MWNTs, particularly a convenient way for the enhancement of interfacial adhesion in polymer/MWNT composites via realistic molding processing.     

A new approach to functionalize multi-walled carbon nanotubes by the use of functional polymers

A new method to graft a large number of long polymer chains or small functional molecules onto multi-walled carbon nanotubes (MWNTs) indirectly is reported. First, MWNTs were slightly functionalized by reversible addition-fragmentation chain transfer (RAFT) copolymerization of styrene and maleic anhydride using the dithioester groups attached to MWNTs as RAFT agents. The highly reactive maleic anhydride groups could further react with a large number of long polymer chains or small functional molecules with hydroxyl or amino group easily. The resulted MWNTs have good solubility in organic solvents and water; the perfect structure of MWNTs is altered very little from the information of Raman spectra.     

Enhanced dispersion of carbon nanotube in silicone rubber assisted by graphene

We report a novel, scalable and inexpensive approach to fully disperse carbon nanotubes in silicone rubber by the addition of graphene. In comparison to graphene, the dispersion of multi-walled carbon nanotubes (MWNTs) in silicone rubber matrix is extremely difficult although both of them possess similar physical structure. The different dispersion behavior of graphene and MWNTs could be contributed to the difference in their interaction with polymer matrix and their geometry. Based on SEM, TEM and XRD analysis, we find that the dispersion of MWNTs in silicone rubber is dramatically improved by the addition of graphene. Graphene acts as a compatilizer since it shows strong interaction with both polymer matrix and MWNTs. This method provides a simple route to enhance the dispersion of carbon nanotubes and improve the electrical property of the polymer composites. The synergic effect of the hybrid materials may not to be limited to the applications in polymer composites.     

Morphology,crystallization, and mechanical properties of poly(ethylene terephthalate)/multiwall carbon nanotube nanocomposites via in situ polymerization with very low content of multiwall carbon nanotubes

So far, the reported content of multiwall carbon nanotubes (MWNTs) in polymer/MWNTs nanocomposites is usually above 0.1 wt %. In this article, we will report our work on the study of the morphology, crystallization, and mechanical properties of poly(ethylene terephthalate) (PET)/MWNTs nanocomposites prepared by in situ polymerization with very low content of MWNTs (from 0.01 to 0.2 wt %). Well‐dispersed MWNTs with a big network throughout PET matrix were observed by SEM. The very small amount of MWNTs displayed a great nucleating effect on the PET crystallization. The crystallization temperature was improved for 6.4°C by using only 0.01 wt % MWNTs. The decreased chain mobility of PET by adding MWNTs was evident by the formation of imperfect or smaller/thinner crystallites with low melting temperature. An increased storage modulus was also achieved for the nanohybirds with MWNT content less than 0.05 wt %. Our result indicates that using very low content MWNTs (less than 0.1 wt %) is a simple way to achieve good dispersion, yet with remarkable enhancement for polymer/MWNTs modification. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3695–3701, 2007     

Dopamine modification of multiwalled carbon nanotubes and its influences on the thermal,mechanical, and tribological properties of epoxy resin composites

A functionalization process with dopamine on multiwalled carbon nanotubes (MWNTs) has been carried out in order to enhance the tribological properties of MWNTs/epoxy resin (EP) composites. Dopamine modification is of signality for the performance of MWNTs/EP composites. The hardness and flexural strength of the composites were significantly improved with the incorporation of dopamine modified MWNTs, owning to the enhanced interfacial bonding between MWNTs and EP. Meanwhile, the thermal characterizations indicated that dopamine played an important role in improving the thermal stability of MWNTs/EP composites. More importantly, the friction and wear properties of dopamine modified MWNTs/EP composites were enhanced considerably and its wear rate was 85.8% lower than that of pure EP. Dopamine modified MWNTs were linked with the matrix by strong covalent bond to form a great network structure and impeded the movement of polymer molecule chains in the composites. Then the friction load transmitted efficiently through the network structure and the plastic deformation was restrained as well as the initiation and growth of cracks on the worn surfaces. POLYM. COMPOS., 38:116–125, 2017. © 2015 Society of Plastics Engineers     

Efficient dispersion of multi‐walled carbon nanotubes by in situ polymerization

Multi‐walled carbon nanotube (MWNT)‐reinforced polyimide nanocomposites were synthesized by in situ polymerization of monomers in the presence of acylated MWNTs. The acyl groups associated with the MWNTs participated in the reaction through the formation of amide bonds. This process enabled uniform dispersion of MWNT bundles in the polymer matrix. The resultant MWNT–polyimide nanocomposite films were optically transparent with significant mechanical enhancement at a very low loading (0.5 wt%). Evidence has been obtained for improved interactions between the nanotubes and the matrix polymer. Copyright © 2006 Society of Chemical Industry     

In situ synthesis and characterization of poly(2,5-benzoxazole)/multiwalled carbon nanotubes composites

This article reports the synthesis of poly(2,5-benzoxazole)/multiwalled carbon nanotubes (ABPBO/MWNT) composites by in situ polycondensation and their chemical and physical properties. The functional groups yielded from the surface modification of MWNTs by hydrochloric acids have been demonstrated to participate in the polymerization and thus led to the composites with homogenous dispersion of carbon nanotubes. The chemical structures and morphology of the afforded polymer composites have been fully characterized by FTIR, WAXD, UV-vis, TGA and SEM. The ABPBO/MWNT composites exhibit excellent thermal stability and greatly improved mechanical properties. The tensile modulus and tensile strength of the composites are 47% and 83%, respectively, higher than those of the polymer matrix. The dielectric constant of the composites is also significantly enhanced from 4 of the polymer matrix to 65 with the incorporation of 5 wt% MWNTs.     

A Raman Investigation of Carbon Nanotubes Embedded in a Soft Polymeric Matrix

Raman spectroscopy has been used to characterize multiwall carbon nanotubes (MWNTs) styrene-butadiene rubber (SBR) composites. Raman spectra of the MWNTs/SBR composites excited at different excitation wavelengths show that the dependence of the D band of carbon nanotubes on the laser energy has the same behavior as that of pure MWNTs. Raman spectra are shown to be sensitive to the state of dispersion of carbon nanotubes in the polymeric medium. On the other hand, analysis of Raman spectra of uniaxially stretched composites reveals a weak interface between the polymer and the nanotube surface.     

Mechanical,thermal, and rheological behavior of ethylene methyl acrylate‐MWNT nanocomposites

Mechanical, thermal, and rheological properties of ethylene methyl acrylate (EMA) composites reinforced with multiwalled carbon nanotubes (MWNTs) have been reported here. Morphological analyses revealed that MWNTs are more uniformly dispersed in EMA upto 3.5 wt% MWNTs loading. Uniform dispersion of MWNTs in EMA matrix leads to decreased crystallinity and increased crystallite size. These are reflected in the mechanical and thermal properties of the composites. The storage moduli of the composites significantly increase by the incorporation of MWNTs, particularly at higher temperatures. The nanocomposites register a slightly higher viscosity than that of neat EMA depending on the contents of MWNTs. Storage modulus (in dynamic shear) increases especially at higher frequency levels due to increased polymer–filler interactions. Dynamic and steady shear rheological properties register a good correlation in regard to the viscous versus elastic response of the nanocomposites. The morphology correlates well with the dynamic rheological characteristics of these nanocomposites. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers