Oriented Crystalline Structure Research Articles

Preparation of high performance thermal conductive composites from aluminum plastic packaging waste via Solid-state Drawing

Aluminum-plastic multilayer films have been widely used as the top-grade packaging material due to their exceptional barrier properties. However, the recycling of aluminum plastic packaging waste (APPW) poses a great challenge. To address this issue, we proposed a facile method for recycling APPW using solid-state drawing technology to produce high performance thermal conductivity composites for the first time. The ultrafine APPW with good processability was obtained by solid-state shear milling (S3M), with a low electrical conductivity of less than 10−12 S/cm. The subsequent solid-state drawing of both the aluminum sheet and polymer chain resulted in the formation of an oriented crystalline structure, with the Al sheet acting as an effective nucleating agent. This resulted in a significant increase in tensile strength for HDPE/APPW (30 %) composites, from 21.4 MPa to 116.1 MPa at the drawing ratio of 5. In addition, the in-plane thermal conductivity of HDPE/APPW (50 %) composites reached an impressive 2.5 W/mK, with the tensile strength of 78.8 MPa. Our findings demonstrate the potential of utilizing APPW for the production of value-added composites without requiring separation, with possible applications in heat management for emerging electrical systems and electronic devices.

Regulating Crystal Orientation in VO2 for Aqueous Zinc Batteries with Enhanced Pseudocapacitance.

Although aqueous zinc batteries have attracted extensive interest, they are limited by relatively low rate capabilities and poor cyclic stability of cathodes. The crystal orientation of the cathode is one important factor influencing electrochemical properties. However, it has rarely been investigated. Herein, VO2 cathodes with different crystal orientations are developed via tuning the number of hydroxyl groups in polyol, such as using glycerol, erythritol, xylitol, or mannitol. The polyols serve as a reductant as well as a structure-directing agent through a hydrothermal reaction. Xylitol-derived VO2 shows a (110)-orientated crystalline structure and ultrathin nanosheet morphology. Such features greatly enhance the pseudocapacitance to 76.1% at a scan rate of 1.0 mV s-1, which is significantly larger than that (61.6%) of the (001)-oriented VO2 derived from glycerol. The corresponding aqueous zinc batteries exhibit a high energy storage performance with a reversible specific capacity of 317 mAh g-1 at 0.5 A g-1, rate ability of 220 mAh g-1 at 10 A g-1, and capacity retention of 81.0% at 10 A g-1 over 2000 cycles. This work demonstrates a facile method for tailoring VO2 crystal orientations, offers an understanding of the Zn2+ storage mechanism upon different VO2 facets, and provides a novel method to develop cathode materials toward advanced aqueous zinc batteries.

Formation of highly oriented crystalline structure for polyoxymethylene fiber enables superior intrinsic thermal conductivity

Polyoxymethylene (POM) as an engineering plastic with high performances, has been widely applied, while endowed with superior intrinsic thermal conductivity for POM fibers was conducive to broaden their application in thermal management field, which were usually prepared through melt spinning-hot drawing/heat setting process. In this work, the tension annealing process was further incorporated into fiber production to develop highly orientated crystalline structure of fibers. All fibers have a uniform diameter with axial textures on surface, and the tensile strength/modulus increased remarkably by drawing and annealing process. In melting spinning process, the POM chains pre-oriented under stress, resulting in a slight increase of thermal conductivity. In hot drawing/heat setting process, through stress-induced crystallization of POM fiber, the shish-kebab crystalline structure formed at a low draw ratio (DR), while at high DR, a homogeneous and compact oriented microfibrillar crystalline structure formed. As a result, a significant improvement of crystallinity (Xc: 84.42 %) and orientation degree (fc, fa: 0.94) in crystalline/amorphous region of POM chains contributed to the superior axial thermal conductivity, which increased from 0.286 Wm−1K−1 of bulk POM to 2.131 Wm−1K−1. In annealing process, although Xc increased further to 93.37 % under high temperature, forming a nearly perfect crystal, while the f of annealed fiber remained under tension force but without further increase, the axial thermal conductivity showed no obvious improvement, revealing that orientation of POM chains had a more significant promotion on improving thermal conductivity of POM fibers than crystallization.

