ISSN 1000-3304CN 11-1857/O6
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Progress in Photo-initiated Living Graft Polymerization of Biomaterials
Li-wei Sun, Ling-jie Song, Shi-fang Luan, Jing-hua Yin
三校 , doi: 10.11777/j.issn1000-3304.2020.20198
[Abstract](532) [FullText HTML](161) [PDF 2349KB](6)
Surface modification of biomaterials via graft polymerization has become one of the most important methods to enhance their virtual bio-functionalities. Compared with other living graft polymerization methods, photo-initiated living graft polymerization exhibits superior merits and has been more and more widely used in surface modification of biomaterials. The photoinitiators used for photo-initiated living graft polymerization are mainly categorized into three types: photoiniferter-mediated polymerization (PIMP), benzophenone and its derivatives, and thioxanthones. In this review, the development, graft mechanism and characteristics of the three photo-initiated living graft polymerization systems are briefly introduced. Meanwhile, the applications of photo-initiated graft polymerization in three different biomedical fields are mainly reviewed. i) Antibacterial surface: layered functional polymer brushes constructed by photo-initiated living graft polymerization have been developed to achieve antibacterial function on demand; ii) Immunoassay: layered functional polymer brushes can solve the problem of low detection sensitivity and protein interference; iii) Bioactive molecules fixed on the surface: visible light living graft polymerization system is used to realize the immobilized enzyme on the surface as well as the cell surface modification to improve the stability. Finally, their recent advances in the biomedical fields and the future opportunities and challenges are highlighted.
Synthesis and Mechanical Property Investigation of Epoxy Liquid Crystal Elastomer Material
Hai-feng Lu, Meng Wang, Shuai Huang, Xu-man Chen, Zhi-yang Liu, Hong Yang
三校 , doi: 10.11777/j.issn1000-3304.2020.20197
[Abstract](850) [FullText HTML](602) [PDF 1185KB](3)
Most of the traditional liquid crystal elastomers are based on polyacrylate or polysiloxane systems and prepared by thermal or photo-initiated free-radical polymerization. However, the free-radical polymerization is easily inhibited by oxygen, causing high volume shrinkage and large internal stress during the curing process . In order to address these drawbacks, we design and synthesize a new liquid crystal monomer and a crosslinking agent bearing epoxy groups. The epoxy liquid crystal elastomer is prepared by in situ cationic polymerization/crosslinking using iodonium salt as the photo-initiator. Compared with the traditional liquid crystal elastomers, the volume shrinkage is small during the photo-initiated cationic reaction and the photo-curing process will not be interfered by oxygen. The liquid crystallinity and mechanical properties of the epoxy liquid crystal elastomer material are systematically characterized. The results show that epoxy liquid crystal elastomer material prepared by photo-initiated cationic polymerization possess better mechanical properties than the traditional polyacrylate/polysiloxane liquid crystal elastomers. The elastic modulus reach 2.53 MPa at the temperature beyond the LC-to-isotropic phase transition.
DNA Nano-robot: What Dreams May Come
Wen-Bin Zhang
三校 , doi: 10.11777/j.issn1000-3304.2020.20275
[Abstract](178) [FullText HTML](89) [PDF 687KB](1)
Nano-robots that are capable of entering the human body to cure disease and save life have been a science fiction and a futuristic therapeutic dream. Recently, Baoquan Ding’s group and Guangjun Nie’s group at the National Center for Nanoscience and Technology have made considerable progress in this direction with the development of a DNA nanodevice-based vaccine for cancer immunotherapy. A tubular DNA nanostructure was designed and prepared by first forming a DNA rectangle via DNA origami, precise loading of an antigen and two types of molecular adjuvants, and subsequent tube-closing by low pH-responsive DNA “locking strands” on the edge. When injected subcutaneously, this DNA nanodevice can be delivered efficiently to the draining lymph nodes and accumulates in lysosomes within the antigen-presenting cells. The local acidic subcellular environment triggers the release of the DNA locking strands to expose the vaccine and elicit a potent antigen-specific T-cell response, leading to significant tumor regression and inhibition of tumor reoccurrence in mouse cancer models. Impressively, they also demonstrate strong long-term memory effect of this vaccine against tumor rechallenge. All these features indicate that this DNA nanodevice provides a platform for precise and programmable delivery of molecular medicines. It is a milestone toward fulfilling the dream of the “nanorobot doctor” proposed by Feynman some seventy years ago and holds great promise to transform modern medicine and medical care.
