Above the glass transition temperature, the stretch-induced instability of the amorphous phase in semicrystalline polymers is usually accompanied by cavitation. However, the early-stage mechanism of cavitation remains unclear and remains to be debated, owing to the hierarchical structure and the limitations of time-resolved experimental methods in probing the pores, particularly at the subnanoscale. In this study, we chose hard-elastic polypropylene (HEPP) as a model system to simplify the structural hierarchy of semicrystalline polymers and enable a focused investigation on the lamellar stack scale. Benefiting from our newly developed positron annihilation lifetime spectroscopy (PALS) apparatus with a super-high counting rate, combined with a specifically designed tensile machine, we successfully tracked the real-time evolution of subnanoscale free-volume pores in HEPP during continuous tensile loading. During macroscopic yield, we directly observed the growth (increase in average size), coalescence (reduction in number density), and redistribution (transition from unimodal to bimodal size distributions) of the free-volume pores. By integrating in situ PALS data with in situ small-angle X-ray scattering (SAXS) and volumetric strain measurements, we find that our stress-induced microphase separation is a more suitable explanation for the deformation instability of amorphous phase and volume increase in HEPP compared to other traditional models. In this nonequilibrium process, the voids on the scale of tens of nanometers originate from pre-existing free-volume pores in the amorphous phase and represent the ultimate state of the free-volume-rich microphases within unstable lamellar clusters.

Designing nonprecious and highly efficient HER electrocatalysts is a challenging but crucial task. Through first-principles structure search calculations, we have identified two-dimensional (2D) Co2Si and Co2Ge materials containing planar hypercoordinated Si/Ge. Further, based on these two fascinating structures, a series of additional TM2X (X = Si and Ge) monolayers with the hypercoordinated Si/Ge are also obtained by screening 3d, 4d, and 5d transition metal atoms. Almost all of these 2D monolayers can exhibit high thermodynamic, dynamical, thermal, and mechanical stabilities, as well as inherent metallicity. Among them, a total of nine monolayers, including planar, quasi-planar, or buckled TM2Si (TM = Co, Fe, Pd, and Pt) and TM2Ge (TM = Co, Ni, Fe, Pd, and Ir) systems, can uniformly present high HER catalytic activity. Particularly, the Co2Si, Co2Ge, and Ni2Ge monolayers containing the planar hypercoordinated Si/Ge can exhibit considerably high HER catalytic activity over a wide range of theta H* coverages (even up to 3ML). Their active site density can reach as high as 3.471 x 10(15) to 4.341 x 10(15) site per cm(2), surpassing many reported materials and even Pt. A related analysis of the catalytic mechanism has been conducted. These remarkable findings can be beneficial for the future realization of excellent HER catalysts.

A stretching apparatus capable of conducting tensile tests over a broad strain rate range (10-3-250 s-1) and a wide temperature range (-75-250 °C) has been designed for polymeric materials, in particular the polymeric films. Specifically, this stretching apparatus can be combined with in situ ultrasmall-, small-, and wide-angle x-ray scattering (USAXS/SAXS/WAXS) measurements. The sample stretching is achieved through the synchronized rotation of rolls, powered by servo motors. The output electrical signal extracted from a torque sensor, when combined with the rotational speed of rolls and initial sample dimensions, enables the determination of the relationship between engineering stress (σ) and Hencky strain (ε). With the sample chamber and precise control loop, the prescribed temperature can be achieved using either hot airflow for heating or cold liquid nitrogen flow for cooling. By integrating this stretching apparatus with a high brilliance x-ray source at beamline BL10U1 in Shanghai Synchrotron Radiation Facility (SSRF) and detectors featuring ultrafast acquisition rates, it becomes possible to monitor multiscale structure evolutions of polymeric samples under harsh conditions involving high-speed loading combined with varying temperatures.

