Polyethylene/carbon nanotube nano hybrid shish-kebab obtained by solvent evaporation and thin-film crystallization

Crystallization of polymers on carbon nanotubes (CNTs) has resulted in a novel nano hybrid shish kebab (NHSK) structure, within which CNTs serve as the nucleation sites (shish) and polymer lamellar crystals form the kebabs. Previously reported NHSK structures were obtained by solution crystallization, bulk crystallization and physical vapor deposition methods. Herein we report a simple, rapid, yet effective approach to produce NHSK materials using solvent evaporation and thin film crystallization. Polyethylene (PE) was used as the model polymer. PE solution was drop cast on CNT-coated carbon films, and upon solvent evaporation, PE crystallized onto/near CNTs, following the template of the latter and NHSK structure was then formed. The final morphology was found to result from the competition between heterogeneous nucleation and homogeneous nucleation of PE. The formation of NHSK also strongly depends on the structure of CNTs as well as the molecular weight of PE. This work shows a facile method to form NHSK and to study CNT-induced crystallization under nonequilibrium conditions.     

聚乙烯-碳纳米管串晶的高效制备(英文)

We report a novel method to prepare nanohybrid shish-kebab (NHSK) structure of polyethylene (PE) and carbon nanotube (CNT). Pristine CNTs without surface modification with high concentration was effectively dispersed in xylene solution by a simple shearing method, which induces the quick crystallization of PE in xylene to form a novel NHSK structure with more dense and smaller PE kebab on CNT axis. The flocculated NHSK product was transferred quickly from the xylene solution to the ethanol solution, in order to shorten the preparation time. The freeze-drying method was used in vacuum instead of high-temperature drying to avoid the aggregation of NHSK product. These improvements allow the formation of NHSK with an absolute yield of 200 mg·h-1 , which is 2000 folds of that reported previously. It is favorable to apply this structured material in high performance nanocomposite, by improving the compatibility of CNTs in polymer and the interfacial force between CNTs and polymer.     

Nanohybrid shish kebab structure and its effect on mechanical properties in poly(L‐lactide)/carbon nanotube nanocomposite fibers

In our previous work, the formation of a nanohybrid shish kebab (NHSK) structure was successfully achieved in helical polymer systems promoted by using single‐walled carbon nanotube (CNT) bundles with a unique ‘groove structure’, which is of great crystallographic interest. To further investigate the effect of surface groove structure of CNT bundles on the formation of NHSK structure in helical polymer systems, in the work reported here double‐walled carbon nanotube (DWNT) fibers with bundle structure were used as nucleating agents and orientation templates for poly(L ‐lactide) (PLLA) crystallization. A fine NHSK structure with controlled lateral size and period of kebabs was successfully obtained under various experimental conditions by using DWNT bundles. This could be due to the geometric confinement effect of the surface groove structure of the DWNT bundles, which could facilitate the orientation of PLLA chains along the DWNT axis and the lateral formation of a stable nucleus. Our work suggests an efficient method for the functionalization of CNTs with biocompatible PLLA, which may have some potential applications in biomedical areas. In addition, it is demonstrated that the formation of NHSK structure can effectively improve the physical bonding between PLLA and nanotubes, thus significantly improving the mechanical properties of PLLA/CNT nanocomposite fibers. Copyright © 2012 Society of Chemical Industry     

Formation of polymer/carbon nanotubes nano-hybrid shish-kebab via non-isothermal crystallization

Multi-walled carbon nanotubes (MWNTs) periodically decorated with polyethylene (PE) lamellar crystals had been prepared using the non-isothermal crystallization method. The morphology and structure of polyethylene attached to MWNTs were investigated by means of transmission electron microscopy (TEM). A nano-hybrid shish-kebab (NHSK) structure was observed wherein the average diameter of PE lamellar crystals varies from 30 to 150 nm with average periodicity of 35-80 nm. The TEM images of samples obtained at 125 °C showed that MWNTs were first wrapped by a homogeneous coating of PE with few subglobules, then PE chains epitaxially grew from the subglobule and formed lamellar crystals perpendicular to the carbon nanotube axis. It is suggested that the homogeneous coating plays a key role in the formation of NHSK structures. And the formation process was discussed based on the intermediate state images of samples obtained at 95 °C. While NHSK structures cannot be formed by using polypropylene (PP). This may attribute to the zigzagged conformation of PP chains on the surface of MWNTs, which hinders the formation of homogeneous coating of PP on it.     