Progress of Differential Scanning Calorimetry and Its Application in Polymer Characterization
Yong-xuan Chen, Dong-shan Zhou, Wen-bing Hu
三校 , doi: 10.11777/j.issn1000-3304.2020.20234
[Abstract](902) [FullText HTML](484) [PDF 3949KB](44)
Differential scanning calorimetry (DSC) is a highly efficient tool to characterize the thermal properties and to investigate thermal reactions of materials owing to its advantages of simplicity and universality as well as the well-defined measurement results with a clear physical meaning. In recent years, the tremendous development of DSC technique has greatly extended the measurement range for polymer characterization, facilitating the further research on thermodynamics and kinetics of physical transitions in polymer materials. Temperature-modulated DSC (TMDSC), a remarkable advance in DSC technique in 1990s, introduces scanning rate perturbation into the traditional linear heating rate so that the overall heat flux could be separated into reversible and non-reversible signals and furthermore, the reversing heat capacity could be measured in the quasi-isothermal process. Fast scanning chip-calorimetry (FSC) is a new progress of DSC technique in recent years, which adopts a miniature chip made of silicon nitride thin films to replace the traditional crucible as the sample holder and temperature controller, thus achieving ultra-fast heating and cooling rates for the measurement with sample mass on micro- and nanogram scale, which makes it possible to analyze the structural reorganization phenomena occurring frequently during temperature scanning and to simulate the actual condition of polymer processing. This review starts with the fundamentals of thermal analysis, followed with a sequential introduction of DSC, TMDSC and FSC by covering their histories, principles, experimental skills as well as their practical examples of polymer characterization. In the end, the prospect of the development and application of DSC are highlighted. We hope this survey would help the readers to gain a deeper understanding of the commonly used DSC technique and encourages them to expand further applications of DSC techniques in polymer characterization.
Toward Correct Measurements of Shear Rheometry
Shuang Liu, Xiao Cao, Jia-qi Zhang, Ying-chun Han, Xin-yue Zhao, Quan Chen
三校 , doi: 10.11777/j.issn1000-3304.2020.20230
[Abstract](994) [FullText HTML](629) [PDF 3557KB](12)
Rheology is an important tool for characterizing polymeric materials. The knowledge of polymer dynamics obtained from rheological measurements can guide the processing of polymeric materials. Nevertheless, it is a challenging task to conduct precise measurements on shear rheometers. First, we summarize the basic assumptions of rheological measurements: (1) the applied strain is on the sample, (2) the stress reflects sample’s own stress response, and (3) the flow field is purely the shear flow. Second, we highlight the conditions under which the above assumptions become invalid, which leads to incorrect measurements. For example, the first assumption is violated when compliance of the equipment or the wall-slip becomes non-negligible, the second assumption is violated when either inertia of the equipment, that of the sample, or the interfacial tension contributes non-negligibly to the overall torque, and the third assumption is violated when there is the secondary flow, shear-banding, or edge fracture. We show some examples of the incorrect measurements owing to these violations of the assumptions. Finally, we stress the importance of good experimental practice in rheological experiments.