The microstructure evolution of semicrystalline poly(vinyl alcohol) (PVA) during drying within a wide temperature window ranging from 95 to 50 degrees C was captured in situ by synchrotron radiation X-ray scattering (SRXS), specifically small- and wide-angle X-ray scattering. A portable film-casting apparatus with a high-pressure reactor was designed and manufactured. Its high safety features, coupled with its detachable and installable design, facilitate its integration with SRXS for researching the drying process of polymer solutions. The time-resolved microstructure parameters, such as the crystallinity and lamellar thickness, as well as the water fraction during the PVA film formation process help us to elucidate four sequential regimes during drying: (1) regime I, the evaporation stage, where the water evaporates at a constant rate without any crystallization occurring; (2) regime II, the rapid-crystallization stage, where PVA crystallinity increases dramatically and the long period declines rapidly due to the evaporation of the water in the interlamellar amorphous layer; (3) regime III, the diffusion-limited stage, where the PVA chain mobility and diffusion of water in the amorphous layers are gradually hindered as the PVA concentration increases, resulting in a slowdown of the decline in the long period; (4) regime IV, the annealing stage, during which the long period exhibits a secondary rapid reduction with the insertion of new-formed lamellae into the lamellar stacks. The synergistic and competing effects of the temperature and water fraction significantly influence the crystallization kinetics and chain mobility: lowering the temperature results in an increasing supercooling degree but a decrement of chain mobility as evidenced by low-field NMR experiments, where the former facilitates the nucleation but the latter impedes the crystallization kinetics. The above effects lead to a nonmonotonic temperature-dependent onset PVA weight fraction (omega(PVA)) of crystallization at the very beginning of regime II.

Understanding the deformation and fracture behaviors of amorphous polymers, particularly those toughened via dynamic bonds, is crucial for their practical applications and further material design. In this study, the amorphous plasticized poly(vinyl butyral) (p-PVB) is chosen as a model system, characterized by heterogeneous distribution of hydrogen bonds, strong dynamical asymmetry, and exhibiting stretch-induced phase separation. Through measuring and examining the time-temperature superposition principle on viscoelastic modulus in dynamic mechanical analysis (DMA) tests, hysteresis energy in loading-unloading tests, rupture work in uniaxial tensile tests, and fracture toughness in pure shear tests across broad strain rate and temperature ranges, we have specifically elucidated the critical roles of bulk viscoelasticity and stretch-induced phase separation on the energy dissipation during the deformation and fracture of p-PVB. In p-PVB, the stretch-induced phase separation makes a significant contribution to its fracture energy dissipation, retards crack propagation, and enlarges the fracture strain. The systematic investigations in this work not only enable the prediction of the mechanical behaviors and energy dissipation pathway of p-PVB products, such as the interlayer films used in laminated glass, but also provide guidance for designing amorphous polymers with similar structures and great energy dissipation capability during deformation and fracture.

The BiOIO3/BiOCl heterojunctions with different dominated facet, BiOIO3/{110}BiOCl and BiOIO3/{001} BiOCl, were prepared through facile solvothermal/hydrothermal methods with ethylene glycol/deionized water as solvents. As. prepared BiOIO3/BiOCl photocatalysts were characterized by X-ray diffraction, scanning electron microscope, energy. dispersive spectroscopy, and UV-Vis diffuse reflectance spectra. The photocatalytic activity of BiOIO3/BiOCl heterojunctions was evaluated by photo-catalytically decomposing rhodamine B and phenol in an aqueous solution under visible light irradiation. The results showed that 25% BiOIO3/{110}BiOCl heterojunctions exhibited the highest photocatalytic efficiency. The degradation of RhB over 25% BiOIO3/{110}BiOCl was 98.7% after 15 min of light irradiation. And 100% phenol can be degraded after irradiation for 150 min. The better photocatalytic performance of BiOIO3/{110}BiOCl may be attributed to the strong absorption of the visible light, the heterojunction structure, and the efficient separation of photo-generated carriers benefiting from the dominated (110) facet of BiOCl. The superoxide radicals (center dot O-2(-)) and holes (h(+)) are the main active species in the photocatalytic pro. cess. Moreover, a reasonable mechanism for enhanced photocatalytic performance was also discussed based on the experimental results.

High-throughput DFT calculations are performed to explore the oxygen evolution reaction (OER) catalytic activity of a series of 2D graphene-based systems with TMO3 or TMO4 functional units. By screening the 3d/4d/5d transition metal (TM) atoms, a total of twelve TMO3@G or TMO4@G systems had extremely low overpotential of 0.33 ti 0.59 V, in which the V/Nb/Ta atom in VB group and Ru/Co/Rh/Ir atom in VIII group served as the active sites. The mechanism analysis reveals that the filling of outer electrons of TM atom can play an important role in determining the overpotential value by affecting the DGO* value as an effec-tive descriptor. Especially, in addition to the general situation of OER on the clean surface of the systems containing the Rh/Ir metal centers, the self-optimization process of TM-sites was carried out, and it made most of these single-atom catalysts (SAC) systems to have high OER catalytic activity. All these fascinat-ing findings can contribute to an in-depth understanding of the OER catalytic activity and mechanism of the excellent graphene-based SAC systems. This work will facilitate the design and implementation of non-precious and highly efficient OER catalysts in the near future. (c) 2023 Elsevier Inc. All rights reserved.

