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. 相似文献
Carbon nanotubes (CNTs) have attracted tremendous attention in recent years because of their superb optical, electronic and mechanical properties. In this article, we aim to discuss CNT-induced polymer crystallization with the focus on the newly discovered nanohybrid shish-kebab (NHSK) structure, wherein the CNT serves as the shish and polymer crystals are the kebabs. Polyethylene (PE) and Nylon 6,6 were successfully decorated on single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs), and vapor grown carbon nanofibers (CNFs). The formation mechanism was attributed to “size-dependent soft epitaxy”. Polymer CNT nanocomposites (PCNs) containing PE, Nylon 6,6 were prepared using a solution blending technique. Both pristine CNTs and NHSKs were used as the precursors for the PCN preparation. The impact of CNTs on the polymer crystallization behavior will be discussed. Furthermore, four different polymers were decorated on CNTs using the physical vapor deposition method, forming a two-dimensional NHSK structure. These NHSKs represent a new type of nanoscale architecture. A variety of possible applications will be discussed. 相似文献
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. 相似文献
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. 相似文献
We report on the investigation of the temperature effect on the selective dispersion of single-walled carbon nanotubes (SWNTs) by Poly(3-dodecylthiophene-2,5-diyl) wrapping. The interaction mechanism between polymer chains and SWNTs is studied by controlling the polymer aggregation via variation of the processing temperature. Optical absorption and photoluminescence measurements including time resolved photoluminescence spectroscopy are employed to study the degree of interaction between the polymer in different aggregation states and the carbon nanotubes. At low processing temperatures, results are consistent with the planarization of the polymer chains and with SWNTs working as seeds for polymer aggregation. The formation of small clusters due to the inter-digitation of alkyl tails between neighboring polymer-wrapped SWNTs allows the formation of the SWNT bundles, as experimentally evidenced and investigated by molecular dynamics simulations. The interaction between the tubes within the bundles, which is reflected in the variation of the photoluminescence dynamics of the polymer, can be suppressed by warming up the sample. 相似文献
Single wall carbon nanotubes (SWNTs) incorporated into ceramic matrices are known to impart enhanced mechanical, thermal and electrical properties to the composites formed. Current procedures for their synthesis face challenges, such as, the non-uniform dispersion of the SWNTs and their damage during high temperature processing in a reactive environment. These have led to poor interfacial matrix to SWNT adhesion and the ineffective utilization of the unique properties of the nanotubes. Here we report a rapid, low temperature microwave-induced reaction to create a novel nanoscale silicon carbide (SiC)-SWNT composite. The reaction, which was completed in 10 min, involves the decomposition of chloro-trimethylsilane and the simultaneous nucleation of nanoscale SiC spheres on the SWNT bundles. The bulk composite is a branched tree-like structure comprised of three-dimensionally arrayed SiC-SWNTs. The uniqueness of this approach lies in the formation of a ceramic directly on the SWNTs, rather than physical mixing, or the growth of nanotubes in a ceramic matrix. 相似文献
Imparting molecular recognition to carbon nanotubes (CNTs) by conjugating them with bio-molecules has been an area of great interest as the resulting highly functionalized CNT-bioconjugates find their applications in various fields like molecular level electronics, pharmaceuticals, drug delivery, novel materials and many others. In this work we demonstrate the synthesis of functionally engineered single walled carbon nanotubes (SWNTs)-peptide nucleic acid (PNA) conjugates especially for nanoelectronic applications. Here we exploited the exceptional structural and chemical advantages of PNA (an artificial analogue of DNA) to join SWNTs ropes. SWNT-PNA-SWNT conjugates were synthesized using carbodiimide coupling chemistry and characterized by host of techniques like scanning electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy. The results from different techniques confirm the formation of these conjugates. Theoretical analysis of molecular orbitals obtained by quantum mechanical simulations show that the highest occupied molecular orbital is located on the glutamate linker and that this interface state will align closely to the valence band of the extended SWNT facilitating charge transfer. The unique electrical and structural properties of these conjugates make them a potential candidate for application in CNT based nanodevices. 相似文献