Manipulation of perpendicular magnetic anisotropy and spin–orbit torque switching behavior in ferrimagnetic D022-Mn3Ga based multilayers

Perpendicularly magnetized ferrimagnets have shown potential application in nonvolatile, high-density, and ultrafast spintronic devices. Achieving this requires tuning the material performance of ultrathin ferrimagnetic films. Here, we present an experimental demonstration of tunable perpendicular magnetic anisotropy (PMA) and spin–orbit torque (SOT) switching behavior in a ferrimagnetic Heusler alloy D022-Mn3Ga based multilayers by introducing lattice-matching underlayers. It is found that the highly (001) orientated crystalline structure is well maintained, whereas coercivity, anisotropy field, and PMA constant rely heavily on the specific underlayer. Owing to the strong out-of-plane exchange coupling, the PMA constant of Co2MnSi/D022-Mn3Ga is significantly enhanced by four times and reaches 12.1 Merg/cm3. Moreover, the SOT measurements suggest that Fe/D022-Mn3Ga and Co2MnSi/D022-Mn3Ga exhibit analog and abrupt switching dynamics, respectively. This contrasting SOT switching behavior is attributed to different magnetization switching mechanisms, verified by the direct imaging of the nanoscale magnetic domain. These results provide a deep insight into the manipulation of not only fundamental magnetic properties but also SOT switching of ferrimagnetic Heusler alloys.

In Situ Formation of Soft–Rigid Hybrid Fibers Decorated by Sparse Lamellae of PLLA: Achieving Ductile and Heat-Resistant Materials with High Strength

Constructing an oriented crystalline structure with high crystallinity in poly(l-lactide) (PLLA) is one efficient way to improve its mechanical strength, but flexibility is sacrificed because orderly arrangement restricts molecular mobility seriously. In this work, a unique hierarchical structure of soft–rigid hybrid fibers decorated by sparse lamellae of PLLA is in situ constructed successfully to improve mechanical strength and flexibility simultaneously. Through interfacial stereocomplexation between the PLLA matrix and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)–poly(d-lactide) (PHBV-PDLA) copolymers, followed by a strong flow field during the multistage stretching extrusion (MSE), soft–rigid hybrid fibers of PHBV/interfacial stereocomplex crystallites (i-SCs) are formed to not only act as a reinforcement filler but also favor energy-dissipating deformation mechanisms. Moreover, under the coupling effect of hybrid fibers and intense flow field, the sparse PLLA lamella with a stiff shish is obtained. Consequently, nanofibrillar PLLA/PHBV-PDLA composites with a highly oriented structure exhibit high strength (94.1 MPa), considerable ductility (65.7%), and excellent heat resistance (E′140 °C > 310 MPa), compared to sea–island structured PLLA/PHBV-PDLA composites with an isotropic structure (59.3 MPa, 11.7%, and E′140 °C > 60 MPa). Furthermore, nanofibrillar PLLA/PHBV-PDLA composites can maintain ductility (57.7%) and strength (98.3 MPa) for 886 days at ambient temperature. The strengthening and toughening mechanisms based on the unique structure are proposed by investigating the microstructural changes before and after a tensile test. This work provides significant guidance for strong, ductile, and heat-resistant PLLA-based materials for durable applications.

Exploration of disentangled UHMWPE tape as a soft body armour material

Disentangled ultrahigh molecular weight polyethylene (UHMWPE) is a very promising material with extremely high tenacity and modulus. In this work, the effect of drawing on the morphological, physical, and mechanical properties of disentangled UHMWPE tapes was studied. The tapes were characterised by using the density gradient column method , wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), polarised optical microscopy and scanning electron microscopy (SEM). The density and crystallinity of tape improved after each stage of drawing. The unoriented crystalline structure of the as-prepared UHMWPE tape gradually transformed into an oriented crystalline structure on drawing as confirmed by WAXD patterns. As the draw ratio increased, concomitant increase in birefringence, and tensile properties were also noticed. The tape obtained after the final stage of drawing had tensile properties similar to that of gel spun UHMWPE fibres. Hence, this tape was used to make prototype of soft armour panel (SAP) that stopped all the bullets fired when subjected to ballistic test and yielded very low back face signature (BFS) justifying the potential of disentangled UHMWPE tape as a ballistic material.