Structure and crystallization behavior of Nylon 66/multi-walled carbon nanotube nanocomposites at low carbon nanotube contents

Multi-walled carbon nanotubes (MWNTs) were modified with poly(hexamethylene adipamide) (also known as Nylon 66) via a controlled polymer solution crystallization method. A “nanohybrid shish kebab” (NHSK) structure was found wherein the MWNT resembled the shish while Nylon 66 lamellar crystals formed the kebabs. These Nylon 66-functionalized MWNTs were used as precursors to prepare polymer/MWNT nanocomposites. Excellent dispersion was revealed by optical and electron microscopies. Nitric acid etching of the nanocomposites showed that MWNT formed a robust network in Nylon 66. Non-isothermal DSC results showed multiple melting peaks, which can be attributed to lamellar thickness changes upon heating. The crystallite sizes L₁₀₀ and L₀₁₀ of Nylon 66, determined by WAXD, decreased with increasing MWNT contents. Isothermal DSC results showed that crystallization kinetics increased first and then decreased with increasing MWNT contents in Nylon 66. This study showed that the effect of MWNTs on Nylon 66 crystallization is twofold: MWNTs provide heterogeneous nucleation sites for Nylon 66 crystallization while the tube network structure hinders large crystal growth.     

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.     

Hierarchical structure of injection-molded bars of HDPE/MWCNTs composites with novel nanohybrid shish-kebab

Injection-molded products usually show hierarchical structure from skin to core due to the existence of shear gradient and temperature gradient. Investigating the hierarchical structure is helpful to better understand the structure-property relationship of injection-molded sample, which is important for design and preparation of polymer products with high performance. In this work, the hierarchical structures of injection-molded bars of high-density polyethylene (HDPE)/multi-walled carbon nanotubes (MWCNTs) composite were explored by examining the microstructure and crystal morphology, layer by layer, along the sample thickness, using SEM, DSC and 2D-WAXS. To enhance the shear effect, a so-called dynamic packing injection molding (DPIM) technique was used to prepare the molded bar with high orientation level. Interestingly, SEM revealed that in the skin and core zones, the lamellae of PE anchored randomly on the surface of MWCNTs, while well-defined nanohybrid shish-kebab (NHSK) entities, in which fibrillous carbon nanotubes (CNTs) act as shish while HDPE lamellae act as kebab, exist in the oriented zone. The changed NHSK crystal structure along the thickness direction of molded bar is considered as due to the shear gradient and thermal gradient in injection molding. And the underlying origin of in situ formation of NHSK under shear effects is discussed based on experimental observations.     

Facilitating the formation of nanohybrid shish kebab structure in helical polymer systems by using carbon nanotube bundles

Periodic patterning of carbon nanotubes (CNTs) with semi-crystalline polymers, especially the novel nanohybrid shish kebab (NHSK) superstructure, in which fibrous CNTs act as shish while polymer lamellae as kebab, is of interest both scientifically and technologically. So far the reported NHSK are mostly prepared using polymers with zigzag conformation in crystal and it seems difficult to obtain NHSK using polymer with helical conformation. In this work, we report the formation of NHSK structure by using single-walled carbon nanotube (SWNT) bundles. A promoted formation of NHSK was observed even using polymer with helical conformation, and the formation mechanism of NHSK was attributed to the unique “groove structure” formed by the stacked SWNTs in parallel arrays, which could facilitate the orientation of helical polymer chains along the SWNTs axis and the lateral formation of stable nucleus. The NHSK structure in helical polymer/SWNT bundles system could widen application of this unique superstructure, offering value in both application field and crystallography aspect as well.     

