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The crystallization of entangled polymers from their melt is investigated using computer simulation with a coarse-grained model. Using hybrid Monte Carlo simulations enables us to probe the behavior of long polymer chains. We identify solid-like beads with a centrosymmetry local order parameter and compute the nucleation free-energy barrier at relatively high supercooling with adaptive-bias windowed umbrella sampling. Our results demonstrate that the critical nucleus sizes and the heights of free-energy barriers do not significantly depend on the molecular weight of the polymer; however, the nucleation rate decreases with the increase in molecular weight. Moreover, an analysis of the composition of the critical nucleus suggests that intra-molecular growth of the nucleated cluster does not contribute significantly to crystallization for this system., National Key R&D Program of China (2016YFB0302500); National Natural Science Foundation of China (51633009); Royal Society Newton Mobility Grant (MBAG/240 RG82754)

Load-bearing biological tissues, such as muscles, are highly fatigue-resistant, but how the exquisite hierarchical structures of biological tissues contribute to their excellent fatigue resistance is not well understood. In this work, we study antifatigue properties of soft materials with hierarchical structures using polyampholyte hydrogels (PA gels) as a simple model system. PA gels are tough and self-healing, consisting of reversible ionic bonds at the 1-nm scale, a cross-linked polymer network at the 10-nm scale, and bicontinuous hard/soft phase networks at the 100-nm scale. We find that the polymer network at the 10-nm scale determines the threshold of energy release rate G(0) above which the crack grows, while the bicontinuous phase networks at the 100-nm scale significantly decelerate the crack advance until a transition G(tran) far above G(0). In situ small-angle X-ray scattering analysis reveals that the hard phase network suppresses the crack advance to show decelerated fatigue fracture, and G(tran) corresponds to the rupture of the hard phase network.

As a strategy for regulating entropy, thermal annealing is a commonly adopted approach for controlling dynamic pathways in colloid assembly. By coupling DNA strand-displacement circuits with DNA-functionalized colloid assembly, we developed an enthalpy-mediated strategy for achieving the same goal while working at a constant temperature. Using this tractable approach allows colloidal bonding to be programmed for synchronization with colloid assembly, thereby realizing the optimal programmability of DNA-functionalized colloids. We applied this strategy to conditionally activate colloid assembly and dynamically switch colloid identities by reconfiguring DNA molecular architectures, thereby achieving orderly structural transformations; leveraging the advantage of room-temperature assembly, we used this method to prepare a lattice of temperature-sensitive proteins and gold nanoparticles. This approach bridges two subfields: dynamic DNA nanotechnology and DNA-functionalized colloid programming.

Conventional polymeric adsorbents encapsulate most of their ligand groups (such as amidoxime, AO) in dense structures, leading to problems such as low adsorption capacity for uranium extraction from seawater (UES). The uranium coordination environment of polymeric adsorbents has not been positively identified even after decades of research. Therefore, a new and functional biaxially stretched polyethylene (BSPE) membrane with poly-amidoxime (PAO) nanoparticles, mesoporous architecture, and nano-channels (PAO-BSPE) was fabricated in this study for UES, based on the interfacial self-assembly of axial grafting chains. The underlying mechanism involved in the formation of the PAO-BSPE membrane was elucidated using first-principles computations of the various reactions. The engineered PAO-BSPE membrane exhibited excellent hydrophilicity, good mechanical properties, high specific surface area, and contained mesoporous architecture and nano-channels, which facilitated advantages in terms of kinetics, capacity, and renewability in both laboratory experiments and marine field-testing. After 64 days of adsorption in natural seawater, the PAO-BSPE membrane with a low degree of grafting of 70.5% exhibited a high uranium-adsorption-capacity of 12.67 mg-U/g-ads, which was 1.77 times higher than that toward vanadium. The PAO-BSPE membrane efficiently extracted uranium in the presence of high concentrations of co-existing ions, with the distribution coefficient reaching 4.09 × 106 mL/g in natural seawater. The total amount of uranium recovered by the PAO-BSPE membrane was 15.0 g in terms of yellow cake during a total submersion time of 30 days in the ocean. The adsorbent exhibited a long service life of at least 12 cycles. Furthermore, near-edge and extended X-ray absorption fine structure spectroscopy analyses suggested that the mechanism of uranium adsorption involved the formation of a stable complex via the linkage of uranium with two amidoximes in a cooperative chelating fashion. This study presents a new adsorbent with improved efficiency for UES, which has significant implications for the development of polymer adsorbents with high selectivity.

Stretch-induced crystallization (SIC) and phase transitions of poly(dimethylsiloxane) (PDMS) have been studied with the in situ synchrotron radiation wide-angle X-ray scattering technique (WAXS) du...

The smart flexibility of phase transitions in liquid crystals (LCs) makes them suitable for various applications and is an important research field in contemporary science, engineering, and technology. Unlike most reports focused on bent-core LCs in the thermotropic situation, in our present study, we designed and synthesized a fully rigid bent-core molecule with the sulfonic acid group replacing conventional flexible chains. A rich variety of counterion-induced supramolecular LC phase behaviors have been systematically investigated. It was found that the smectic phase with nanosheets tends to transform to the hexagonal phase with nanofilaments when the protons of the sulfonic acid group are partially replaced by alkali metal ions. The experimental results show that the nanoaggregate and phase transition are controlled by the displacing ratio of alkali metal ions rather than the molecular concentration. Another interesting feature is that the achiral bent-core molecules self-assemble into columns by helical stacking and present macroscopic chirality, indicating that spontaneous chiral symmetry breaking occurs in the columnar phase. The fully rigid bent-core molecules reveal surprisingly hierarchical molecular self-assemblies with the smectic-to-hexagonal phase transition, which was not previously observed in supramolecular complexes. The findings will provide new possibilities for applications in LC-based photonic devices, biosystem switches, and supramolecular actuators.

