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The molting hormone 20-hydroxyecdysone (20E) plays a key role in insect development, metamorphosis, and reproduction. Previous studies have shown that ecdysteroid metabolism is regulated by a series of CYP genes in most of the insect species. However, the roles of these CYP genes in a Coleopteran beetle, Aethina tumida (small hive beetle, SHB) have not yet been explored.In the current study, we identified seven CYP genes (six Halloween genes and one AtCYP18A1 gene) related to 20E metabolism. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) showed that AtCYP307A1 and AtCYP307B1 were primarily expressed in the embryonic stage and in the cephalothorax of larvae. RNA interference (RNAi) screening revealed that suppression of AtCYP307A1 expression caused a lethal phenotype during the larval-pupal metamorphosis. Furthermore, Hematoxylin and Eosin staining of the integument showed that the RNAi of AtCYP307A1 inhibited the apolysis and degradation of the old cuticle. In addition, silencing of AtCYP307A1 resulted in significant down-regulation of 20E titers and the expression levels of 20E signaling pathway genes. Finally, the AtCYP307A1 RNAi phenotype was rescued by topical application of 20E.Our studies suggest that AtCYP307A1 involved in 20E synthesis is indispensable during the larval-pupal metamorphosis of beetles, which could serve as a putative insecticide target for pest control. © 2022 Society of Chemical Industry.

Summary Thermo-responsive polymeric metamaterials have become indispensable because of their wide applications to human-machine interaction, soft robots, wearable devices, augmented/virtual reality, etc. Polymer network-regulated sensing materials could present higher flexibility and adaptability compared to those with rigid structures or silicon-based materials, and their responses to thermal stimulation are more easily triggered and implemented compared to other stimuli, such as light, electricity, etc. Progress relies on the development of programmable materials with tunable thermal expansion on the micro-/macroscale, sheds light on this direction, and facilitates devices that exhibit unprecedented adaptation, sensitivity, and agility. and facilitates devices that exhibit unprecedented adaptation, sensitivity, and agility. This review refines the perceptual elements of positive, negative, anisotropic, tunable, and zero thermal expansion behaviors of polymers and further summarizes corresponding mechanisms, materials design, tuning methods, and related applications to flexible perceptual devices, including 2D response as sensor, 2D/3D/4D response as actuator, and insensitive response as stabilizator. The framework of research progress is presented from a single perceptual element to an integrated perceptual system, from microscopic regulation to macroscopic response. We present an overview of the current research status, which will be an important guide for future development in this field, and simultaneously provide a reference for the broader scientific community.

The cyanobacterium Arthrospira platensis plays a unique role in the food industry and is a promising and valuable natural source of bioactive compounds. The culture density of A. platensis should be further increased to improve biomass production and productivity, resulting in high conversion efficiency and reducing the cost of production. In this work we utilize a series of methods to increase the biomass yield from 2.26 to 21.57 g L−1. By screening live algae filaments and removing dead algal mass via filtration before cultivation, the biomass production increased from 2.26 to 2.77 g L−1. Using response surface monitoring methodology to optimize the light intensity and initial culture density further improved biomass production to 5.97 g L−1. We also evaluated the feasibility of fed-batch and turbidostatic cultivation for enhancing biomass production of A. platensis GMPA7. The results showed that fed-batch cultivation can increase the biomass production to 15.56 g L−1. Finally, turbidostatic cultivation can further improve the biomass production to 21.57 g L−1, which is a more than eightfold increase compared to the starting culture. Therefore, the turbidostatic cultivation strategy can be further exploited for large-scale and long-term cultivation.

Cellulose acetate (CA) based films are widely used in liquid crystal displays due to their outstanding transparency, and a certain orientation birefringence of CA films is required when they are used as retardation films. The regulation of orientation birefringence is usually from the perspective of stretch-induced orientation, while the effects of crystallization behaviors of CA films remain obscure. In this study, the roles of crystallization and orientation on the orientation birefringence of CA films were elucidated. For cellulose diacetate films, the orientation birefringence is dominated by the orientation degree. In comparison, apart from the orientation degree, crystallinity is another key variable to regulate the orientation birefringence of cellulose triacetate and plasticized cellulose triacetate films, originating from the birefringence heterogeneity of the crystalline and amorphous phases. These results provide valuable guidelines for the production of CA-based optical films with excellent optical performance.