The morphology evolution of polyethylene produced in the presence of a Ziegler-type catalyst anchored on the surface of multi-walled carbon nanotubes

Data are presented on the evolution of the morphology of polyethylene (PE) formed via in situ polymerization with different polymer yield over a Ziegler-type titanium-magnesium catalyst anchored on the CNT surface. Individual polymer microparticles are formed on the CNT surface at the initial polymerization stage (the yield of 2.5–10 g PE/g CNT) with the formation of PE/CNT composites having a shish-kebab structure. As the polymer yield increases above 10 g PE per g CNT, the size of microparticles increases and the CNT surface gets totally covered with the polymer. We have found also a great effect produced by the morphology of initial CNT particle aggregates of individual nanotubes on the morphology of macroparticles in PE/CNT composites and the uniformity of CNTs distribution in PE/CNT composites. In the case of CNT samples with a loose structure of macroparticles (aggregates of entangled nanotubes), it is possible to obtain a homogeneous distribution of nanotubes in the polymer matrix of composites and increase the electrical conductivity of composites by 1–8 orders of magnitude by varying the CNT content in the composites from 0.9 to 2.8 wt%.     

Fabrication of high‐k poly(vinylidene fluoride)/Nylon 6/carbon nanotube nanocomposites through selective localization of carbon nanotubes in blends

The morphology as well as the distribution of conductive fillers in conductive filler/polymer nanocomposites have a decisive effect on the dielectric properties of blend composites. In this study, the relationship between morphology and properties was carefully investigated and the underlying mechanism is discussed based on the microcapacitor model. Multiwalled carbon nanotubes (CNTs) were introduced into an immiscible poly(vinylidene fluoride) (PVDF)/polyamide 6 (Nylon 6) blend and the morphologies of PVDF/Nylon 6 were tailored by changing the weight ratio of PVDF to Nylon 6, varying from sea‐island morphology to co‐continuous morphology. Interestingly, the CNTs are selectively localized in the Nylon 6 phase in both sea‐island and co‐continuous morphological blends, which is due to the finer interaction between Nylon 6 and CNTs. In the sea‐island morphological blend only, a strong increase of the dielectric permittivity can be found when the content of CNTs is increased. It is surprising that no effects of CNTs on the dielectric properties can be found in the co‐continuous morphological blend. The CNT filled Nylon 6 domains in the sea‐island morphological blend act as a microcapacitor with improved charge accumulation and interfacial polarization, resulting in a marked increase in dielectric permittivity. © 2016 Society of Chemical Industry     

Development of hierarchical structured carbon nanotube‐nylon nanofiber mats

A hierarchical nanofiber (NF) structure featuring carbon nanotubes (CNTs) densely attached on the surface of NFs is presented. Nonwoven NF mats made of Nylon 6 (Nylon) were mass produced using the forcespinning^® (FS) technology, followed by depositing functionalized CNTs (f‐CNTs) on the surface of NFs. Strong interfacial adhesion between CNTs and Nylon NFs was developed by the formation of covalent bonds. The morphology, structure, conductivity, and mechanical properties of the developed CNT‐Nylon NFs were analyzed. The hierarchical NFs have a 338% improvement in tensile strength without compromising its strain at break. The shielding effectiveness (SE) of electromagnetic interference (EMI) was recorded to be 30 dB. These promising characteristics endow novel flexible hierarchical NF mats for applications as EMI shielding materials or smart textiles to mention some. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42535.     

Nanocomposites of ultrahigh molar mass polyethylene and modified carbon nanotubes