Lamellar stack in semicrystalline polymers composed of alternatively arranged lamellar crystal and amorphous layers is one of the typical hard-soft laminated nano-composites. Considering the Poisson contraction effects during uniaxial tensile deformation along the normal direction of layers, microbuckling instability of lamellar stacks is first proposed as a new deformation mechanism to trigger the nonlinear mechanical behaviors in semicrystalline polymers. Based on the non-equilibrium process of crystallization and experimental observations, a three-phase structure with lamellar stack (crystal and interlamellar amorphous) and the amorphous matrix is proposed as a deformation unit in semicrystalline polymers. Based on the three-phase model and the proposition of buckling with shear mode, we deduce the theoretical critical strain for the sinusoidal microbuckling through linear stability analysis method. Taking hard-elastic isotactic polypropylene as an example, the theoretically calculated critical strain is in a good agreement with the experimental critical strain at temperatures below α relaxation temperature Tα. These results suggest that elastic microbuckling is indeed a possible mechanism to trigger the nonlinear instability, which is different from current plastic deformation models with crystal destruction around yield in semicrystalline polymers.

A wireless massive multiple-input multiple-output (MIMO) system entails a large number of base station antennas serving a much smaller number of users, with large gains in spectral efficiency and energy efficiency compared with the conventional MIMO technology. Until recently, it was believed that as the number of base station antennas tends to infinity, the performance of such systems is limited by directed inter-cellular interference caused by unavoidable re-use of training sequences (pilot contamination) by users in different cells. We devise a new concept of large-scale fading precoding (LSFP) that leads to the effective elimination of inter-cell interference. The main idea of LSFP is that base stations linearly combine messages aimed at users from different cells that re-use the same training sequence. Crucially, the combining coefficients depend only on the large-scale fading coefficients between the users and the base stations. These coefficients change slowly and their number does not depend on the number of base station antennas. Thus, the traffic between base stations stays constant even if the number of antennas tends to infinity. Furthermore, we derive a capacity lower bound for massive MIMO systems with LSFP and a finite number of base station antennas. In this regime, mitigation of all types of interference, not only the pilot contamination, is required. We consider optimal and suboptimal LSFP precodings that take into account all sources of interference. Our simulations results show that LSFP provides significant gain even for the case of moderate number of base station antennas.

Synchrotron radiation (SR) provides highly brilliant light with tunable wavelength from hard X-ray to far infrared, on which scattering, spectroscopy and imaging techniques with high time and spatial resolutions have been developed for in situ study on biological system and materials like polymer. With examples on flow-induced crystallization of polymer, deformation of nanoparticle filler network in rubber composite and necking propagation in tensile stretch, current work attempts to demonstrate the advantages of in situ synchrotron radiation X-ray scattering, X-ray nano-CT and infrared imaging in the study of deformation-induced multi-scale structural evolutions of polymers. With time resolution up to sub-ms, synchrotron radiation is expected to play a great role in understanding non-equilibrium polymer physics under processing and service conditions, while high-throughput characterization platform based on synchrotron radiation opens the possibility to establish polymer Materials Genome database in processing parameter space within reasonable time, which can serve as the roadmap for industrial polymer processing and accelerate material innovation.

Lamellar stacks, arranged alternatively with hard crystal and soft amorphous nano-layers, are the basic building units to determine the intrinsic mechanical properties of semi-crystalline polymeric materials. The mechanical instability of hard-elastic isotactic polypropylene (iPP) films with highly parallel lamellar stacks is studied with in-situ synchrotron radiation small- and wide-angle X-ray scattering (SAXS/WAXS) techniques during cyclic tensile deformation. Unexpectedly, the micro-strain, deduced from the relative variation of lamellar periodicity, shows an accelerated increase at the onset of instability and reaches values larger than the corresponding macro-strain after yield, during which no irreversible plastic destruction of crystal is observed. Combining the unpredictable increase of long period and other structural information obtained with in-situ SAXS/WAXS measurements, we propose that stress-induced microphase separation of interlamellar amorphous phase is responsible for the yield behavior and the hyperelasticity of hard-elastic iPP films, which stems from the heterogeneous distribution of tie chain/trapped entanglement in interlamellar amorphous nano-layers. This reversible stress-induced non-equilibrium phase transition of interlamellar amorphous phase is different from current plastic deformation models with crystal destruction in semi-crystalline polymers but in line with the nearly 100% elastic recovery ratio of hard-elastic films.

Combining a homemade film blowing machine and an in situ synchrotron radiation source with small- and wide-angle X-ray scattering (SAXS and WAXS) capability, an investigation of film blowing of pol...