On the basis of the all-atom model, cohesive energies per carbon atom between two single-walled carbon nanotubes (SWNTs) of uniform and different diameters were calculated, and structural stability of SWNT bundles with differing diameters was analyzed. It is found that the cohesive energy per carbon atom exhibits a minimum when the diameter of one tube is a half of that of the other. So we predict that the SWNT bundle formed by two species of tubes with the diameters of D and D/2 is a novel stable structure. In particular, an energy of 17.44 meV per carbon atom is needed for the separation of a single tube of 2.713 nm from the stable arrangement, while only 15.88 meV per carbon atom for the separation of a single tube of 2.713 nm from the hexagonal array of SWNTs of uniform size, which suggests that the special arrangement structure is more stable than the hexagonal array. It is expected that the calculated cohesive energies per carbon atom may provide valuable information for separation and physical properties of the SWNT bundles with differing diameters. 相似文献
Summary: Polyhydroxybutyrate (PHB) is an ideal bioplastic, however, this polymer undergoes a severe embrittlement process because of its spherulitic structure, rendering the material brittle. Using a series of in‐situ rheo techniques, we have previously observed only the rapid initial stage of shish formation, we term a partial shish, which existed at high shears in medium‐molecular‐weight PHB, = 360 000. The shish kebab morphology is anticipated to remove or severely lessen this embrittlement process whilst providing new properties and applications. For medium and ultra high‐molecular‐weight (MMWT, = 360 000/UHMWT, = 5 × 106) PHB 99/1 and 99.5/0.5 blends only a partial shish is identified. However, the initial shish formation stage and subsequent stages were observed at 98/2 and 97/3 blend ratios resulting in a complete shish, we term the full shish, and fiber formation was evident. We believe this fiber morphology achieved by high molecular weights is crucial to sustaining the shish kebab structure for an excessive period.
Left: In‐situ rheo‐light scattering micrograph; 97/3 MMWT/UHMWT PHB at 100 s?1 for 1 s shear shish held at 75 s. Right: In situ rheo‐optical micrograph; PHB fiber morphology observed at 50 s?1 for 2 s shear 98/2 MMWT/UHMWT PHB after 1 min. 相似文献
The ultrahigh molecular weight polyethylene (UHMWPE) fibers were obtained directly from the industrial production line. Two-step industrial hot-drawing-to-specific-drawing ratios were carried out at the temperature of 120 and 130 °C, respectively. Small-angle X-ray scattering (SAXS) measurements using synchrotron radiation were applied to study the evolution of kebab structure and the formation of shish structure. The slight increase of long period and the rapid decrease of lateral sizes indicated the destruction of original lamellae which was accomplished by chain slip resulted in the orientation of lamellae to form shish structure. The decrease of average shish length was explained that the formed new shish structure had shorter shish length than the original shish at the early stage with the high concentration of spinning solution. Wide-angle X-ray diffraction (WAXD) measurements were performed to explore the changes of the degree of orientation of the crystals. It was found that the elevated drawing temperature was benefited to the evolution of the orientational order. The DSC result confirmed the evolution of shish–kebab structure through the melting behavior. 相似文献
Summary: In‐situ rheo small‐angle X‐ray scattering (SAXS), rheo‐light scattering, and rheo‐optical methods were employed to investigate the resultant morphology of polyhydroxybutyrate (PHB) under varying shear flow conditions. Immediately after shear flow application, a highly orientated structure emerged and row nucleation was identified at high shears. Only the initial stages of shish growth (we term the partial shish) were confirmed at excessively high shear conditions. However, only the kebabs were identified at medium shears, below this neither the shish nor kebab were observed. We believe this partial shish is a result of insufficient stability resulting from using such a low‐molecular‐weight species. We conclude that from our observations the shish kebab mechanism appears to display similarities to the Janeschitz‐Kriegl model of precursor formation.
Left: In‐situ rheo‐SAXS two‐dimensional pattern; kebab morphology observed at 100 s?1 for 1 s shear after 160 s. Right: In‐situ rheo‐optical micrograph; PHB row‐nucleated morphology observed at 100 s?1 for 1 s shear after 1 min. 相似文献