The sun (∼6,000 K) and outer space (∼3 K) are two significant renewable thermodynamic resources for human beings on Earth. The solar thermal conversion by photothermal (PT) and harvesting the coldness of outer space by radiative cooling (RC) have already attracted tremendous interest. However, most of the PT and RC approaches are static and monofunctional, which can only provide heating or cooling respectively under sunlight or darkness. Herein, a spectrally self-adaptive absorber/emitter (SSA/E) with strong solar absorption and switchable emissivity within the atmospheric window (i.e., 8 to 13 μm) was developed for the dynamic combination of PT and RC, corresponding to continuously efficient energy harvesting from the sun and rejecting energy to the universe. The as-fabricated SSA/E not only can be heated to ∼170 °C above ambient temperature under sunshine but also be cooled to 20 °C below ambient temperature, and thermal modeling captures the high energy harvesting efficiency of the SSA/E, enabling new technological capabilities.

Structural transitions of polyamide 46 (PA46) films during the tensile stretch at temperatures from 37 to 249 °C were studied using in situ synchrotron radiation wide-angle X-ray diffraction (SR-WAXD) and Fourier transform infrared (FTIR) techniques. The structural evolution during the stretch at different temperatures can be roughly divided into three regions. In region I (37 ≤ T < 180 °C), stretch enlarges the d-spacing gap between the (100) and (010/110) planes of α phase (triclinic), which is opposite to that during heating. In region II (180 ≤ T < 230 °C), stretch induces a reverse Brill transition, which is characterized by the single diffraction of γ phase (pseudohexagonal) splitting into two diffractions of α phase, while further increasing the strain drives the two split diffractions to transform to a single broad diffraction. As in situ FTIR measurements reveal the continuously increasing content of trans conformation, we speculate that stretch may induce a new form, which is an intermediate structure close to both α and γ phases (named α′ phase) at large strain. In region III (230 ≤ T ≤ 249 °C), the γ phase may skip the α phase and directly transform into the α′ phase. The nonequilibrium crystal phase diagrams of PA46 were constructed in the strain–temperature space and true stress–temperature space. Current results demonstrate that stretch plays a countereffect of heating on the Brill transition of PA46.

Numerical experiments on phase field modeling of the fracture in pre-strained hyperelastic materials reveal that the classical mechanical-based dynamic phase field model is ineffective in the framework of non-linear deformation. The aspiration to gain insight into rapid fracture instability motivated us to develop a novel dynamic phase field model characterized by wave velocity invariance, enabling crack propagation at a velocity approach to the asymptotic limit. Given that the numerical treatment of rapid fractures involves extremely high spatiotemporal resolution, robust explicit dynamics and a tried-and-tested multi-level hybrid adaptive mesh algorithm are invoked. More crucially, an original adaptive distorted mesh removal scheme (ADMR) was developed to cope with the intractable finite element mesh distortion problem in large deformation fractures. The detailed numerical implementation for entire procedures is outlined, and its reliability is verified by two quasi-static fracture benchmarks. Utilizing the proposed model and innovative algorithms, the arresting ultrahigh-speed crack oscillation and tip-splitting instabilities captured in the fracture experiments of brittle gels were successfully reproduced. The critical crack velocity at the onset of the instability is also identified, close to the experimental measurements.

