Showing papers by "Liangbin Li published in 2021"

Simultaneously Toughening and Stiffening Elastomers with Octuple Hydrogen Bonding.

Abstract: Current synthetic elastomers suffer from the well-known trade-off between toughness and stiffness. By a combination of multiscale experiments and atomistic simulations, a transparent unfilled elastomer with simultaneously enhanced toughness and stiffness is demonstrated. The designed elastomer comprises homogeneous networks with ultrastrong, reversible, and sacrificial octuple hydrogen bonding (HB), which evenly distribute the stress to each polymer chain during loading, thus enhancing stretchability and delaying fracture. Strong HBs and corresponding nanodomains enhance the stiffness by restricting the network mobility, and at the same time improve the toughness by dissipating energy during the transformation between different configurations. In addition, the stiffness mismatch between the hard HB domain and the soft poly(dimethylsiloxane)-rich phase promotes crack deflection and branching, which can further dissipate energy and alleviate local stress. These cooperative mechanisms endow the elastomer with both high fracture toughness (17016 J m-2 ) and high Young's modulus (14.7 MPa), circumventing the trade-off between toughness and stiffness. This work is expected to impact many fields of engineering requiring elastomers with unprecedented mechanical performance.

Superior lithium battery separator with extraordinary electrochemical performance and thermal stability based on hybrid UHMWPE/SiO2 nanocomposites via the scalable biaxial stretching process

Abstract: As a vital part of lithium-ion batteries (LIBs), the separator is closely related to the safety and electrochemical performance of LIBs. Despite the numerous membranes/separators available commercially, their thermal stability and service life still severely limit the efficiency and reliability of the battery. Herein, for the first time, we designed and prepared a hybrid ultra-high molecular weight polyethylene (UHMWPE)/silicon dioxide (SiO2) nanocomposite membrane via a sequential biaxial stretching process. SEM, EDS, ATR-FTIR, WAXS and TGA characterizations offer clear evidence for the successful preparation of UWMWPE-SiO2 nanocomposite membranes. The influence of SiO2 on the structure and properties of UHMWPE membranes was systematically investigated. The presence of SiO2 improves various fundamental properties of UHMWPE separators, such as thermal stability, electrolyte uptake and wettability, ionic conductivity, and electrochemical performance. Thus, obtained lithium-ion batteries have an excellent discharge capacity of 165 mAh g−1 at 0.1 C-rate and 123 mAh g−1 at 5 C-rate and a greater cycling performance over 100 cycles. Thus, this investigation delivers inspiration for the expansion of inorganic-organic nanocomposite separators for next-generation lithium-ion batteries.

A Unified Thermodynamic Model of Flow-induced Crystallization of Polymer

Abstract: We propose a unified thermodynamic model of flow-induced crystallization of polymer (uFIC), which incorporates not only the conformational entropy reduction but also the contributions of flow-induced chain orientation, the interaction of ordered segments, and the free energy of crystal nucleus and crystal morphology. Specifically, it clarifies the determining parameters of the critical crystal nucleus size, and is able to account for the acceleration of nucleation, the emergence of precursor, different crystal morphologies and structures induced by flow. Based on the nucleation barrier under flow, we analyze at which condition precursor may occur and how flow affects the competition among different crystal forms such as orthorhombic and hexagonal phases of polyethylene. According to the uFIC model, the different crystal morphologies and structures in the flow-temperature space have been clarified, which give a good agreement with experiments of FIC.

Inducing nano-confined crystallization in PLLA and PET by elastic melt stretching

Abstract: Based on the widely studied poly(l-lactic acid) (PLLA) and polyethylene terephthalate (PET) that are brittle in their fully crystalline form, this Letter shows that they can be made to be super ductile, heat resistant and optically clear by creating nano-sized crystals while preserving the entanglement network. Atomic force microscopic images confirm the perceived nano-confined crystallization. Time-resolved X-ray scattering/diffraction measurements reveal the emergence of cold crystallization during either stress relaxation from large stepwise melt-stretching or annealing of pre-melt-stretched PLLA and PET above Tg. Mechanical tests show that these polymers in such a new state are rigid even well above Tg, e.g., at 100 °C.

Anomalous thermally expanded polymer networks for flexible perceptual devices

Abstract: 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.

Mixed displacement-pressure-phase field framework for finite strain fracture of nearly incompressible hyperelastic materials.

Abstract: The favored phase field method (PFM) has encountered challenges in the finite strain fracture modeling of nearly or truly incompressible hyperelastic materials. We identified that the underlying cause lies in the innate contradiction between incompressibility and smeared crack opening. Drawing on the stiffness-degradation idea in PFM, we resolved this contradiction through loosening incompressible constraint of the damaged phase without affecting the incompressibility of intact material. By modifying the perturbed Lagrangian approach, we derived a novel mixed formulation. In numerical aspects, the finite element discretization uses the classical Q1/P0 and high-order P2/P1 schemes, respectively. To ease the mesh distortion at large strains, an adaptive mesh deletion technology is also developed. The validity and robustness of the proposed mixed framework are corroborated by four representative numerical examples. By comparing the performance of Q1/P0 and P2/P1, we conclude that the Q1/P0 formulation is a better choice for finite strain fracture in nearly incompressible cases. Moreover, the numerical examples also show that the combination of the proposed framework and methodology has vast potential in simulating complex peeling and tearing problems

Study of the process e+e- →φη at center-of-mass energies between 2.00 and 3.08 GeV STUDY of the PROCESS ... ABLIKIM M. et al

Abstract: The process $e^{+}e^{-} \rightarrow \phi\eta$ is studied at 22 center-of-mass energy points ($\sqrt{s}$) between 2.00 and 3.08 GeV using 715 pb$^{-1}$ of data collected with the BESIII detector. The measured Born cross section of $e^{+}e^{-} \rightarrow \phi\eta$ is found to be consistent with {\textsl{BABAR}} measurements, but with improved precision. A resonant structure around 2.175 GeV is observed with a significance of 6.9$\sigma$ with mass ($2163.5\pm6.2\pm3.0$) MeV/$c^{2}$ and width ($31.1_{-11.6}^{+21.1}\pm1.1$) MeV, where the first uncertainties are statistical and the second are systematic.

Numerical study on oblique stretching of viscoelastic polymer film

Abstract: 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.

Study of e+e- →π0X (3872)γ and search for Zc (4020)0 →x (3872)γ

Abstract: Using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.178 to 4.600 GeV, we study the process $e^+e^-\rightarrow\pi^{0}X(3872)\gamma$ and search for $Z_c(4020)^{0}\rightarrow X(3872)\gamma$. We find no significant signal and set upper limits on $\sigma(e^+e^-\rightarrow\pi^{0}X(3872)\gamma)\cdot\mathcal{B}(X(3872)\rightarrow\pi^{+}\pi^{-}J/\psi)$ and $\sigma(e^+e^-\rightarrow\pi^{0}Z_c(4020)^{0})\cdot\mathcal{B}(Z_c(4020)^{0}\rightarrow X(3872)\gamma)\cdot\mathcal{B}(X(3872)\rightarrow\pi^{+}\pi^{-}J/\psi)$ for each energy point at $90\%$ confidence level, which is of the order of several tenths pb.