The stretch-induced coil–helix transition (CHT) of isotactic polypropylene (iPP) was studied with full-atom molecular dynamics (MD) simulations during the uniaxial stretch process. The results show that imposing stretch induces CHT, which increases both the content and the average length of helices. As strain exceeding a certain value, long helices initially not presented in melt start to emerge, which mainly follow a kinetic pathway of merging adjacent short helices, while overstretch at large strain leads to the helix-extended coil transition. Based on statistics on the distribution of helical length and theoretical calculation, stretch is found to reduce free energy gap for CHT. At small strain, the single-chain model is sufficient to account stretch-induced CHT for the formation of short helices, but the gap reduction is mainly contributed by intrachain energy rather than entropy, which is different from current theories for stretch-induced CHT. While the formation of long helices at large strain requ...

The structural evolution (not only intra-fibrillar but also inter-fibrillar structures) during extension of poly (vinyl alcohol) (PVA) in water at different temperatures are investigated by in-situ small- and wide-angle X-ray scattering (SAXS and WAXS). The stress-strain curves can be defined into four zones with the onset and the end of stress plateau, and the strain hardening point as the zone boundaries. WAXS results show that stretch induces melting of PVA crystal from zones I to III, while SAXS measurements reveal stretch-induced transformation from initial lamella to nanofibrils starts at the onset of zone II, which proceeds via a melting-reconstruction process instead of direct transformation. In zone III, the nanofibrils increase in content and pack periodically with an average inter-fibrillar spacing of about 14–18 nm. Increasing temperature leads to larger inter-fibrillar spacing and more perfect packing of nanofibrils, which may benefit the production of polarizer with homogeneously structural and optical properties.

Structure evolution of slightly oriented high density polyethylene (HDPE)-plasticizer film is recorded with small- and wide- angle X-ray scattering (SAXS/WAXS) during stretching. The HDPE has number average molecular weight (Mn) of 300 kg/mol and polydispersity index (Mw/Mn) of 20, respectively. The plasticizer is mixture of aliphatic hydrocarbon with chain length of 11–13 carbon atoms. Experiments are carried out at industrially relevant conditions, with film thickness of 650 μm, plasticizer content of 56%, strain rate of 0.5 s−1 and stretch temperature from 80 °C to 100 °C, respectively. An interesting evolution of SAXS patterns from anisotropic ring, four-point, six-point, and two-lobule is observed. From WAXS data, a monotonous increasing after the first decline of crystallinity is obtained, by which melting-recrystallization is validated to occur during stretching. With peak shift of WAXS pattern at different azimuthal angle (Φ), triaxial local stresses exerted on lamellae oriented along different directions are acquired. As consequence, stress exerted along and that perpendicular to chain direction are revealed to induce melting of lamellae at azimuthal angle from 0° to 60° and that from 60° to 90°, respectively. Due to the heterogeneous stress distribution of the system, the appearance of four-point SAXS pattern stems from the sequential melting of lamellae at different azimuthal angles. Through thermodynamic analysis, the physical essence of stress induced melting of lamellae is validated to be elastic energy driven crystal to amorphous phase transition.

The effects of temperature on the nonlinear mechanical behaviors of hard-elastic isotactic polypropylene films are systematically studied with in-situ ultrafast synchrotron radiation small- and wide-angle X-ray scattering techniques (SAXS/WAXS) during uniaxial tensile deformation at temperatures from 30 to 160 °C. Based on the mechanical behaviors and structural evolutions in strain–temperature two-dimensional space, three temperature regions (I, II, and III) are clearly defined with the α relaxation temperature (Tα ≈ 80 °C) and the onset of melting temperature (Tonset ≈ 135 °C) as boundaries, where different mechanisms dominate the nonlinear deformations after yield. In region I, microstrain in lamellar stacks em obtains an accelerated increase after yield and reaches a value significantly larger than corresponding macrostrain e, during which neither slipping, melting, nor cavitation occurs. We propose stress-induced microphase separation of interlamellar amorphous to be responsible to the hyperelastic b...

Flow-induced crystallization (FIC) is a typical nonequilibrium phase transition and a core industry subject for the largest group of commercially useful polymeric materials: semicrystalline polymers. A fundamental understanding of FIC can benefit the research of nonequilibrium ordering in matter systems and help to tailor the ultimate properties of polymeric materials. Concerning the crystallization process, flow can accelerate the kinetics by orders of magnitude and induce the formation of oriented crystallites like shish-kebab, which are associated with the major influences of flow on nucleation, that is, raised nucleation density and oriented nuclei. The topic of FIC has been studied for more than half a century. Recently, there have been many developments in experimental approaches, such as synchrotron radiation X-ray scattering, ultrafast X-ray detectors with a time resolution down to the order of milliseconds, and novel laboratory devices to mimic the severe flow field close to real processing conditions. By a combination of these advanced methods, the evolution process of FIC can be revealed more precisely (with higher time resolution and on more length scales) and quantitatively. The new findings are challenging the classical interpretations and theories that were mostly derived from quiescent or mild-flow conditions, and they are triggering the reconsideration of FIC foundations. This review mainly summarizes experimental results, advances in physical understanding, and discussions on the multiscale and multistep nature of oriented nuclei induced by strong flow. The multiscale structures include segmental conformation, packing of conformational ordering, deformation on the whole-chain scale, and macroscopic aggregation of crystallites. The multistep process involves conformation transition, isotropic-nematic transition, density fluctuation (or phase separation), formation of precursors, and shish-kebab crystallites, which are possible ordering processes during nucleation. Furthermore, some theoretical progress and modeling efforts are also included.