Super-strong polyphenylene oxide/polyphenylene sulfide blend foam fabricated by constructing highly oriented crystalline structure

Developing high-performance polymer foams is essential for aerospace applications in harsh conditions. Super-strong polyphenylene oxide/polyphenylene sulfide (PPO/PPS) blend foams were fabricated via establishing a combined solid-phase drawing/sc-CO2 batch foaming method to construct an oriented crystalline structure. The incorporation of poly(styrene-co-glycidyl methacrylate) (SG) improved interfacial compatibility between PPO/PPS phase, and the stretchability of the blend was enhanced. Under appropriate draw ratio (DR) and PPS content, a relatively high dissolved CO2 amount resulted in increased cell size, cell density and expansion ratio, while the cell structure was oriented along drawing direction, and fibrillar structures formed and entangled on cell walls. Increasing DR and forming more PPS crystals facilitated the retention of orientation structure, and for oriented foam with 200% DR, the strength and modulus increased by 86% and 140%, respectively compared with isotropic foam. The dense cell structure and oriented fibrillar structure contributed to significantly improved mechanical strength for PPO/SG/PPS foams.

Formation and reinforcing effect of epitaxial oriented crystallization of polyethylene induced by self‐assembly nucleating agent under stress

AbstractA rare earth nucleating agent (RENA) was introduced to fabricate polyethylene (PE) pipe resin, which self‐assembled into various structures in PE melt during processing and further induced PE molecules to epitaxially crystallize on its surface to form, among others, a hybrid shish‐kebab crystalline structure due to good crystallographic matching between RENA and PE. Under stress, the shish structure formed by needle‐like RENA assembly arranged preferentially along the drawing direction, which was beneficial for an orderly arrangement of PE chains epitaxially crystallizing on its surface in the process of stress‐induced recrystallization and thus promoted the formation of a dense oriented crystalline structure with a large number of shish structures, resulting in higher degree of crystallinity and orientation, and lower long period and lateral size of lamellae than those of PE sample. By orientation, compared with PE sample at the same draw ratio, PE‐RENA samples showed much higher tensile strength and modulus. Especially, the oriented PE‐RENA pipes showed an approximately 96% and 100% increase in tensile strength along the hoop direction and internal pressure resistance, respectively, compared with unoriented pipe sample. This work provides a facile method for fabricating highly enhanced PE pipes with wide application prospects. © 2021 Society of Industrial Chemistry.

Synthesis, Characterisation and Antibacterial Properties of Silicone-Silver Thin Film for the Potential of Medical Device Applications.

Silver (Ag) particles have sparked considerable interest in industry and academia, particularly for health and medical applications. Here, we present the “green” and simple synthesis of an Ag particle-based silicone (Si) thin film for medical device applications. Drop-casting and peel-off techniques were used to create an Si thin film containing 10–50% (v/v) of Ag particles. Electro impedance spectroscopy (EIS), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and tensile tests were used to demonstrate the electrical conductivity, crystallinity, morphology-elemental, and mechanical properties, respectively. The oriented crystalline structure and excellent electronic migration explained the highest conductivity value (1.40 × 10−5 S cm−1) of the 50% Ag–Si thin film. The findings regarding the evolution of the conductive network were supported by the diameter and distribution of Ag particles in the Si film. However, the larger size of the Ag particles in the Si film resulted in a lower tensile stress of 68.23% and an elongation rate of 68.25% compared to the pristine Si film. The antibacterial activity of the Ag–Si film against methicillin-resistant Staphylococcus aureus (MRSA), Bacillus cereus (B. cereus), Klebsiella pneumoniae (K. pneumoniae), and Pseudomonas aeruginosa (P. aeruginosa) was investigated. These findings support Si–Ag thin films’ ability to avoid infection in any medical device application.