Polymer chains in both dilute solutions and melts undergo cyclic rotation and retraction, which is known as tumbling, under steady shear flow. However, it is still not known how the individual molecules in melts rotate freely under the constraints caused by surrounding chains. In this work, a Brownian dynamics simulation is used to investigate the influences of the interchain interactions on the polymer chain motions in both dilute solutions and melts under steady shear flow. Compared with previous simulation studies, a greater number of similarities and differences between tumbling in dilute solutions and melts are addressed, and the results explicitly suggest the critical role of the entanglements in melts during shear flow. Three components of the gyration radius in different directions [flow direction ( ⟨ R g x 2 ⟩ ), gradient direction ( ⟨ R g y 2 ⟩ ), and vorticity direction ( ⟨ R g z 2 ⟩ )] are shown to exhibit different dependencies on the shear rate depending on whether dilute solutions or melts are being examined. However, the characteristic tumbling times τ r in both cases are proportional to γ ˙ − 2 / 3. The distributions P ( T ) of time T that the chains spend in each tumbling cycle show that both states exhibit an exponential decay of P ( T / τ r ) in the high- T region. In the low- T region, P ( T / τ r ) in the melts with variable shear rates are coincident with each other, while P ( T / τ r ) in dilute solutions show different shapes. With respect to the distributions of chain orientation, both cases show the same scaling relationships for shear rates and chain lengths. Based on these findings, main conclusions are as follows. The entanglements still restrict the evolutions of polymer chain configurations despite the number of entanglements decreasing with increased flow strength. The tumbling motion in melts can occur inside the tube, and the chain behaviors inside the confining tubes are rather similar to those in dilute solutions.

By employing a variational phase field model, we investigated the dynamic brittle fracture of poly (methyl methacrylate) (PMMA) through computer simulation. Without the explicit fracture criterion, current simulations not only successfully reproduced the crucial experimental observations on crack propagation, such as crack patterns, velocity evolutions and limit crack velocity but also discovered some new features not reported in the experimental study yet. Through quantifying the energy flux into the crack tip and fracture energy, we observed that the crack bifurcation of PMMA always occurs with the energy flux into the crack tip exceeding a critical value and proposed that crack bifurcation obeys an energy criterion. Based on this criterion, the long-standing challenge of limit crack velocity in experiments is successfully predicted by continuum theory, which unveils that crack bifurcation sets the upper limit for crack velocity. Combining the crack bifurcation criterion and continuum theory provides a rational explanation for complex path selection of cracks.

Stretch-induced crystallization (SIC) and structural transitions of poly(dimethylsiloxane) (PDMS) filled with different contents of nanosilica were studied with an in situ synchrotron radiation wid...

Strain-induced crystallization (SIC) in polybutadiene rubber (BR) was studied by in situ synchrotron radiation wide-angle X-ray diffraction (SR-WAXD) over a broad temperature range (-90 °C → 25 °C). Depending on the presence or absence of SIC and quiescent crystallization temperature, three temperature regions are divided. Detailed structural evolution is summarized in the strain-temperature space. Based on this micro-structural evolution information, the macroscopic mechanical response of BR, together with poly(isobutylene-isoprene) rubber (IIR) and natural rubber (NR), is reproduced based on Flory's and Plagge's theories. The origins of the mismatch of calculated and experimental stress-strain curves, especially in the large strain region, are discussed, and are mainly ascribed to the micro-macro connection approach and the network inhomogeneity.

The stretch-induced structural evolution mechanism is a long-standing scientific question in the post-stretching processing of polymer films. X-ray scattering, especially a combination of small- and wide-angle X-ray scattering (SAXS/WAXS), provides a powerful method to study the hierarchical structure of polymer films. Recent advances in synchrotron radiation (SR) light sources and detection techniques allow one to measure the structural evolution of polymer films during post-stretching processing in real time with ultrahigh time resolution, which benefits the understanding on this topic. This review summarizes some recent investigations on post-stretching processing of polymer films, which combine in situ X-ray scattering techniques with purposely designed tensile apparatus in terms of three aspects: uniaxial stretching, biaxial stretching and stretching with chemical reactions. Concerning the polymer bulk, traditional deformation mechanisms like stretch-induced crystallization (SIC), crystal slipping, phase transition and melting-recrystallization are discussed for the uniaxial and biaxial post-stretching of polymer films. New deformation models have been developed to focus on the structural evolution on the length scale of lamellar stacks, which consider the potential microphase separation of the interlamellar amorphous phase and microbuckling. For solution systems, the coupled effects of the mechanical work from external force and the chemical potential from possible chemical reactions are taken into account for the structural evolution during stretching in solution. Roadmaps of structural and morphological evolution in the processing parameter space (i.e., temperature, stress, strain and the concentration of additive in the bath solution) are eventually constructed for precursor films. The accumulation of a structural evolution database for post-stretching processing of polymer films can be expected to provide a helpful guide for industrial processing for high-performance polymers in the near future.