A well-known Phan-Thien and Tanner differential viscoelastic constitutive equation has been employed to analyze the nonlinear stability and dynamics of nonisothermal film casting. A finite element method combined with stabilization techniques including discrete elastic viscous stress splitting and the streamline upwind Petrov–Galerkin method was first performed for the numerical calculation of transient film casting. Therefore, the stability analysis of film casting was carried out based on a wider parameter space of processing and the rheological properties of the polymer melt, during which the critical draw ratio for the occurrence of draw resonance (Drc) was taken as an indicator for flow stability. Unlike the results predicted by the upper-convected Maxwell model, the stabilizing region upon an upper critical draw ratio is nonexistent, while more than one peak of Drc was observed with varying aspect ratios, which was dominated by two deformation types named planar and transitional deformations, respec...

In the present study, microstructure and mechanical properties of casting Al-3Li-2Mg-1Zn-0.1Zr alloys modified by Sc additions have been investigated. As-aged Al-3Li-2Mg-1Zn-0.2Sc-0.1Zr alloy possesses a desirable comprehensive mechanical performance. The YS, UTS and El reach 253 MPa, 406 MPa and 7.4% respectively. With the addition of Sc, a more than 50% reduction in the grain size was achieved by the promoted heterogeneous nucleation on primary Al3(Sc, Zr) phases and the grain growth resistance was enhanced by the Zener pinning. After the heat treatment, core-shell composite particles precipitated from the matrix. The shell consists entirely of Al3Li phases. In contrast, both Al3(Sc, Zr) and Al3Sc cores can be observed in the Sc-containing alloys. Increasing the Sc content from 0.1 wt% to 0.2 wt%, the mean radius of cores increases, while the mean width of shells and the number density of particles seem not to be affected. With the passage of ageing time, the coarsening of composite particles occurred, though the dimension of the core remained almost constant. The kinetics follows the KV model and the exponent (n−1) is about 0.11, which is lower than the expected value (0.33) probably due to the unreached quasi-steady-state at the present low temperature.

Aiming to reveal the effects of mechanical energy and thermal effect on micropore nucleation and growth in oriented high density polyethylene (HDPE) film, stress relaxation after cold stretching was imposed at low and elevated temperature with strain holding constant, respectively, and corresponding structure evolution was tracked by in situ and ex situ small angle X-ray scattering (SAXS). It was found that stress-induced density fluctuation during cold stretching could be completely recovered as soon as the stress was unloaded, which was called as micropore embryo. Mechanical energy release at low temperature can promote micropore nucleation after an induction period. However, the growth of micropore nuclei is inhomogeneous, developing as non-uniform micropores with poor interconnectivity during hot stretching. While during temperature elevation, micropore embryos can be converted into evenly distributed micropores together with formation of fibrils, which can supply growth sites for through pores during hot stretching. Consequently, microporous membranes with narrow micropore size distribution and good permeability could be obtained after the subsequent hot stretching.

The tritium analysis in tritium/deuterium-containing zirconium thin films was performed using elastic backscattering spectrometry (EBS) and β-ray induced X-ray spectrometry (BIXS). The EBS energy spectra were simulated with the SIMNRA program to obtain the tritium depth profiles and the total tritium contents in the samples. Two stopping powers used in the SIMNRA program were compared and it was shown that the SRIM stopping power in the simulations was better than the Ziegler/Biersack stopping power. In the BIXS that incorporated Monte Carlo simulation data, the β-ray stopping layers between the X-ray detector and the sample were Al thin film (BIXS-Al) and Ar gas (BIXS-Ar), respectively. The pile-up effects for BIXS X-ray spectra were corrected using Monte Carlo method for the first time. The tritium depth profiles and the total tritium contents in zirconium thin films obtained by the BIXS-Ar, BIXS-Al, EBS and the pressure, volume and temperature (PVT) method were compared. The possible reasons for the difference between the BIXS-Ar and BIXS-Al were discussed and the generality of Al thin film as the β-ray stopping layer was tested and a standard procedure of BIXS method for analyzing tritium-containing solid materials was proposed, in which the BIXS-Al method was recommended.

By comparing the brittle-ductile transition (BDT) behavior between uniaxial width-Free Melt pre-Stretched (FMS) and width-Constrained Melt pre-Stretched (CMS) poly(methyl methacrylate) (PMMA), the effect of molecular alignment on the mechanical response of glassy polymers has been investigated. Unexpectedly, during further mechanical characterization, CMS samples exhibit higher ductility than FMS samples along both the machine (stretching) direction (MD) and the transverse direction (TD). Combining the results from molecular orientation and stress relaxation, it is proposed that chain stretching and aligned chain density is responsible for the ductile deformation along the MD and TD, respectively. Along the MD, CMS samples exhibit more significant chain stretching than FMS samples due to width constraint, leading to a lower chain activation energy barrier in CMS samples. Upon further deformation, chain activation is then accelerated and shear yielding can be achieved at lower temperature. Along the TD, the orientation function remains constant for CMS samples but negatively increases for FMS samples, and the lower aligned chain density in FMS samples increases the activation energy barrier for plastic deformation. As a result, crazing prevails during further deformation for FMS samples and causes weaker ductility. The mode of BDT in glassy polymers is considered from multiple scales.