Thermal stability enhancement of oriented polyethylene by formation of epitaxial shish-kebab crystalline structure

Oriented polyethylene (PE) products usually exhibit thermodynamic instability in oriented crystalline structure under high temperature during long term service. In this work, self-assembly rare-earth nucleating agent (RENA) was innovatively introduced to fabricate oriented PE and induced PE molecules to form stable epitaxial oriented crystalline structure. Compared with oriented neat PE, oriented PE-RENA showed much higher dimensional/strength retention during aging, which reached as high as 90.13%/86.46% after aging at 100 °C for 1000 h, exhibiting high dimensional/mechanical stability. At low draw ratio, PE-RENA exhibited hybrid oriented shish-kebab structure, for which oriented RENA assembly acted as shish structure and PE lamellae acted as kebab structure, while, after aging, new stable anisotropic shish-kebab crystalline structure formed and the crystallinity (Xc) changed slightly. At high draw ratio, highly oriented shish-kebab structure formed, most of which was retained after aging and the changes of Xc/orientation degree was insignificant, while the molecular mobility in crystalline phase/intermediate phase was weakened, exhibiting enhanced thermal stability in oriented crystalline structure.

Titanium nitride, TiXN(1−X), coatings deposited by HiPIMS for corrosion resistance and wear protection properties

The effect of nitrogen content on the structural, mechanical and corrosion properties of titanium nitride (TixN1−x) coatings deposited by high power impulse magnetron sputtering (HiPIMS) is investigated. The XRD results showed a (111) oriented crystalline structure at low nitrogen flow rate Qv(N2), and a mixed (111) and (200) at high Qv(N2). The average grain size was derived from XRD results and was found to increase with increasing N2 flow. The hardness results showed a maximum with variation of nitrogen content. All coatings exhibited excellent protection efficiency in acidic media compared to the uncoated steel samples, with protection efficiency reaching up to 98.9%. For reference, direct current magnetron sputtered (dcMS) coatings were deposited and investigated, confirming the superior performance of the HiPIMS coatings.

Synthesis of Nanostructured Metallic Foams By Plasma Electrolysis Deposition

Within the framework of fundamental physics studies at CEA, laser target experiments are conducted to investigate laser-matter interactions. Some of these experiments require metallic foams samples in a milimetric scale with an apparent volumetric mass within few hundreds milligrams per cube centimeters. Metallic foams materials are developed and studied since few years for their unique properties offered by their aerated structure. For example, due to a high specific surface, metallic foams could find applications in batteries, supercapacitors, as well as chemical sensors. However, all the metallic foams obtained by the processes referenced in the literature do not meet the specifications needed for laser experiments. This is why, the CEA has developed a new and innovative technique to synthetize metallic foams by plasma electrolysis deposition [1].This process consists in applying a voltage within the 20-100V range at a cathode immerged in a solution containing metallic ions. Under these specific conditions, a uniform gaseous sheath is created around the cathode which is then isolated from the liquid. Due to the high electrical field applied at the electrode surface, several electrical plasma discharges are formed between the cathode and the gas/liquid interface. When the electrical discharges meet the solution, metallic cations are reduced to form metallic strands about 100 nm in diameter. The formed strands are all interconnected together to form metallic foam with micrometric porosities [2]. A few millimeters wide foam with a volumetric mass up to 100mg/cc is obtained in about 10 seconds which is very fast compared to classical electrochemical deposition techniques. The foams synthetized can be made up of pure metals (Cu, Au, Pt ...) or alloys (AuCu ...) in accordance to the metallic ions diluted in the solution.In order to control the shape and homogeneity of the synthetized foams, a better understanding of the mechanisms involved in the foams’ growth is required. By direct camera observation, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), we can show that the growth behavior and the structure of the foams vary with the applied voltage. We observe three main growth patterns which seem to correspond to the different propagation modes of streamer type electrical discharges reported in the literature on plasma discharges in dielectric liquids [3,4]. The first one obtained at “low” voltage is composed of very thin strands (Ø < 100 nm) growing linearly with few ramifications. The second one is formed by highly branched strands about 100 to 600 nm in diameter. TEM observations of first and second mode strands show that their structure is monocrystalline and field oriented. A third mode obtained at the highest voltages is made up of strands above 1 µm thick with a shape very similar to the aggregates obtained in diffusion limited conditions [5]. Voltammetry studies conducted on the electrolytes show that the reduction of metallic species are indeed diffusion limited. Moreover a lower limit current corresponds to a more predominant germination phenomenon on strands. The mass transportation plays a major role alongside the applied voltage in defining the growth mode of the metallic foams and the microstructure of the strands. The structure of the metallic strands and it’s evolution with the synthesis parameters seems in accordance to the electrodeposition theory [6]. However if our results indicate that the reduction and crystallization of the strands may result from an electrochemical process, the field oriented crystalline structure obtained is unlikely to be possible inside an aqueous electrolyte with the speed of growth observed. We conclude this work by proposing an original mechanism for the growth of the foam involving electrochemistry within a plasma medium.