The hierarchical structural evolution of natural rubber (NR) filled with different contents of nanoscale carbon black (CB) (10 phr-CB10 and 50 phr-CB50) after first loading and recovering for different times was investigated by X-ray nano-CT, wide-angle X-ray scattering (WAXS) and solid state NMR techniques. The CB filler structures as captured by X-ray nano-CT recover gradually with increasing recovering time, but the filler network with different CB contents shows dramatically different structure evolution. For CB10, limited by the filling content, CB particles mainly induces a hydrodynamic effect in spite of deformation or recovering. For CB50, the CB filler forms a 3D connected network, partially destructed during deformation, and the destructed part can be partially recovered during recovery. This suggests that the connected CB filler structure mainly acts as a network reinforcement, whereas the destructed part can induce a hydrodynamic effect. The different effects induced by different CB filling contents are also reflected by the NR matrix, which is reflected by the onset strains εc of strain-induced crystallization (SIC) of NR as captured by WAXS. For CB10, εc remains almost constant, i.e. εc = ca. 1.49, while that of NR with CB50 slightly decreases from initial ca. 1.12 to 0.96 with increasing recovering time up to 50 h. Also, the bound rubber fraction and entangled rubber network remain unchanged after deformation and under different recovery time as detected by the magic sandwich echo (MSE) FID and proton multiple quantum (MQ) NMR. These results demonstrate the key role of the CB filler network in determining the stress-softening behavior of reinforced rubber.

U, Sr, Pb, Nd, and Hf isotope ratios can provide basic and important information of nuclear materials. We established a simple and efficient column chemistry method using nano-NaBiO

A biaxial stretching device is designed and developed for the real-time structural measurements of polymer films. This device adopts a vertical layout to perform real-time x-ray scattering measurements. It has a maximum stretching ratio of 8 × 8 in two perpendicular directions. Its maximum experimental temperature and stretching rate are 250 °C and 100 mm/s, respectively. The control accuracies of the experimental temperature and stretching rate are ±1 °C and 0.01 mm, respectively. All the parameters related to film biaxial processing, such as stretching speed, stretching ratio, and temperature, can be independently set. The device feasibility is demonstrated via a real-time experiment in a synchrotron radiation beamline. Wide-angle x-ray diffraction, small-angle x-ray scattering, and stress–strain data can be simultaneously obtained during various stretching modes. The proposed device fills the gap between the synchrotron radiation x-ray scattering technique and the biaxial stretching processing of polymer films. This device will play an important role in improving the understanding of the physics behind biaxial polymer processing.

The general aspects of polymer crystallization under external flow, i.e., flow-induced crystallization (FIC) from fundamental theoretical background to multi-scale characterization and modeling results are presented. FIC is crucial for modern polymer processing, such as blowing, casting, and injection modeling, as two-third of daily-used polymers is crystalline, and nearly all of them need to be processed before final applications. For academics, the FIC is intrinsically far from equilibrium, where the polymer crystallization behavior is different from that in quiescent conditions. The continuous investigation of crystallization contributes to a better understanding on the general non-equilibrium ordering in condensed physics. In the current review, the general theories related to polymer nucleation under flow (FIN) were summarized first as a preliminary knowledge. Various theories and models, i.e., coil–stretch transition and entropy reduction model, are briefly presented together with the modified versions. Subsequently, the multi-step ordering process of FIC is discussed in detail, including chain extension, conformational ordering, density fluctuation, and final perfection of the polymer crystalline. These achievements for a thorough understanding of the fundamental basis of FIC benefit from the development of various hyphenated rheometer, i.e., rheo-optical spectroscopy, rheo-IR, and rheo-x-ray scattering. The selected experimental results are introduced to present efforts on elucidating the multi-step and hierarchical structure transition during FIC. Then, the multi-scale modeling methods are summarized, including micro/meso scale simulation and macroscopic continuum modeling. At last, we briefly describe our personal opinions related to the future directions of this field, aiming to ultimately establish the unified theory of FIC and promote building of the more applicable models in the polymer processing.

