Noncovalent functionalization of carbon nanotubes with maleimide polymers applicable to high-melting polymer-based composites

As novel carbon nanotube (CNT) dispersants are effective not only for obtaining stable CNT-dispersed solutions but also for high-melting polymer/CNT composites, we synthesized maleimide polymers (MIPs) using N-substituted maleimide for imparting physical adsorption on the CNT surfaces and high heat resistance. The MIPs showed strong physical adsorption on various CNT surfaces and good solubility in a wide variety of organic solvents, and acted as excellent CNT dispersants in these substances. The MIPs on the CNT surfaces were very stable at high temperatures (?∼300 °C) required for melt mixing using high-melting polymers. The addition of MIP-adsorbed CNTs (CNT/MIPs) to poly(1,4-phenylenesulfide) (PPS) as a high-melting polymer was, therefore, very effective for dispersing CNTs and improving the physical properties of the resulting PPS/CNT/MIP composites, in comparison with the PPS/CNT composites. Even at a low CNT loading (1 vol%), the storage modulus of the PPS/CNT/MIP composites increased drastically. Furthermore, thermal conductivity of the PPS/CNT/MIP composites also improved, in comparison with the PPS/CNT composites. These results are considered to be due to an increase of interactions between the CNT and PPS matrices, caused by the stable formation of MIPs on the CNT surfaces.     

UHMWPE/CNTs冻胶体系的流变行为研究

研究了碳纳米管(CNTs)的加入对超高分子质量聚乙烯(UHMWPE)稳态表观粘度、粘流活化能、非牛顿指数和结构粘度指数的影响。结果表明:碳纳米管添加量小于或等于3ω时,UHMWPE/CNTs冻胶体系的粘流括化能降低,表观粘度都低于空白UHMWPE冻胶体系。CNTs的加入对UHMWPE冻胶体系的非牛顿指数和结构粘度指数影响不大。     

Influence of molecular weight and molecular weight distribution on the tensile properties of amorphous polymers

Tensile property data for polystyrene samples of varying polydispersity are correlated with various parametric measures of molecular weight. Traditional measures of molecular weight, such as M?_n, M?_w, and M?_z, are shown to be unable to account for the variation of tensile properties with molecular weight. However, a new molecular weight parameter, termed the failure property parameter, is able to provide a single relationship between tensile strength and the parameter for both the broad and narrow distribution polymers. The form of this parameter is consistent with its having origins in the view that it is the entanglement network in an amorphous polymer that provides the observed strength properties. Specifically for polystyrene, the failure property parameter results indicate that material below 60,000 molecular weight does not contribute to polymer strength. Although the results of this investigation are specifically for polystyrene, the arguments used to develop the failure property parameter are not dependent on polymer chemical structure. Consequently, we believe that both the concepts and definition of this new parameter are applicable to all amorphous polymers.     

Toughening high performance ultrahigh molecular weight polyethylene using multiwalled carbon nanotubes

We report experimental observations on the drastically enhanced toughness in the high-strength and high-modulus ultrahigh molecular weight polyethylene (UHMWPE) films due to the addition of 1 wt% multiwalled carbon nanotubes (MWCNTs). A combination of tensile and Raman spectroscopic measurements showed that the presence of MWCNTs in the composites can lead to a ∼150% increase in strain energy density in comparison with the pure UHMWPE film at similar draw ratios. This is accompanied with an increase of ∼140% in ductility and up to 25% in tensile strength. We attribute the above observations to the chain mobility enhancement in UHMWPE induced by the MWCNTs.     

Influence of chemical functionalization of carbon nanotubes on their dispersibility in alkyl methacrylate polymer matrix

Nanocomposites based on poly(methyl methacrylate) (PMMA) and poly(methyl methacrylate‐co‐octadecyl methacrylate) (M/O) matrices and four different types of multiwall carbon nanotubes: pristine, oxidized (MWCNT–COOH), methyl ester (MWCNT–COOCH₃), and dodecyl ester (MWCNT–COOC₁₂H₂₅) functionalized, were prepared in situ by radical (co)polymerization. The effectiveness of preparation of nanocomposites regarding dispersion and distribution of various MWCNT in polymer matrices was sized by Scanning electron microscopy. In case of PMMA matrix, the best dispersion and distribution were accomplished for MWCNT–COOCH₃ due to their chemical resemblance with polymer matrix. After the introduction of 10 mol % of octadecyl methacrylate in polymer matrix a fairly good dispersion and distribution of MWCNT–COOCH₃ were retained. The addition of 1 wt % of MWCNTs caused a significant reduction in the degree of polymerization of the PMMA matrix. But at the same time, the present MWCNTs increased storage modulus of PMMA nanocomposites except for dodecyl ester functionalized MWCNT. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46113.     

Viscometric determination of the molecular weight of polymers in the low molecular weight region

In order to overcome the difficulty of the determination of the molecular weight of a polymer in the low molecular weight region by viscometry using the Mark–Houwink–Sakurada (MHS) equation, we have proposed the Dondos–Benoit relationship [η]^?1 = A₂ + AM^?1/2, for a number of polymer–solvent systems, for which we give the numerical values of the parameters A₁ and A₂. Furthermore, we suggest a method for the determination of the above parameters using the MHS constants a and k.     