Highly reinforcing effect of polycarbonate/poly(ethylene terephthalate) blends by formation of orientation microfibrillar structure

AbstractHighly oriented microfibrillar polycarbonate/poly(ethylene terephthalate) (PC/PET) blends were prepared. Before orientation, the molecular chains of the blends were mostly randomly arranged with a low crystallinity, and low mechanical properties were obtained. Under stress, it was difficult for molecular chains of the amorphous PC phase in blends to form an oriented crystalline structure. With increasing draw ratio, the crystallinity and orientation degree of the PET phase increased, forming a dense lamellar structure with reduced crystalline and amorphous layer thickness, while with increasing PET content the crystalline orientation degree of the PET phase increased with larger sized lamellae. Moreover, the cross‐section of the oriented sample showed an obvious ordered microfibrillar bundle structure, which arranged compactly and orderly along the drawing direction. The tensile strength and modulus of the oriented PC/20 wt% PET sample were up to 126.01 and 7170.10 MPa, which were 66.48% and 317.49% respectively higher than those of pure PC. Therefore, the stress‐induced oriented microfibrillar structure of the PET phase exhibited a highly reinforcing effect on the PC phase and the blend. © 2021 Society of Industrial Chemistry.

Stabilization of high-temperature Ag2Se phase at room temperature during the crystallization of an amorphous film

Amorphous films of Ag2Se were prepared by laser ablation. After being heated up to 270 °C, the films form oriented crystalline structure of orthorhombic β-modification upon further cooling at temperatures of 110 – 90 °С. The films undergo reversible β↔α phase transitions during the following temperature cycling, while the oriented crystalline structure stays the same. X-ray analysis showed no impurities reflections, excluding the one with very low intensity attributed to an elemental silver. The silver nanocrystals apparently form due to the selenium evaporation from the film surface during heating. The temperature dependence of the film's conductivity coincides with the one for bulk stoichiometric Ag2Se samples.It was shown that a considerable amount of α-Ag2Se is preserved in the film at room temperature even at low cooling rate. This phase is subjected to a significant mechanical stress caused by a density difference between α and β modifications. This circumstance points to the possibility of stabilization of high-temperature superionic modification of Ag2Se at room temperature in a nanolayered structure, in which some alternating layers create a similar stress on the Ag2Se layers.

Formation of Horizontally and Vertically Oriented MoS2 and MoSe2 Films Using Cracked Small S- and Se-Molecules and Its Applications for Transparent a-Si:H Thin Film Photovoltaic Devices