Cost-effective, representative and spatial coverage sampling designs are required to monitor the effects of potentially toxic elements (PTEs) in the soil. This study aims to evaluate the minimum sample sizes and placement of soil sampling designs to monitor and characterize the spatial variation of the PTEs (Cu, Zn, Cd, Cr, Pb, and Ni) in the soils. However, there is no standardized approach for evaluating the optimum soil sample size and monitoring location because of the spatial heterogeneity of PTEs in the soil. As a result, three broad techniques were applied. The first step was to use Global Moran's I and q-statistic values to describe the variability of soil PTEs and select appropriate evaluation methods. Second, using simple random sampling (SRS), ordinary kriging (OK), and Mean of Surface with Non-homogeneity (MSN), we estimated and evaluated soil PTEs in the current soil sampling schemes. Finally, MSN and spatial simulated annealing (SSA) optimization techniques were used to assess the required sample sizes and placements in the existing designs. Method performance was evaluated using a standard error (SE) and a relative standard error of the mean (RSE). Except for Zn and Cd, all PTEs tested showed heterogeneous distributions over the area. The MSN lowered the predicted SE by 79-86 % compared with SRS. The OK approach also outperformed the SRS method regarding mean estimated values of soil PTEs by 42-57 %. After SSA refined the initial design, the predicted SE by MSN of Cr and Zn was lowered by 13 % and 39 %, respectively. The MSN was effective with small sample sizes, reducing sample sizes and surveying costs by 39 % after SSA optimized the existing sample numbers. Thus, integrating various sampling strategies may be efficient for building optimal sample designs to monitor PTEs in the soil.

We study the process e^+e^− → π^+π^−ηγ, where the photon is radiated from the initial state. About 8000 fully reconstructed events of this process are selected from the BABAR data sample with an integrated luminosity of 469 fb^(-1). Using the π^+π^−η invariant mass spectrum, we measure the e^+e^− → π^+π^−η cross section in the e^+e^− center-of-mass energy range from 1.15 to 3.5 GeV. The cross section is well described by the Vector-Meson dominance model with four ρ-like states. We observe 49±9 events of the J/ψ decay to π^+π^−η and measure the product Γ_(J/Ψ → e^+e^−)B_(J/Ψ → π^+π^−η) = 2.34 ± 0.43_(stat) ± 0.16_(syst) eV.

We analyze the molecular mechanism of the chain stretching and orientation for the stress overshoot response of linear and comb polymers under shear using the nonequilibrium molecular dynamics simulation. Different from the strain overshoot behavior of linear polymers, the shear stress peak strain γ max of comb polymers vs the Rouse–Weissenberg number W i R = τ R γ ˙ displays three scaling law regions, in agreement with previous experimental results [F. Snijkers et al., ACS Macro Lett. 2, 601–604 (2013)]. In contrast to experiments, our simulations visually reveal the stretching and orientation dynamics of chain segments at the stress overshoot. According to the detailed information of stretching and orientation of the segment with different lengths, it is found that the size of a tension blob decreases with increasing W i R, and it follows a power-law with an exponent of −0.6 for a linear system. With respect to the comb systems, the size of a tension blob decreases accordingly with grafting density under the same shear rate. Unambiguous molecular pictures at the stress overshoot are also given at different shear rates for linear and comb polymers.We analyze the molecular mechanism of the chain stretching and orientation for the stress overshoot response of linear and comb polymers under shear using the nonequilibrium molecular dynamics simulation. Different from the strain overshoot behavior of linear polymers, the shear stress peak strain γ max of comb polymers vs the Rouse–Weissenberg number W i R = τ R γ ˙ displays three scaling law regions, in agreement with previous experimental results [F. Snijkers et al., ACS Macro Lett. 2, 601–604 (2013)]. In contrast to experiments, our simulations visually reveal the stretching and orientation dynamics of chain segments at the stress overshoot. According to the detailed information of stretching and orientation of the segment with different lengths, it is found that the size of a tension blob decreases with increasing W i R, and it follows a power-law with an exponent of −0.6 for a linear system. With respect to the comb systems, the size of a tension blob decreases accordingly with grafting...