Using the newly developed positron annihilation lifetimespectroscopy(PALS) facility with a high count rate up to 3000 cps, insitu PALS experiments were performed for the first time onthe continuous stretching process of polymers to quantitatively analyzethe minute-scale evolution of free-volume holes. According to thestress-strain relationship and PALS results of four types ofpolyethylenes with different crystallinities, the tensile processcould be divided into four distinct stages: elastic, initial nonlinear(until yield point), postyield, and strain hardening stages. The increaseof o-Ps (orthopositronium) lifetime in the first three stages exhibitsan enlargement of free-volume hole size with increasing strain. Thedecrease of the o-Ps lifetime in the last stage is most probably dueto the increasing anisotropy of free-volume holes. The relative fractionalfree volume FFVr (derived from hole radius R (calculated from the Tao-Eldrup model) and o-Ps intensity)generally increases in the first two stages but remains nearly unchangedin the other two stages. This work demonstrates a new feasibilityto disclose minute-scale evolution of microstructure of materialsthrough in situ PALS experiments in the future.

Peridynamic is a promising nonlocal continuum theory that reconstructs the equations of motion of solid mechanics using spatial integral equations, rendering it suitable for describing objects with discontinuities such as cracks. In this study, a novel extended ordinary state-based peridynamic model was developed for nonlinear deformation and fracture analysis, which established a general relationship with continuum-based parameters and permitted the selection of different influence functions. Based on the principle of virtual displacement, the complete derivations of the peridynamic parameters were presented for two and three-dimensional conditions. After that, the specific numerical scheme and algorithm implementation were summarized. The capability and accuracy of the proposed nonlinear model were verified by comparing with the experimental and finite element simulation results. Finally, several other numerical examples were provided to further demonstrate the applicability and robustness of the proposed model and its implementation.

The structure-property relationship of the interlamellar amorphous phase in semicrystalline polymers has been a fundamental yet controversial topic in polymer physics for several decades. The intricate hierarchical structure and limited availability of experimental techniques pose significant challenges in quantitatively characterizing the evolution of the amorphous structure and establishing its connection to the mechanical behavior. In this work, the unannealed and annealed isotactic polypropylene hard-elastic films composed of idealized series-arranged lamellar stacks are studied to simplify the mechanical coupling between the two phases. By utilizing the synchrotron-based in-situ small and wide-angle X-ray scattering (SAXS/WAXS) techniques, the apparent modulus and overall volumetric strain of the amorphous phase are estimated. Moreover, with our significant progress in the counting rate of positron annihilation lifetime spectroscopy (PALS), the minute-scale structure evolution of amorphous phase (free-volume pores) during the tensile process is now feasible to be captured. Combing in-situ X-ray scattering and in-situ PALS results, in the elastic regime, it is found that triaxial stress in the amorphous phase leads to the expansion of free-volume pores (about 23% volume increase for the annealed sample, 35% volumetric strain for the unannealed one) and density decrement within occupied volume by overcoming Van Der Waals force. Our quantitative analysis also reveals that the annealing process not only enhances the crystallinity and aspect ratio of lamellae but also weakens the intrinsic modulus and chain packing density of amorphous phase.

As a key component in laminated glass, plasticized polyvinyl butyral (PVB) interlayer is a kind of impact-resistant polymer material with high toughness. Recently, by using ultrasmall angle X-ray scattering (USAXS) technique, Stretch-induced phase-separated structure on the scale of hundreds of nanometers formed in plasticized PVB for the first time is reported. In this work, the multiscale relaxation behavior of plasticized PVB is further investigated. The relaxation behavior of deformed plasticized PVB is studied from macroscopic stress, mesoscopic phase-separated structure, and microscopic chain segment by combining USAXS, and birefringence with in situ stretching device. The contributions of chain segments and hydrogen bonding clusters for the multiscale relaxation behavior are discussed.