In this work, the use of a laboratory twin-screw extruder was evaluated to process ultrahigh molar mass polyethylene and composites with carbon nanotubes (CNTs). Commercial polymer samples with lubricant (1%) and different percentages (0.01%, 0.05%, and 0.1%) of pure, oxidized, and chemically surface treated multi-walled carbon nanotubes (MWCNTs) were evaluated. The results showed that polymer melting and crystallization temperatures were not affected by CNTs, although an increase in the degree of crystallinity in all nanocomposites was observed along with a decrease in crystal size. Therefore, CNTs behaved as nucleating agents. All ultrahigh molar mass polyethylene (UHMWPE)/CNT samples showed increased initial degradation temperature, although this was not very great when introducing acetylated and stearic acid modified CNTs. Both oxidized CNTs and stearic acid CNTs did not markedly improve the composites' mechanical properties. Therefore, the nanocomposites containing pure CNTs and most of those with acetylated CNTs resulted in higher reinforcement for UHMWPE. The addition of the lubricant allowed the polymer matrix to be processed in the extruder, whereas the increase in CNT content in UHMWPE improved the stiffness of the material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47459     

Impact of ultrasonication on carbon nanotube demixing and damage in polymer nanocomposites

While ultrasonication is universally employed for dispersion and distribution of carbon nanotubes (CNTs) in a solvent or polymer solution, the current work focuses on the underlying mechanisms of CNT demixing and CNT damage that can occur during processing. Here, multi-walled CNTs were dispersed in a polycaprolactone polymer matrix using an established solution processing technique. Electrical, rheological, and mechanical characterization results suggest that once nanocomposite property enhancements reach an optimal level, further sonication leads to a decrease in the corresponding properties due to a combination of CNT damage and demixing mechanisms. Evidence of CNT damage from transmission electron microscopy, poor CNT distribution from optical image analysis and shear-induced crystallization results, and reagglomeration observed from ultraviolet–visible results, taken together, suggest that mechanisms of demixing and damage of the CNTs coexist for excessive sonication times.     

Decoration of multi-walled carbon nanotubes by polymer wrapping and its application in MWCNT/polyethylene composites

ABSTRACT: We dispersed the non-covalent functionalization of multi-walled carbon nanotubes (CNTs) with a polymer dispersant and obtained a powder of polymer-wrapped CNTs. The UV-vis absorption spectrum was used to investigate the optimal weight ratio of the CNTs and polymer dispersant. The powder of polymer-wrapped CNTs had improved the drawbacks of CNTs of being lightweight and difficult to process, and it can re-disperse in a solvent. Then, we blended the polymer-wrapped CNTs and polyethylene (PE) by melt-mixing and produced a conductive masterbatch and CNT/PE composites. The polymer-wrapped CNTs showed lower surface resistivity in composites than the raw CNTs. The scanning electron microscopy images also showed that the polymer-wrapped CNTs can disperse well in composites than the raw CNTs.     

CVD growth of secondary carbon nanotubes and its effect on field electron emission

Secondary carbon nanotubes (CNTs) were grown on primary ones by simply changing the methane concentration. No additional catalyst was used throughout the whole deposition process. The CNT growth was carried out using hot filament chemical vapor deposition in a gas mixture of methane and hydrogen. The structure and surface morphology of the deposited CNTs were studied and the field emission properties of the CNTs were tested. It was found that synthesizing primary CNTs at extremely low methane concentration is the key for the secondary growth without additional catalyst. The CNT samples grown with secondary nanotubes exhibited improved field emission properties.     

Lignin-based carbon fibers: Carbon nanotube decoration and superior thermal stability

Lignin-based carbon fibers (CFs) decorated with carbon nanotubes (CNTs) were synthesized and their structure, thermal stability and wettability were systematically studied. The carbon fiber precursors were produced by electrospinning lignin/polyacrylonitrile solutions. CFs were obtained by pyrolyzing the precursors and CNTs were subsequently grown on the CFs to eventually achieve a CF–CNT hybrid structure. The processes of pyrolysis and CNT growth were conducted in a tube furnace using different conditions and the properties of the resultant products were studied and compared. The CF–CNT hybrid structure produced at 850 °C using a palladium catalyst showed the highest thermal stability, i.e., 98.3% residual weight at 950 °C. A mechanism for such superior thermal stability was postulated based on the results from X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, and electron energy loss spectroscopy analyses. The dense CNT decoration was found to increase the hydrophobicity of the CFs.     