Oblique stretching is a special approach for the fabrication of polymer film whose product is mainly used in the optical display field, such as compensation films, retardation films, et al. Nonetheless, the previous research reports on oblique stretching processing are still lacking, and the related numerical research is almost blank. This contribution uses the FEM (finite element method) to simulate the oblique stretching process of viscoelastic polymer film for the first time. The differential viscoelastic PTT (Phan-Thien and Tanner) model, one of the most realistic constitutive models is chosen. Furthermore, the polycarbonate melt was rheologically characterized and used as input material parameters in our simulations. Based on the membrane hypothesis and stabilization algorithms like DEVSS (discrete elastic viscous stress splitting), the specific numerical scheme is derived and the algorithm implementation is summarized. Finally, a complete numerical example of oblique stretching is demonstrated and compared with symmetric stretching. Based on the simulation results, the evolution of thickness and the influence of the y-direction stretching on thickness uniformity are further investigated.

The advances in Li-ion batteries (LIBs) for energy storage continuously face major challenges like acquiring high performance, stability and safety. A separator plays major role for safety and performance of batteries through its porous structure and interaction with electrolyte. In this work, a suitable microporous structure of ultra-high molecular weight polyethylene/poly(4-methyl-1-pentene) (UHMWPE/PMP) blend film via sequential biaxial stretching is achieved by tuning PMP content. The incorporation of PMP leads to high porosity and wettability enabling a significant increase of air permeability, electrolyte uptake and ionic conductivity. A low shrinkage, of 0.7% in transverse direction and 1.6% in machine direction, is observed after exposing PM2 (the film with 7.5 wt% of PMP) at 120°C for 1 h indicating the high thermal stability. Most importantly, a cell containing PM2 presents an excellent electrochemical performance. The discharge capacity reaching 172.8 mAh/g and efficient stable cycling with 99.89% as coulombic efficiency during 100 cycles are obtained at 0.1 and 1 C-rate, respectively. Apart from existing blend separators, current work provides an alternative of using UHMWPE/PMP blend films and deepens the understanding of the role of porous structure for the design of LIBs with best performance in future.

Aethina tumida is a parasite and predator of honeybee causing severe loss to the bee industry. No effective and environmentally friendly methods are available to control this pest at present. Chemosensory genes play key roles in insect behavior which can potentially be used as targets for developing environmentally friendly pest control agents. In this study, the putative chemosensory genes in antennae and forelegs of A. tumida involved in olfaction or contact chemical communication of adults were investigated using RNA transcriptome sequencing and PCR methods. Based on transcriptomic data, unigenes encoding 38 odorant receptors (ORs), 24 ionotropic receptors (IRs), 14 gustatory receptors (GRs), 3 sensory neuron membrane proteins (SNMPs), 29 odorant binding proteins (OBPs), and 22 chemosensory proteins (CSPs) were identified. The analyses of tissue expression profiles revealed that genes encoding 38 ORs, 13 antennal IRs, 11 GRs, 1 SNMP, 24 OBPs, and 12 CSPs were predominately expressed in antennae. No significant differences in expression levels of these genes were found between males and females. Genes encoding 5 non-NMDA iGluRs, 3 GRs, 2 SNMPs, 5 OBPs, and 12 CSPs were predominately expressed in forelegs. RT-PCR assays for SNMPs, OBPs and CSPs further revealed that 3 OBPs (AtumOBP3, 26 and 28) and 3 CSPs (AtumCSP7, 8 and 21) were highly expressed in antennae. Our results enrich the gene inventory of A. tumida and facilitate the discovery of potential novel targets for developing new pest control measures.

To deal with the drinking water safety caused by fluoride, a novel carboxylated polyacrylonitrile nanofibrous membrane (C-PAN NFM) is designed and fabricated massively for the first time by adopting synchronously biaxial stretching and carboxylation. The C-PAN NFM is composed of the layered stack structure by cross-linked nanofibers. Due to its high specific surface area, excellent hydrophilicity, a large amount of carboxyl and amine groups, C-PAN NFM owns high fluoride adsorption capacity and outstanding selectivity. Both the carboxylation and acid treatment of C-PAN NFM improved the fluoride adsorption capacity remarkably. Specifically, C-PAN NFM shows excellent reusability without secondary pollution. The fluoride adsorption behavior of C-PAN NFM is dominated by chemical adsorption, and the adsorption mechanism is mainly driven by hydrogen bonding and ion exchange. The mass-produced C-PAN NFM is a novel polyacrylonitrile-based porous membrane that shows a great application potential for fluoride removal with good efficiency and recyclability.

The structural evolutions of linear low-density polyethylene (LLDPE) are investigated by in-situ synchrotron radiation wide-angle X-ray diffraction (WAXD) during tensile deformation over a wide strain rates range from 0.005 to 250 s−1. The phase transition mechanism is discussed by combining the phase diagram in 2D true stress (σtrue)-strain rate ( e ˙ ) space with the evolutions of several micro-structural parameters, such as the crystallinity (χc), crystal sizes (L110, L200) and lattice parameters (aO, bO). The true stress space can be roughly divided into three regions by two critical true stresses at the onset formation of the monoclinic (σM-onset) and the hexagonal (σH-onset) crystals. In region I where only orthorhombic crystals exist, lattice distortion under the effects of stress plays a dominant role. In region II, the martensitic transformation from orthorhombic to monoclinic crystals occurs and monoclinic crystals load the main tensile stress. In region III, stress-induced melt recrystallization occurs and hexagonal crystals appear. In addition, the effects of strain rate on the stress-induced melt crystallization and lattice deformation are also discussed. This study on LLDPE films might aid to deepen the understanding of structural evolutions during real post-stretching process.