One prerequisite for the large-scale application of biodegradable polymers is the manipulation of macroscopic performances of commercially available biopolymers during processing according to diffe...

The influences of both temperature and external flow field on film blowing have been studied with a combination of a custom-built film blowing device and in situ synchrotron radiation small- and wide-angle X-ray scattering techniques. Polyethylene (PE) with different structural topologies, namely linear (MPE) and long-chain branched polyethylene (LPE), was used here with different responses to temperature and flow. The MPE film shows a spherulite-like superstructure with low orientation independent of take-up ratio (TUR), while the LPE has a typical row-nucleated structure at high TUR. But for LPE film obtained at low TUR, it exhibits the combination of both crystal morphologies. Further analysis of the microscopic structural evolution of PE during film blowing by synchrotron X-ray scattering reveals three different types of network evolution: (i) the temperature-induced crystallization (TIC) dominated process (MPE); (ii) the flow-induced crystallization (FIC) dominated process (LPE with high TUR); and (i...

A dramatically improved, uniform distribution of commercial ultrahigh molecular weight polyethylene (UHMWPE) with high-density polyethylene (HDPE) via solution blending, rather than that of melt blending, is often apparent in experimental investigation. Recently, we demonstrated that a UHMWPE/HDPE blend created by in-reactor polymerization with a Cr/V bimetallic catalyst supported on modified silica can obtain an even better molecular chain distribution while saving energy and solution costs, even more so than experiments using a solution blend. Furthermore, by gel-spinning processing, an abundance of hierarchical, interlocking shish-kebab crystals were generated in the in-reactor polymerized blend fibers (IRBFs), exhibiting better mechanical properties than those of solution blend fibers (SBFs). The tensile strength of the IRBFs increased by about 20% under the same draw ratio, since the interlocking shish-kebab structures contributed to homogenous deformation. The two kinds of fibers exhibit high crystallinity and have a highly oriented shish-kebab structure. Compared with the SBFs, the IRBFs inclined to form longer shish features and smaller kebab sizes, and the draw process was more conducive to the transformation of kebab to shish structures. Thus, the IRBFs can obtain an excellent hierarchal network structure, benefiting more from the hot-stretching process. Our work lays a solid foundation for the efficient fabrication of high-performance UHMWPE/HDPE fibers as well as the optimization of an original polyethylene catalyst system.

Theoretical approaches addressing the mechanism of polymer crystallization remain the great challenge in polymer science. Numerous different, or even conflicting, models/theories have been proposed...

Design of tough hydrogels has made great progress in the past two decades. However, the synthetic tough gels are usually much softer than some biotissues (e.g., skins with modulus up to 100 MPa). Here we report a new class of ultrastiff and tough supramolecular hydrogels facilely prepared by copolymerization of methacrylic acid and methacrylamide. The gels with water content of approximately 50–70 wt % possessed remarkable mechanical properties, with Young’s modulus of 2.3–217.3 MPa, tensile breaking stress of 1.2–8.3 MPa, breaking strain of 200–620%, and tearing fracture energy of 2.9–23.5 kJ/m2, superior to most existing hydrogels, especially in terms of modulus. Typical yielding and crazing were observed in the gel under tensile loading, indicating the forced elastic deformation of these hydrogels in a glassy state, as confirmed by dynamic mechanical analysis. The ultrahigh stiffness was attributed to the dense cross-linking and reduced segmental mobility caused by the robust intra- and interchain hydr...