The well-received phase-field method smears the discrete cracks in the damaged bands, blurring the explicit crack tip. However, identifying the location of the crack tip is sometimes vital. The widely used scheme at present considers the forefront of a phase-field contour as the crack tip. Such a method, to our best knowledge, is inapplicable for branched cracks, which motivates us to develop a novel stepwise identification strategy for multi-branched crack tips termed si-MCT. Instead of searching for crack tips globally, the proposed si-MCT realizes this in the chosen deliberately local regions (searching regions), and then automatically updates these regions as the cracks propagate. For the robust implementation of si-MCT, a novel concept of active crack tip zone is also proposed to cope with the extreme circumstances where adjacent crack paths are too close to interfere with identifying the crack tip. Furthermore, the core algorithms and specific procedures of the proposed strategy are also elaborated. Moreover, several representative tests are studied, showing the bright prospect of si-MCT in dynamic multi-branch crack tracking and adaptive mesh algorithm.

Dopant-free, electron donor (D)–acceptor (A) type, polymeric hole-transporting materials (HTMs) possess excellent film formability and hole transport properties, which ensure high efficiency, stability, and reproducibility to the PVSCs. Compared with benzothiadiazole (BT), benzotriazole (BTA) was less incorporated into polymeric HTMs. Herein, two indacenodithieno[3,2-b]thiophene (IDTT)-BTA copolymers BT-T and BT-TT containing different π-bridge of thiophene and thienothiophene, are synthesized and studied. BT-T bearing thiophene π-bridge presents decent coplanarity, higher hole mobility, and better interface morphology than its sister polymer BT-TT. The PVSC with dopant-free BT-T displayed a peak power conversion efficiency (PCE) of 17.1% and remained above 85% of its initial PCE for more than 30 days at ambient conditions. In view of the rare report on the BTA-based polymeric HTMs, this work will cast lights on further exploration of high-efficiency D-A polymeric HTMs.

Under DFT calculations, a systematic investigation is carried out to explore the structures and oxygen evolution reaction (OER) catalytic activities of a series of 2D single-atom catalyst (SAC) systems, which are constructed by doping the transition metal (TM) atoms in group VIII into the cavities of rigid phthalocyanine carbide (pc-C3N2). We can find that when Co, Rh, Ir and Ru atoms are doped in the small or large cavities of a pc-C3N2 monolayer, they can be used as high-activity centers of OER. All these four new TM@C3N2 nanostructures can exhibit very low overpotential values in the range of 0.33~0.48 V, even smaller than the state-of-the-art IrO2 (0.56 V), which indicates considerably high OER catalytic activity. In particular, the Rh@C3N2 system can show the best OER performance, given that doped Rh atoms can uniformly serve as high-OER-active centers, regardless of the size of cavity. In addition, a detailed mechanism analysis was carried out. It is found that in these doped pc-C3N2 systems, the number of outer electrons, the periodic number of doped TM atoms and the size of the embedded cavity can be considered the key factors affecting the OER catalytic activity, and excellent OER catalytic performance can be achieved through their effective cooperation. These fascinating findings can be advantageous for realizing low-cost and high-performance SAC catalysts for OER in the near future.

Wrinkles are commonly observed in uniaxially stretched hyperelastic membranes and eventually disappear with the increase of stretching. The widely used scheme at present assumes the material parameters to be empirical values and straightforwardly considers some constitutive models to explore the wrinkling and restabilization behavior. However, this simple treatment may cause deviation from experiment by ignoring the applicability of the models and the authenticity of the input parameters, prompting us to report based on realistic material parameters. This paper presents an experimental, theoretical and numerical investigation on the wrinkling and restabilization behavior of hyperelastic materials. By fitting experimental stress-strain curves of PDMS films, we confirm that the 3-term Ogden model bears a closer resemblance to the experimental data than the widely used neo-Hookean, Mooney-Rivlin, and Arruda-Boyce models under certain circumstances. The simulation results indicate that different constitutive models quantitatively affect the critical buckling strain, wrinkling amplitudes, and restabilization points. Furthermore, the isolated central bifurcation point solved by Koiter stability theory agrees well with the simulation and experimental results. A 3D phase diagram of stability boundaries was established to gain a comprehensive insight into the effects of geometric parameters (length, width, and thickness) on wrinkling.