Extension induced crystallization of γ-irradiated isotactic polypropylene (γ-iPP) was studied with the combination of extensional rheology and in-situ wide-angle X-ray scattering (WAXS). The high gel content and markedly frequency-dependent storage modulus of γ-iPP indicates the occurrence of slight crosslinking accompanied by formation of free branching/dangling chains during irradiation. With WAXS, it is found that an abnormal slowing down of crystallization occurs when engineering stress passes its maximum. Lamellar network built of parent and daughter crystal also appears in this region, where daughter crystallization is commonly frustrated under such strong flow. Further increasing strain, crystallization is accelerated gradually and the acceleration becomes more significant after occurrence of strain-hardening. Interestingly, the orientation of crystal increases monotonically during this process. It is supposed that the difference in relaxation rate of cross-linked network and free branching/dangling chains is the origin of the abnormal deceleration and unique structure morphology.

We developed an interesting route for preparing a poly (acrylamide-co-acrylic acid) (P(AAm-co-AA)) hydrogel microsphere with a coating of Au nanospheres (hydrogel microsphere @ Au nanospheres) through self-assembly based on electrostatic interaction. The fabricated composites could be used as highly sensitive enhanced Raman scattering substrates. The nanogaps between adjacent Au nanospheres were dynamically tuned by volume changes in the hydrogel microspheres in the semiwet state under different pH conditions. At pH 6, the hydrogel microsphere @ Au nanospheres demonstrated highly sensitive SERS with an enhancement factor of 109. The product could detect very low concentrations of analytes up to 10-12M 4-aminothiophenol (4-ATP) molecules. This paper proposes a new method for detecting trace amounts of environmental organic pollutants by dynamically tuning the SERS enhancement in the semiwet testing state.

Adding silica nanofiller in silicone rubber can toughen the matrix 3 orders in terms of fracture energy, which is far larger than most other nanofiller–rubber systems. To unveil the astonishing toughening mechanism, we employ in situ synchrotron radiation X-ray nanocomputed tomography (Nano-CT) technique with high spatial resolution (64 nm) to study the structural evolution of silica nanofiller in silicone rubber matrix at different strains. The imaging results show that silica nanofiller forms three-dimensional connected network, which couples with silicone chain network to construct a double-network structure. Stress-induced phase separation between silica nanofiller and silicone polymer chain networks is observed during tensile deformation. Unexpectedly, though the spatial position and morphology of nanofiller network changes greatly at large strains, the connectivity of nanofiller network shows negligible reduction. This indicates that nanofiller network undergoes destruction and reconstruction simult...

A setup of blown film machine combined with in situ synchrotron radiation X-ray diffraction measurements and infrared temperature testing is reported to study the structure evolution of polymers during film blowing. Two homemade auto-lifters are constructed and placed under the blown machine at each end of the beamline platform which move up and down with a speed of 0.05 mm/s bearing the 200 kg weight machine. Therefore, structure development and temperature changes as a function of position on the film bubble can be obtained. The blown film machine is customized to be conveniently installed with precise servo motors and can adjust the processing parameters in a wide range. Meanwhile, the air ring has been redesigned in order to track the structure information of the film bubble immediately after the melt being extruded out from the die exit. Polyethylene (PE) is selected as a model system to verify the feasibility of the apparatus and the in situ experimental techniques. Combining structure information provided by the WAXD and SAXS and the actual temperature obtained from the infrared probe, a full roadmap of structure development during film blowing is constructed and it is helpful to explore the molecular mechanism of structure evolution behind the film blowing processing, which is expected to lead to a better understanding of the physics in polymer processing.

Temperature effects on deformation behaviors of extracted ultrahigh molecular weight polyethylene (UHMWPE) precursor fibers are studied with the in situ synchrotron radiation wide-angle X-ray scattering technique (WAXS) during tensile deformation at temperatures from 25 to 130 °C. The structural and mechanical evolution behaviors during tensile deformation can be divided into four temperature regions with boundaries located at temperatures of αI and αII relaxations and the onset of melting, respectively, which reveal that the deformation behaviors of polymer crystals are determined by the interplay between intrinsic structural dynamic or chains mobility and external stress field. Irrespective of temperature, yield and strain-softening proceed via partial melting while crystal slip via cutting crystal planes occurs in the strain-hardening zone. Finally we construct morphological diagrams containing crystallinity, crystal size, and orientation in temperature–strain space, which may serve as a roadmap for UH...

We device a relaxed lattice model (RLM) to study the mechanism of glass transition, which unifies the cage-effects from particle-particle interaction and entropy. By analyzing entropy in RLM with considering the influence of interactions on equilibrium, we demonstrate that glass transition is a second-order phase transition. For a perfect one-dimensional linked particle system like linear polymer under normal pressure, the free volume at glass transition is rigorously deduced out to be 2.6%, which provides a theoretical basis for the iso-free volume of 2.5% given by Willian, Landel and Ferry (WLF) equation. Extending to system with dead particles linked with higher dimensions like branched or cross-linked chains under positive or negative pressure, free volume at glass transition is varied, based on which we construct a phase diagram of glass transition in the space of free volume-dead particle-pressure. This demonstrates that free volume is not the single parameter determining glass transition, while either dead particles like cross-linked points or external force fields like pressure can vary free volume at the glass transition.