Investigation of molecular interaction between single‐walled carbon nanotubes and conjugated polymers

Single‐walled carbon nanotubes (SWNTs) have unique properties such as high electrical conductivity and high tensile strength. Their composites with polymers have a great role in new sciences such as organic solar cells and ultrastrong lightweight materials. In this article, molecular dynamic simulations with polymer consistent force field are performed to study the interaction between SWNTs and conjugated polymers including poly(2‐methoxy‐5‐(3‐7‐dimethyloctyloxy)‐1,4‐phenylenevinylene) (MDMO‐PPV), poly(3‐hexythiophene) (P3HT), and poly[(9,9′‐dioctylfluorenyl‐2,7‐diyl)‐co‐bis(N,N′‐(4,butylphenyl))bis(N,N′‐phenyl‐1,4‐phenylene)diamine] (PFB). We computed the interaction energy and morphology of polymers adsorbed to the surface of SWNTs was studied by the radius of gyration (Rg). The influence of important factors such as SWNT radius, chirality, and the temperature on the interfacial adhesion of SWNT–polymer and Rg of polymers were studied. We found that the strongest interaction between the SWNTs and these polymers was, first observed for P3HT, then MDMO‐PPV, and finally PFB. Our results showed that the interaction energy is influenced by SWNT radius and the specific monomer structure of the polymers, but the effects of chirality and temperature are very weak. In addition, we found that the temperature, chirality, and radius have not any important effect on the radius of gyration. POLYM. COMPOS.,, 2012. © 2012 Society of Plastics Engineers     

UHMWPE/CNTs复合纤维的结晶行为研究

分别用DSC、X衍射、热台偏光显微镜对超高分子质量聚乙烯（UHMWPE）和UHMWPE／CNTs（碳纳米管）复合纤维的结晶行为进行了研究。结果表明：碳纳米管的加入使得复合材料的熔点较UHMWPE有所提高,碳纳米管起到了成核剂的作用。晶片厚度较UHMWPE增加。     

Preparation and characterization of water-based concentrated carbon nanotubes slurry with high dispersibility and stability

In order to apply the excellent properties of carbon nanotubes to the field of biomedicine, water-based high concentration carbon nanotubes(CNTs) slurry with high dispersibility and stability was prepared by adjusting illumination conditions and pH values. The infrared spectroscopy, zeta potential, TEM and digital camera were used to investigate the effect of illumination conditions and pH values on the dispersibility and stability of the CNTs slurry. The results show that the CNTs slurry has more functional groups and can be sufficiently oxidized in the absence of light than in the natural and intense light conditions. And the higher light intensity used for oxidation treatment caused a decrease of the functional groups and the surface activity of the CNTs in the slurry. The increase of the pH value can promote electrostatic repulsion, and the enhancement of light intensity can decrease the electrostatic repulsion. So, the CNTs individuals oxidized in the absence of light possessed high dispersibility and stability as varying pH value from 11.5 to 4, which slurry concentration is 10 wt% and no CNTs settlement was observed for nearly one year. However, the CNTs in the water-based carbon nanotube slurry prepared under other illumination conditions re-agglomerated and settled after several days, especially when the pH value is below 4.     

Shear-controlled electrical conductivity of carbon nanotubes networks suspended in low and high molecular weight liquids

Controlling the electrical conductivity is a critical issue when processing material systems consisting of an insulating matrix filled with conductive particles. We provide experimental evidence that given shear rates result in specific conductivity levels in such different systems as high-viscosity carbon nanotube/polymer melt or low-viscosity carbon nanotube/epoxy fiber suspensions. The steady-state conductivities are independent of the initial state of the dispersion. The observed behavior is modeled phenomenologically by the competition between build-up and destruction of conductive filler network. A particle-level simulation of flowing fiber suspension also reflects the observed behavior. Our results show that properties of particulate suspensions can be controlled by steady shear. They should be considered to obtain reproducible properties in shear-based processing technologies as injection molding or resin transfer molding.     

Functionalization of multi-walled carbon nanotubes with furan and maleimide compounds through Diels-Alder cycloaddition

Functionalization of multi-walled carbon nanotubes (MWCNTs) is performed through Diels-Alder (DA) reaction, using either furfuryl alcohol (a diene) or N-(4-hydroxyphenyl)maleimide (NHMI, a dienophile) as a functionalization agent. The structures of the functionalized MWCNTs are characterized with Fourier-transform infrared spectroscopy and Raman spectroscopy. Thermogravimetric analysis results also demonstrate the presence of organic portions of the functionalized MWCNTs. The DA reaction is further applied to incorporate polymer chains onto MWCNT surfaces, using a polyamide with maleimide pendent groups. Transmission electron microscopy images show the presence of a polymer layer of about 2-5 nm around the polymer modified MWCNTs.     