Molybdenum dichalcogenide films (MoX2, X=S, Se) were fabricated on 6-inch wafers by a breakthrough technique utilizing cracked small X-molecules. Uniformly deposited Mo-metal films were sulfurized or selenized by reactive chalcogen (Xa, a= 1- 2) small molecules, and MoX2 film was approximately 3 times thicker than the Mo metal precursor. The behavior of reaction chamber pressure according to the cracking temperature indicated that one large molecule could crack into 4 – 5 small particles in experimental condition used in this work. The formation of protrusions was also effectively inhibited to obtain MoX2 films of a device quality. First, I will explain how effectively large chalcogen molecules (normally X8) were cracked, and the cracking effect on the film quality. By controlling the cracking temperature separately, we could lower the growth temperature down to 400 oC or lower. The effect of cracking and X-source evaporation temperatures on the film quality will be also presented. The film quality was dependent on the deposition technique of Mo metal films. The films were characterized using x-ray photoelectron spectroscopy (XPS), Raman scattering, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Cross sectional high resolution TEM image, energy-dispersive x-ray spectroscopy, and angle-resolved XPS analysis of 6 nm-thick MoS2 sulfurized at 570 oC showed that the film has well-aligned layer-by-layer crystalline structure and the composition and chemical states were uniform through depth. Normally, layer-by-layer grown MoX2 films on very flat surfaces are studied for device applications as reported in earlier works. But, practical devices require the growth of semiconductor films on rough and/or patterned surfaces. Then, we studied the formation of a few nm-thick and a few tens nm-thick MoX2 films on rough surfaces, and found that the MoX2 films could be successfully grown on a very rough substrate (root mean square roughness = 38 nm) using the method introduced in this work. When MoX2 films were grown by chalcogenizing Mo, the crystalline orientation of MoX2 films depended on the thickness of Mo films. When the Mo film is thinner than 5 nm, we could obtain layer-by-layer structured, i.e., MoX2 films. We had reported the successful application of the horizontally grown MoX2 film to the field effect transistors in the previous work [1]. Contrarily, when the Mo film was 5 nm or thicker, the formed MoX2 films had vertically oriented crystalline structure. It is because the stress due to 3 times volume expansion should be released by changing the crystalline orientation from planar layer-by-layered to vertically oriented structures. In this work, we utilized the vertically oriented MoX2 films as an interlayer between the semiconductor layer and the electrode. By adopting the MoX2 interlayer in amorphous silicon (a-Si:H) thin film photovoltaic devices having the inverted structure, we could obtain greatly improved cell performances. In the substrate type photovoltaic cells, the shunt resistance increased from 10 kΩ (no MoSe2) to 18 kΩ (with MoSe2) and the open circuit voltage increased from 0.717 V to 0.785 V. The a-Si:H photovoltaic cell having 26 % visible light transmittance on a glass substrate showed the conversion efficiency of 7.7 % under blue light irradiation of 7 mW/cm2. In conclusion, the horizontally and vertically oriented MoX2 films of high crystallinity were formed by chalcogenizing Mo metal films using reactive cracked small X-molecules, and the use of MoX2 film as an interlayer greatly improved the performance of a-Si:H thin film photovoltaic devices. The growth method introduced in this work would be one of the most promising methods to obtain uniform and high quality metal dichalcogenide films on a large substrate. The most important advantage of this method is that it can be easily applied to other metal chalcogenide materials. [1] Jung, K. H.; Yun, S. J.; Choi, Y.; Cho, J. H.; Lim, J. W.; Chai, H.-J.; Cho, D.-H.; Chung, Y.-D.; Kim, G. Nanoscale 2018, 10, 15213-15221.

High-tenacity and high-modulus polyimide fibers containing benzimidazole and pyrimidine units

Polyimide fibers (PI) combine high thermal stability, good chemical and UV resistance. However, most commercial PI fibers including P84®, Kermel®, Yilun® and Suplon® do not exhibit sufficiently high mechanical properties. Finding an appropriate method that is commercially available to prepare PI fibers with a high tenacity and modulus is required urgently for making large scale manufacturing attractive. Herein, we describe an approach to preparing high-performance PI fibers by introducing the heterocyclic pyrimidine and benzimidazole units into PI backbones. PI fibers prepared by this way exhibited a higher tenacity and modulus compared to those previously reported PIs and even Kevlar 49® fibers due to the high molecular weight, strong hydrogen bonding interaction and highly oriented crystalline structure. In addition, the detailed structural analysis based on WAXD and SAXS has revealed that the stress-induced crystallization and more compact morphology formed in PI fibers by the post hot-drawing process. Accordingly, as the drawing ratio was set to 3.8, an optimum tenacity and modulus of the PI fiber reached to 2.3N/tex and 71.8N/tex, respectively, indicating that the resultant fibers have a great potential application as the reinforcing fiber in advanced composites.