Bimodal ultra-high-molecular-weight polyethylene (UHMWPE)/high-density polyethylene (HDPE) in-reactor blends (IRBs) are produced by the bimetallic catalysts, which are synthesized through co-supporting silylchromate and vanadium-oxide-based catalysts on silica or alumina, zirconia and titania-modified silica. After support modification, the activities of the catalysts for ethylene polymerization are substantially enhanced. The IRBs produced by the modified catalysts also contain more UHMWPE and low-molecular-weight polyethylene (LMWPE) fractions, and have much broader molecular weight distribution (MWD). The homogeneous nature of the IRBs is preliminarily confirmed by the differential scanning calorimetry melting curves, showing unique melting peak in both nascent and recrystallized states. The rheological results reflect that the viscosity of the IRBs is reduced more or less when compared with UHMWPE. The distinct elastic dominance of the IRBs is also observed, implying the UHMWPE characteristics in the IRBs. In addition, the intimate mixing of the IRBs is further verified by the similar slopes of Han curves for the polyethylene (PE) samples. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3404–3412

Young’s modulus of biaxially oriented polypropylene (BOPP) films prepared with homemade film stretcher was investigated, which can be used to indicate the softness of films. It was found that the modulus of films was decreased by about 69% as the content of polyethylene (PE) added into polypropylene (PP) reached 30%. Also, increasing draw temperature can induce lower stress level during stretching, which may lead to the formation of crystals with low orientation level and thus decreased modulus of films. Based on laboratory study, BOPP films produced on commercial line were studied by differential scanning calorimetry (DSC), wide and small-angle X-ray scattering (WAXS, SAXS) with varying contents of PE. SAXS results show that the crystals are oriented in both machine direction (MD) and transverse direction (TD), and the crystals are more oriented in TD than MD according to the WAXS results for all films. Also, the orientation parameter of crystal along TD increases from 0.68 to 0.83 as the contents of PE increase from 0% to 25%. Meanwhile, the modulus of films in MD declines with increase of PE contents generally, improving the film softness. Orientation of crystals is thus an effective structure parameter to adjust the film softness. The relationship of processing-structure-property is also established.

With a combination of extensional rheology and in-situ small-angle X-ray scattering measurements, the protocol of two-step extension is proposed to investigate the early stage of flow-induced crystallization (FIC) in supercooled isotactic polypropylene melt at 138 °C. After both step strains, the crystallization half-time presents a nonmonotonic dependence on the interval time between two extensional operations, based on which three different stages of structural evolution are defined. In stage I, both nucleation and chain relaxation occur, which enhances the crystallization rate but reduces the final lamellar crystal orientation. In this stage, each part of the melt is considered to have approximately the same dynamics to respond homogeneously to the second extension and thus the system is still dominated by a chain-network. When entering into stage II, the sparse large-scaled crystal is formed to construct a heterogeneous crystal-network superimposed on the chain-network, which decelerates the second ex...

Using a pressuring and shearing device (PSD), we explored the simultaneous effects of pressure and flow on β-crystal formation. Interestingly, pressure plays a versatile role in β-crystal formation in isotactic polypropylene (iPP) mixed with β-nucleating agent (β-NA) when a flow field exists simultaneously. At a low pressure (5 MPa), a mass of β-crystals can be obtained over the entire range of applied shear rates (0.0–24.0 s–1). As the pressure increases (50–100 MPa), a weak shear flow (3.2 s–1) can profoundly suppress the β-crystal formation. When elevating the pressure to 150 MPa, β-crystals cannot be generated. The pressure and flow window to produce β-crystals in iPP mixed with β-NA were successfully summarized for the first time. The diversified β-crystal formation behaviors in iPP mixed with β-NA under the simultaneous effects of pressure and shear flow were well elucidated by combining classical nucleation theory and the growth of different crystalline phases. Our current work lays a solid foundat...

With a combination of homemade temperature jump extension apparatus and in-situ synchrotron radiation small and wide angle X-ray scattering (SR-SAXS and SR-WAXS) measurements, uniaxial stretching experiments of polypropylene films at 50 °C-150 °C are carried out to obtain the structure evolution routes. Three distinct features of the structure evolution are observed in temperature space, which can be described with three different deformation models, namely amorphization, crystalline block slip and melt recrystallization, respectively. Also, a refined morphology diagram in strain-temperature space is given to specify the morphology under two dimensional stretching parameter space. This work supplies a guidance for selecting processing conditions to obtain optimal structures after uniaxial stretching in industry.

The mechanical response of fluoroelastomer F2314 under uniaxial extension and its relation with strain-induced structural change are investigated by mechanical analysis, in-situ small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS). Yielding of samples followed by strain hardening is found without necking. Meanwhile, the strain range of strain softening is short, which is 0.77 at 25 °C and 0.3 at 60 °C. Microscopically, solution-cast F2314 shows microphase separation and low crystallinity. Results of WAXS and SAXS indicate strain-induced formation of fibrillar crystal during strain hardening. Based on these findings, it is supposed that the fast relay between destruction of microphase separated domains and formation of fibrillar crystal is the origin of the unique mechanical response.