Chemical Structure Design, Preparation and Properties of UV Curable Polyimide
Rui Zhao, Yu-ting Fang, Jie Dong, Xin Zhao, Qing-hua Zhang
三校 , doi: 10.11777/j.issn1000-3304.2020.20244
[Abstract](276) [FullText HTML](125) [PDF 1917KB](6)
There is little literature on the development of photocurable polyimide materials and their curing process. Therefore, this paper focuses on the design and preparation of molecular structure of photocurable polyimides (PSPIs) and their composition formula and curing conditions. A soluble polyimide with a high UV curing ability was designed and synthesized by using 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) containing phenolic hydroxyl as the carrier of photosensitive unit and a rigid diamine with a benzimidazole unit to endow the material with good mechanical properties. FTIR and 1H-NMR tests proved the successful preparation of photosensitive polyimides with a maximum GMA content (photosensitive unit) of 51%. The solubility test results showed that the designed PSPIs had an excellent solubility in conventional polar solvents, which is beneficial to the processing of materials. The influences of light source distance, irradiation intensity, type and content of photoinitiator, and type of active diluent on the curing process were systematically investigated, and the composition and curing conditions were summarized (e.g., the distance of the light source was 10 cm, the electric current was 100%, the Irgacure 819 content was 3 wt%, and the active diluent NVP was 20 wt%). The overall properties of photocured polyimide films were analyzed. The tensile strength of the film was up to 123 MPa, and the Td5 and Td10 reached 410 and 487 °C, respectively. The mass residual rate at 800 °C is above 55%. Water contact angle of the cured PI film was up to 90.7°, and the water absorption rate was as low as 0.40 wt%, which indicated the excellent hydrophobicity of the cured PSPI film. Accordingly, the novel photocurable polyimides with excellent overall property developed in present work show great potential in microelectronics application.
Advances of High-voltage Cathode Binders for Lithium Ion Batteries
Zhi Liu, Tian-tian Dong, Huan-rui Zhang, Wei Liu, Guang-lei Cui
三校 , doi: 10.11777/j.issn1000-3304.2020.20207
[Abstract](732) [FullText HTML](417) [PDF 5653KB](6)
Lithium ion batteries (LIBs) generally suffer from severe electrolyte decomposition and the unstable cathode and electrolyte interface (CEI) during high voltage cycling, seriously impeding their practical applications. Binders can not only tightly bind the cathode active materials and conductive carbons onto the current collector, but also play a positive role in the construction of multi-scale compatible CEI. Thus, theoretically, the optimization of binders can effectively solve the above problems. In this review, we present the requirements of high voltage cathode binders, including excellent adhesion and mechanical properties, electrochemical stability and thermal stability, as well as good ion and electron transport capacity, review the high voltage cathode binders reported at present through natural binders and synthetic binders and summarize the recent research progress and development status of binders for high voltage LIBs along with the action mechanisms of various binders on the bonding and coating of electrodes and the performance of LIBs. Furthermore, we elaborate the interactions between the polar groups of binders and the cathode active particles, such as hydrogen bonding and ion dipole interaction. Finally, some perspectives and directions on future development of state-of-the-art binders for high voltage LIBs are discussed.
Numerical Simulation and Experimental Study on Dynamic Heat Build-up of Rubber
Xin-yu Wang, Wei Wang
六校 , doi: 10.11777/j.issn1000-3304.2020.20231
[Abstract](338) [FullText HTML](247) [PDF 1302KB](36)
In order to improve the calculation accuracy of the numerical simulation of rubber dynamic heat build-up, based on the time-temperature equivalence principle, a new method to determine the tensile test conditions taking into account both temperature and strain rate is proposed in this study. It may meet the test conditions of equipment and service conditions of rubber products at the same time. Moreover, in order to obtain more accurate parameters of the hyperelastic constitutive equation, a set of stresses obtained by stress relaxation experiment under the fully relaxed state of rubber is used to fit the hyperelastic model of viscoelastic approach. Based on the mentioned test methods and ABAQUS software, the dynamic compression heat generation finite element models of rubber cylinder are established. Considering the influence of temperature, strain rate and dynamic strain amplitude on the mechanical properties of rubber, the heat build-up calculation method based on loss tangent and hyperelastic model and viscoelastic heat build-up calculation method based on Prony series in frequency domain are respectively used to calculate the compression heat build-up of rubber cylinder. The results show that the temperature rise calculated by the two approaches are in agreement with the experimental results of compression heat build-up, but the viscoelasticity algorithm has higher accuracy, and the heat build-up history predicted agrees well with the experimental results, which can better describe the hysteresis heat build-up phenomenon of rubber, consequently verifying the correctness of the material test conditions proposed in this study.