Preparation and Self‐Repairing of Highly Oriented Structures of Ultrathin Polymer Films

AbstractThin and ultrathin polymer films play an important role in a variety of applications, such as electronics, liquid crystal alignment, adhesion, and so on. It is well established that the properties of semicrystalline polymeric materials depend remarkably on their multiscale structures; for example, an increase of more than a factor of 100 has been reported for the electrical conductivity of doped and aligned conjugated macromolecules compared with their nonoriented counterparts. Consequently, sophisticated methods have been developed for preparing highly oriented polymer ultrathin films. It should be pointed out that the highly oriented crystalline structure of polymers can be maintained only at temperatures below their melting points. Otherwise, structure rearrangement will result in the loss of orientation and therefore the properties. Therefore, self‐repairing of highly oriented polymer structures is of great significance for the long‐term application of polymer thin films in some specific fields. In this review paper, the preparation and self‐repair of the highly oriented structure of polymer thin films is described in the hopes that this will afford useful information for further development of polymeric materials for advanced applications.

Crystallization Behavior and Mechanical Properties of Microinjection Molded High Density Polyethylene Parts

Ultra-thin high density polyethylene (HDPE) parts with two different molecular weights were prepared by microinjection molding (MIM). The dependence of crystalline morphology and orientation, as well as the resulting mechanical properties of the samples, on molecular weight is described. The toughness of the high-molecular-weight (HMW) sample was over 2 times that of the low-molecular-weight (LMW) one, in parallel with a significant increase of tensile strength. Microstructure characterizations, including differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS), were performed to investigate the variations of the microstructure. It is suggested that the increased crystallinity and higher degree of both molecular and lamellar orientation were beneficial to the enhancement of strength of the HMW sample. SAXS results showed that a highly oriented crystalline structure, i.e. shish-kebabs, were formed in parts of both of the two HDPE. Furthermore, a larger number of shish and kebab structure or lamellae was formed in the HMW sample due to the fact that the crystallinity was increased and the lamellar thickness and lateral crystallite size was reduced. Therefore, a stronger physical cross-linking network was formed in the HMW sample because of the increased connection points, which was in favor of the notable improvement of toughness. We suggest this issue is of great significance for achieving materials with high performance by tailoring the microstructure.

Ultrathin and Edge-Enriched Holey Nitride Nanosheets as Bifunctional Electrocatalysts for the Oxygen and Hydrogen Evolution Reactions

Exploring economically efficient electrocatalysts with good electrocatalytic activity is essential for diverse electrochemical energy devices. Series of ultrathin metallic nickel-based holey nitride nanosheets were designed as bifunctional catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). They exhibit improved catalytic properties owing to the inherent advantages of their plentiful active reaction sites resulting from the complete exposure of the atoms in the large lateral surfaces and from the edges of pore areas, together with expanded lattice spacing distance. This obtained three-dimensional conductive integral architecture can not only accelerate the electron transportation by the highly orientated crystalline structure but also facilitate the diffusion of intermediate and gases. In terms of the OER electrocatalytic properties, a quite low overpotential (300 mV) is required for the holey two-dimensional (2D) Ni3Fe nitride nanosheets to deliver a current density o...

Crystalline orientation preference for TiO2 nanotube arrays with efficient photoelectrochemical properties

Novel TiO2 nanotube arrays (TiO2 NTAs) with preferred oriented crystalline structure were firstly achieved by a facile method through anodizing Ti sheets with textured microstructure. Highly oriented crystalline structure of TiO2 NTAs, with its (004) lattice plane of anatase TiO2 paralleling to the top surface of TiO2 NTAs was identified by the results of XRD, which was further confirmed by the regular diffraction spots and lattice fringes with uniform direction in HRTEM images. In comparison with normal randomly oriented TiO2 NTAs, the quasi-single crystal structure of highly oriented TiO2 NTAs can suppress the recombination of photogenerated electron–hole pairs and enhance the transfer of photocarriers, as was proved by the photoelectrochemical measurement conducted on both normal TiO2 and oriented TiO2 NTAs. The results of this study provide a promising avenue to obtain high photoelectrochemical performance TiO2 NTAs-based hybrid nanomaterials.