Melt processing of commercial ultrahigh molecular weight polyethylene (UHMWPE, Mη > 106 g/mol) is an insurmountable bottleneck due to the extremely high melt viscosity arising from its numerous chain entanglements. In the current work, we demonstrated that a UHMWPE (Mη = ∼3.4 × 106 g/mol) with a highly linear structure and low entanglements synthesized by a single–active–site Ziegler–Natta catalyst can be melt injection molded without the aid of any additives and, more strikingly, structurally manipulated by means of an intensive shear flow during the packing stage of injection molding. Therewith, large amounts of self-reinforced superstructures, i.e. shish-kebabs and oriented lamellae, were generated in bulk UHMWPE. Appealing interlocked shish-kebabs appeared due to the overstocked shishes that made the epitaxial kebabs penetrate into each other. The self-reinforced superstructures, together with the eliminated structural defects and the increased crystallinity, brought about considerable mechanical enhancement. In particular, the yield strength and ultimate tensile strength of structured linear disentangled UHMWPE were increased by 75% and 71%, from 23.3 ± 0.2 and 40.4 ± 0.6 MPa for compression-molded counterpart to 40.8 ± 1.3 and 69.0 ± 0.8 MPa, respectively. Our current effort makes a pivotal breakthrough in efficient fabrication of high-performance UHMWPE parts, holding a great prospect towards the application in severe conditions and the instructive effects on synthesis in return.

Crystallinity distribution of natural rubber around filled micrometer-size glass beads under different strains are studied with in-situ micro-focused scanning X-ray diffraction (μ-SXRD), where the glass beads are taken to serve as a model of filler. The experimental results suggest, due to the gradient stress field around the glass bead, the oscillatory distribution of crystallinities around the glass bead tends to form soft-hard double network with multi-scale hierarchical structures and spontaneously responds to external strains. The double network spreads stress in larger region and avoids stress concentration, in which the hard domains with high crystallinities effectively sustain the external stress while the soft domains with low crystallinity store elastic energy. According to the equal strain and equal stress conditions, the quantitative calculation on enhancement factor indicates that the soft-hard double network structure can increase the fracture energy to about three orders of magnitude as comparing to that of structure with homogeneous distribution of crystallinity.

The sequence and coupling of intra- and interchain orderings in flow-induced crystallization (FIC) of partially cross-linked isotactic polypropylene (iPP) is studied with in situ Fourier transform infrared spectroscopy (FTIR) and synchrotron radiation X-ray scattering techniques, which reveal that multiscale structural intermediates emerge prior to the onset of crystallization. Upon imposing flow, intrachain conformational ordering or coil–helix transition (CHT) occurs first, which is directly correlated with external stress. As helical content is built up at large strain, density fluctuation happens, and sufficient long helices may result in orientation ordering before FIC. The results demonstrate that stress induced intrachain CHT is the essential structural intermediate in FIC, which can be further coupled with interchain orientation and density providing either helical content or length meets the criterions for the phase transitions. We propose that coupling among external stress, intrachain conformat...

A free standing 2D PS colloidal crystal with Au nanoshells/hydrogel composite film (CAuHCF) was fabricated by embedding a 2D PS colloidal crystal with Au nanoshells into a polyacrylic acid (PAA) hydrogel film. This CAuHCF can act as a visualized sensor with high diffraction intensity. The 2D PS colloidal crystal with Au nanoshells was prepared by depositing an Au layer on PS colloidal crystal obtained by interfacial self-assembly. The diffraction intensity of the CAuHCF was increased by about 30-fold than that of traditional 2D PS colloidal crystal/hydrogel composite film on transparent substrate due to large scattering cross section of Au shell. Such sensors based Au nanoshells array with the simple preparation process and the strong diffraction signal are promising ones for practical applications in visual detection. Additionally, with the simple preparation process and high diffraction intensity, other visualized sensors based different hydrogel matrix and the 2D PS colloidal crystal with Au nanoshells could be synthesized for monitoring various analysts.

Polyacrylic acid-grafted ultrahigh molecular weight polyethylene (UHMWPE-g-PAA) fibers were prepared by radiation-induced grafting of acrylic acid onto UHMWPE porous fibers and were examined for Cu2+ removal from aqueous solutions. The developed fibers were characterized using Fourier transform infrared spectroscopy, mechanics test, scanning electron microscopy and energetic dispersive spectroscopy analysis. It was demonstrated that the UHMWPE fibers were modified successfully with grafted acrylic acid, which conferred excellent hydrophilic performance to UHMWPE porous fibers. The mechanics test indicated that considerable mechanical strength (~0.4 GPa) still reserved for the UHMWPE-g-PAA fibers in spite of somewhat radiation degradation. The high-strength, hydrophilic and porous natures render UHMWPE-g-PAA fibers promising as economical adsorbent in wastewater treatment. Prepared under different radiation dose and different degree of grafting of polyacrylic acid (PAA), the adsorption kinetics of the UHMWPE-g-PAA fibers was investigated using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The results reveal a large adsorption capacity of 63 mg g−1 for the UHMWPE-g-PAA fibers and the adsorption behavior follows perfectly a pseudo-second-order kinetics model regarding the Cu2+ solution adsorption.

We report diverse meso-phase arrangements of supra-molecular nanotubes assembled by ionic benzene-1,3,5-tricarboxamide (BTA) molecules in water; their transition pathway and equilibrium structure are controlled by the helical structure. Besides, the different sensitivity to the condition of initial solutions is revealed for the final rectangular phase and the intermediate phase.