The crystal structure evolution of polyethylene (PE) gel films containing paraffin oil are studied with wide-angle X-ray scattering (WAXS) during sequentially biaxial stretching at the temperature around the melting point. Also, the surface morphologies of films after biaxial stretching are characterized by scanning electron microscope (SEM). During machine direction (MD) stretching process, the crystal structure is transformed from lamellar stacks to fibrillar crystals through melting recrystallization. While for transverse direction (TD) stretching, there exist three kinds of deformation mechanisms determined by draw ratio in MD (λMD), i.e., transformation of weakly oriented crystals into fibrillar crystals by melting recrystallization at small λMD; with moderate λMD, the fibrillar crystals in MD are tilted towards TD; at larger λMD, the microfibrils are teared into thinner ones or fibrillar crystals, inclining to TD. Finally, the crystal morphology diagram is summarized in two-dimensional (2D) strain space, serving a roadmap for processing of PE microporous membranes.

The relationship between the macroscopic non-linear mechanics and the microscopic crystal structural evolution of pre-oriented high-density polyethylene (HDPE) is investigated by in situ synchrotron radiation wide-angle X-ray diffraction (WAXD) measurement over a wide temperature range from −10 to 130 °C. With the concept of stress-induced disordering of crystal, the ratio ( φ a / b ) of lattice parameters a to b is defined as a new structural variable, which can reflect the lattice distortion and then the microscopic stress state of orthorhombic crystal (O-crystal). According to the temperature-dependent non-linear variation of φ a / b with strain, the contributions of O-crystal and monoclinic crystal (M-crystal) to the macroscopic mechanics including linear elasticity, yielding, stress softening and strain hardening are clarified. It is found that M-crystal bears the main extensional stress once formed, although it survives within a limited strain window relying on temperature. By further combining the extensional phase diagram constructed in strain-temperature space, the HDPE deformation is recognized to undergo successively one-dimensional (1D) chain segments rotation of crystal, two-dimensional (2D) crystal plan shearing or slipping and three-dimensional (3D) recrystallization along with increasing strain or stress, demonstrating a multiscale structural transition and energy dissipation mechanism.

The structural evolution of poly (ethylene terephthalate) (PET) with distinct water absorption during uniaxial deformation slightly above glass transition temperature (Tg) were investigated by in-situ synchrotron radiation wide angle X-ray scattering (WAXS). Results show that the locally ordered structures are not conducive to stretch-induced crystallization (SIC) although the corresponding entropy is more close to crystals compared to random chains, which is due to the limited chain mobility therein. The “frozen orders” should be destroyed to achieve the critical chain mobility required by SIC even with the presence of water as plasticizer. Unexpectedly, absorption of water does not enhance but suppresses SIC though it does promote the chain mobility, originating from lower stress level with higher water contents. Stress and chain mobility directly correlate with chain stretch and orientation in positive and negative manners, respectively, demonstrating that chain stretch and orientation also play important role in SIC around Tg.

Combining a homemade uniaxial stretching device and the simultaneous in-situ synchrotron radiation WAXS measurement, the structural evolution during transverse direction (TD) stretching of machine direction (MD) pre-stretched Poly(ethylene terephthalate) (PET) film has been investigated. Current work reveals that increasing the MD pre-stretch before the occurrence of stretch induced crystallization (SIC) can enhance the crystallization and orientation in TD stretching. The concept of parallel chains structures (PCS) cross-linked network is proposed to interpret the rubber-like mechanical behavior. An appropriate stretch ratio window in stretching above the glass transition temperature (Tg) is existed, where the PCS cross-linked network before crystallization can be induced by stretching above Tg. With the help of the PCS cross-linked network, the chain orientation is retained more effectively under stretching, promoting the formation of subsequent crystallization and crystal cross-linking network. The strain hardening in different pre-stretched samples occurs accompanied by the same crystallinity and various chains orientation. This demonstrates that the strain hardening is determined by the crystal cross-linked network rather than the orientation. Current work supplies a guidance for getting the improved film products of PET with enhanced comprehensive mechanical properties, process stability and higher chain orientation.