Effects of molecular weight,stereo configuration of PLA,and processing on the dispersion of multiwalled carbon nanotubes and properties of corresponding nanocomposites

Multiwalled carbon nanotubes (MWCNTs) were dispersed and distributed via a co-rotating twin-screw extruder (TSE) in high (h)- and low (l)-molecular-weight amorphous and semicrystalline polylactides (PLAs) (aPLA and scPLA, respectively). Effects of PLA molecular weight and D-lactic acid equivalents content (D-content), as well as processing parameters, were examined on the MWCNT dispersion quality in PLA. The effectiveness of the MWCNT dispersion in various PLA matrices was investigated using scanning electron microscopy (SEM) and small-amplitude oscillatory and transient shear flow rheometry in the molten state. The results showed a better dispersion of MWCNTs in the low-molecular-weight PLA grades (aPLAl and scPLAl). In addition, better MWCNT dispersion was observed in aPLA grades when processed at a higher temperature of 190°C than at 150°C. At 150°C, while MWCNT bundles in aPLAl could be broken down, a good dispersion could not be achieved in aPLAh due to the lower molecular mobility at such a temperature. The electrical conductivity of the samples was also shown to increase as the MWCNT dispersion was improved. The existence of crystallites in scPLA-based nanocomposites, however, disrupted the connectivity of the MWCNTs and decreased the final electrical conductivity. The lower molecular weight aPLAl prepared at 190°C showed the highest electrical conductivity (~10⁻⁵ S/m) at a low loading of 0.5 wt.% MWCNTs.     

Composites based on acrylic polymers and carbon nanotubes as precursors of carbon materials

The effect of carbon nanotubes on the properties of composite fibers and films based on polyacrylonitrile is analyzed. It is shown that the introduction of carbon nanotubes makes it possible to improve the mechanical characteristics of the composite material. Data on the effect of carbon nanotubes on chemical reactions occurring during the thermal stabilization and carbonization of these materials are cited.     

Viscosity—molecular weight relationship for cellulose tripropionate in chloroform

The hitherto unreported constants in the Mark-Houwink viscosity-molecular weight relationship have been determined for both number-average and weight-average molecular weights for cellulose tripropionate in chloroform. Five narrow molecular weight range samples of a prepared cellulose tripropionate were obtained by fractional precipitation and characterized by osmometric and g.p.c. measurements. The cellulose tripropionate chain showed a high rigidity, characteristic of cellulosic polymers, but appeared to be more flexible than the corresponding triacetate in the same solvent.     

Non-covalent interactions between carbon nanotubes and conjugated polymers

Carbon nanotubes (CNTs) are interest to many different disciplines including chemistry, physics, biology, material science and engineering because of their unique properties and potential applications in various areas spanning from optoelectronics to biotechnology. However, one of the drawbacks associated with these materials is their insolubility which limits their wide accessibility for many applications. Various approaches have been adopted to circumvent this problem including modification of carbon nanotube surfaces by non-covalent and covalent attachments of solubilizing groups. Covalent approach modification may alter the intrinsic properties of carbon nanotubes and, in turn make them undesirable for many applications. On the other hand, a non-covalent approach helps to improve the solubility of CNTs while preserving their intrinsic properties. Among many non-covalent modifiers of CNTs, conjugated polymers are receiving increasing attention and highly appealing because of a number of reasons. To this end, the aim of this feature article is to review the recent results on the conjugated polymer-based non-covalent functionalization of CNTs with an emphasis on the effect of conjugated polymers in the dispersibility/solubility, optical, thermal and mechanical properties of carbon nanotubes as well as their usage in the purification and isolation of a specific single-walled nanotube from the mixture of the various tubes.     

Potentiometric determination of the molecular weight of polymers

Summary The determination of acid end-groups of acrylamide and acrylonitrile polymers initiated by cerium (IV)-malonic acid, cerium (IV)-tartaric acid and cerium (IV)-citric acid redox initiators systems was made in aqueous and nonaqueous media potentiometrically. The effect of solvent, titrant and electrode system on the half-neutralization potentials and number-average molecular weights, , were determined potentiometrically and were studied. These values were compared with those obtained by viscosimetric and conductometric methods.     

Effects of bimetallic catalyst composition and growth parameters on the growth density and diameter of carbon nanotubes

Multi-wall carbon nanotubes (MWNTs) were synthesized by catalytic decomposition of acetylene over Fe, Ni and Fe-Ni bimetallic catalysts supported on alumina under various controlled conditions. The growth density and diameter of CNTs were markedly dependent on the activation time of catalysts in H₂ atmosphere, reaction time, reaction temperature, flow rate of acetylene, and catalyst composition. Bimetallic catalysts were apt to produce narrower diameter of CNTs than single metal catalysts. For the growth of CNTs at 600 ‡C under 10/100 seem flow of C₂H₂/H₂ mixture, the narrowest diameter about 20 nm was observed at the reaction time of 1 h for 20Fe : 20Ni : 60Al₂O₃ catalyst, but at that of 1.5 h for 10Fe : 30Ni : 60Al₂O₃ catalyst. It was considered that the diameter and density of CNTs decreased with the increase of the growth time mainly due to hydrogen etching. The growth of CNTs followed the tip growth mode.