Solid-stated smart polymers responsive to external stimuli have attracted much attention for potential application in the field of photoelectron devices, logic gates, sensor, data storage and security. However, it is a bigger challenge for polymers than that for small molecules in solid state to acquire stimuli-responsive properties, because polymers with high molecular weight are not as easy to change the packing structure as small molecules under external stimulation. Here, a D-A type alternating copolymer PTMF-o containing 3,4-bisthienylmaleimide (A unit) and fluorene (D unit) is designed and synthesized. Upon irradiation of sunlight, PTMF-o film exhibits a photo-response with the color altering from purple to colorless. It is attributed to the structure of copolymer transformed from ring-opening form (PTMF-o) to ring-closure form (PTMF-c), resulting from the oxidative photocyclization of 3,4-bisthienylmaleimide unit. Consequently, the ability of charge transfer (CT) from fluorene to 3,4-bisthienylmaleimide unit in PTMF-o can be easily weakened by light stimuli. PTMF-o film displays a WORM-type resistive storage performance for the strong CT. Interestingly, after exposure, the electrical memory behavior in situ transfers into FLASH type, due to weak CT in PTMF-c. PTMF-o film can also be employed as smart material to construct NAND and NOR logic gates by using light as input condition. The work provides a simple way to modify the electronic properties of polymers and realize stimuli-response in solid states.

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.

In comparison with the common-used electron donor (D)-electron acceptor (A) type symmetric polymers with regular structures, their asymmetric counterparts have received much less attention and seldom been applied in polymer solar cells. Since the precise modulation of pi bridge can significantly influence the photoelectric properties of D-A type polymers, pi bridges of tailorable thiophenes are introduced into benzodithiophene (BDT)-benzodithiophene-4,8-dione (BDD) copolymers in both symmetric and asymmetric patterns. Together with the halogen substituent of fluorine or chlorine on BDT, four polymer donors are designed and synthesized. As expected, PTB2T-F and PTB2T-Cl with the asymmetric pi bridges of thiophene and hexyl-bithiophene exhibit better planarity, stronger intermolecular interaction and higher hole mobility than P2TB2T-F and P2TB2T-Cl with the symmetric pi bridges of hexyl-bithiophene. The more suitable phase separation and optimized nanomorphology is determined by the reasonable miscibility between asymmetric polymer and acceptor, which is evaluated by Flory-Huggins interaction, contributing to the extremely higher performance than that of symmetric counterpart. Moreover, paired with IT-4F as the acceptor, PTB2T-F affords better device performances than the reference BDT-BDD polymer PM6 with the symmetry pi bridge of thiophene. These results demonstrate that the precise modulation of asymmetric pi bridges is a promising strategy to construct high-efficiency D-A type polymer donors.

The copolymerization of ethylene and different α-olefins could result in polyethylene (PE) with different structural topologies, and lead to polyethylene products with different macroscopic performances. Herein, three different polyethylene samples, namely low-density polyethylene (l-PE), metallocene catalyzed ethylene-hexene copolymer (h-PE) and ethylene-octene copolymer (o-PE), were selected as representatives to construct the structure-process-property relationship during film blowing. The detailed crystal-based network evolution during film blowing was first characterized by in-situ synchrotron radiation X-ray scattering. The crystallization process of l-PE film is determined by the coupling effects of temperature and flow, while those of h-PE and o-PE films are dominated by the temperature. Furthermore, the hierarchical crystal structure from the molecular scale to micrometers of final films and segmental dynamics were systematically characterized by multiple ex-situ characterization techniques, i.e. Solid-State NMR, FTIR, SEM. l-PE film shows the crystalline morphology of the row-nucleated structure, whereas h-PE and o-PE show spherulite-like superstructure with better mechanical properties. The current study tentatively constructs the relation of primary chemical structure, microstructural evolution and macroscopic performances of different polyethylene copolymers during film blowing.

Using density functional theory (DFT) combined with nonequilibrium Green's function investigates the electron-transport properties of several molecular junctions based on the [2,5']bipyrimidinyl(biphenyl isocyanide)gold(I) molecule (BPM-Au(I)CN-BP), which is modified by one to three alkyl groups forming BPM-Au(I)CN-BP(CH2)(n). The asymmetric current-voltage characteristics have been obtained for the molecular junctions. Rectifying performance of Au/S-BPM-Au(I)CN-BP-S/Au molecular junction can be regulated by introducing alkyl chain. The M-1 molecular junction exhibits the best rectifying effect. Its maximum rectifying ratio is 2109, which is about 150 times more than that of the molecular junction based on the original M. Moreover, all the systems modified by alkyl group have obvious negative differential resistance behavior (NDR). The current-voltage (I-V) curves of all the systems in this work are illustrated by transmission spectra.