Effect of noncovalent chemical modification on the electrical conductivity and tensile properties of poly(methyl methacrylate)/carbon nanotube composites

Noncovalent chemical modification by initiated chemical vapor deposition technique is applied to carbon nanotubes (CNTs) to reduce average agglomerate size of the nanoparticles in the polymer matrix and to improve surface interaction between the composite constituents. CNT surfaces are coated conformally with thin poly(glycidyl methacrylate) (PGMA) polymer film and coated nanoparticles are incorporated in poly(methyl methacrylate) (PMMA) polymer matrix using solvent casting technique. Conformal PGMA coatings around individual nanotubes were identified by scanning electron microscopy analysis. Transmission electron microscopy and optical microscopy analyses show homogeneous composite morphology for composites prepared by using PGMA coated nanotubes. Fourier Transform Infrared and X‐ray photoelectron spectroscopy analyses show the successful deposition of polymer with high retention of epoxide functionality. PGMA coating of CNTs exhibits improvement in electrical conductivity and tensile properties of PGMA‐CNT/PMMA systems when compared with uncoated nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Single-step route to hierarchical flower-like carbon nanotube clusters decorated with ultrananocrystalline diamond

Two distinct forms of carbon, ultra nanocrystalline diamond (UNCD) and carbon nanotubes (CNTs), were synthesized in a single-step process via hot filament chemical vapor deposition for the first time. The synthesized structure displays unique hierarchical flower-like clusters of vertically aligned carbon nanotubes with diameters ranging from 30 to 50 nm conformally coated with UNCD having a grain size in the range of 3–5 nm. The seeding employed a mixture of diamond and nickel nano powders dispersed in a polymer melt, which promoted the self-assembly of sp² and sp³ carbon into hierarchical structures. The UNCD decorated tubes show good field emission properties with low turn-on field, large field enhancement factor, and an excellent current stability over a period of over 400 h. The ability to synthesize flower like structures of CNTs decorated with UNCD by a single-step process opens up new possibilities for the fabrication of robust nanoelectronic devices.     

碳纳米管在炭纤维表面的可控自组装

采用催化化学气相沉积法将碳纳米管(CNTs)原位生长于炭纤维(CF)表面并自组装成不同形貌的CNTs/CF杂化结构。使用扫描电子显微镜、拉曼光谱仪对制备的纳米/微米杂化结构进行微观形貌分析和结构表征。结果显示,随着温度的升高,碳纳米管在炭纤维表面由均匀分布状态转变为取向生长状态,并且长度及石墨化程度均不断增加。结合碳纳米管结构参数的变化,使用纳米悬臂梁模型解释了这一杂化结构的形成机理。模型分析表明,杂化结构的形貌转变是由不同温度下在炭纤维表面生长的碳纳米管的结构参数不同所造成的,因此可以通过调整相关结构参数控制碳纳米管在炭纤维表面的自组装过程。     

Different filler effect of carbon nanotube and graphene nanoplatelet in the poly(arylene ether nitrile) matrix

The different filler effects of identical nitrile‐functionalized carbon nanotubes (CNTs) and graphene nanoplatelets (GNs) in a poly(arylene ether nitrile) (PEEN) matrix were investigated. PEEN/CNT and PEEN/GN composites were prepared by a facile solution‐casting method and systematically investigated for their differences in morphological, thermal and rheological properties. In the PEEN matrix GNs contact one another in a plane‐to‐plane manner, while CNTs are separated. Compared with PEEN/CNT composites, PEEN/GN composites below 2 wt% filler content exhibited higher thermal stability. Rheological properties of the resulting composites indicated that PEEN/GN composites were more sensitive to strain and exhibited higher η*, G′ and G″ than PEEN/CNT composites. The rheological percolation for CNTs is over 2 wt%, higher than that for GNs (around 1 wt%). All these differences originate from the different dimensions and structures of CNTs and GNs: GNs with a flake‐like structure and larger surface area can have stronger physical and interfacial interactions with the polymer matrix. This work gives a comparative view of the different filler effects that functionalized CNTs and GNs can have in the polymer host. With identical processing technology, GNs can show a stronger filler effect than CNTs. © 2012 Society of Chemical Industry