最新刊期
卷 52 ， 期 4 ， 2021
- 摘要：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.关键词：DNA origami;Molecular machine;Controlled delivery;Cancer vaccine;Immunotherapy
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发布时间：2021-03-05
Research Highlights
- 摘要：In the recent decade, due to their versatile advantages of solution processability, light-in-weight, super flexibility, low thermal conductivity and highly adjustable molecular structures or components, organic and organic/inorganic composite thermoelectric materials as well as their flexible devices have made great progress. A variety of judicious strategies of both material preparation and flexible device assembly have been developed to improve the corresponding thermoelectric performances. Hence, they are very promising for wide application fields, including harvesting of waste heat, flexible electronics, soft robotics and internet-of-things. So far, in all of the reported organic polymer and composite thermoelectric materials, poly(3,4-ethylene dioxyethiophene):poly(styrene sulfonate) (PEDOT:PSS) is probably the most frequently studied and most successful system with the highest thermoelectric performance. Nevertheless, compared with inorganic thermoelectric materials, the thermoelectric properties of PEDOT:PSS is distinctly lower than the maximum value of the inorganic counterparts. Considering the fact of few special reviews about the strategies to effectively enhance the thermoelectric performances for PEDOT:PSS to date, it is timely and urgent to publish a relevant review. Here, we present a summarization of the recent progress in the development of strategies to significantly enhance the thermoelectric properties of PEDOT:PSS developed so far. First, the advances of the doping/de-doping strategies, such as second doping/de-doping, acid or alkali treatment, and treating by ionic liquid, are focused in details. The corresponding mechanism is discussed as well. Then, the recent developments of three types of boosting strategies,i.e. tuning of aggregation structures (including crystalline and orientation microstructures), construction of PEDOT nano-micro structures (for example, nanospheres, nanorods, micro- or nano-tubes and nanofibers), and fabrication of thermoelectric composites with inorganic particles such as carbon nanotubes and graphene nanoplatelets, are concentrated. The relevant thermoelectric properties are compared. Finally, we conclude that some strategies to effectively enhance the thermoelectric properties for PEDOT:PSS have been successfully developed, and there is still a long way to go for the actual applications. In particular, three tentative suggestions to the future investigations are proposed,i.e. in-depth investigation of the mechanism between microstructure and thermoelectric performances for the neat PEDOT:PSS, developing novel fabrication procedures with strong interfacial interaction like covalent-bonding and the relevant mechanism study, and exploiting of precise measurement techniques for the thermoelectric parameters of films, hydrogels and aerogels. Finally, the prospects of the future work are outlooked.关键词：Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate);Thermoelectric properties;Structure-performance relationship
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发布时间：2021-03-29 - 摘要：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.关键词：Rheology;Shear flow field;Shear rheology measurement
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发布时间：2021-03-05 - 摘要：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 prospects 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.关键词：Polymer characterization;Differential scanning calorimetry;Temperature-modulated DSC;Fast scanning chip-calorimetry
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发布时间：2021-03-05
Reviews
- 摘要：The power conversion efficiency of polymer solar cells (PSCs) is approaching commercial requirements, but its poor stability has become the next key challenge before the commercialization of PSCs. The high temperature working environment is what PSCs must endure in actual work, so it is necessary to improve the thermal stability of PSCs. Poly(3-hexylthiophene-2,5-diyl (P3HT):[6,6]-Phenyl-C61-butyric acid methyl ester (PC61BM)-based PSCs was used as a research model to investigate its degradation behavior at different annealing temperatures (50−110 °C). The results show that the PSCs exhibit an abnormal thermally induced stability enhancement behavior. During the high temperature aging process, the power conversion efficiency (PCE) of PSCs abruptly decay 20%−25% within the first 10 h, and then quickly recovered within 200 h, and finally remained stable for a long time (1000 h). Optical microscopy and laser beam induced current imaging characterizations prove that the top electrode covering can effectively inhibit the aggregation and crystallization of PC61BM in the active layer, so the abnormal aging behavior of the PSCs is not caused by the large amount of aggregation of PC61BM. Ultraviolet-visible absorption and external quantum efficiency characterizations prove that continuous high-temperature heating does not promote PC61BM dimerization, but facilitates the dissociation of PC61BM dimers. Based on all the above experimental results, it is speculated that the dimerization of PC61BM and the dissociation of its dimer at high temperature are the main reasons for the abnormal thermal stability enhancement of PSCs. This study also reveal that the newly prepared PSCs are actually in a metastable state, and a short-term thermal annealing of the device in the early stage is helpful to improve the stability of PSCs. This research work not only explains the thermally induced abnormal stability enhancement mechanism of fullerene-based PSCs, but also provides a new strategy to improve the stability of PSCs.关键词：Polymer solar cell;Thermal stability;Degradation;Metastable state;Fullerene
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发布时间：2021-03-05 - 摘要：Polyimide (PI) containing benzimidazole structure exhibits good heat resistance and dimensional stability due to the intermolecular hydrogen bonding, which is regarded as promising substrate material for OLED flexible display devices. However, the dissociation of hydrogen bonds at high temperatures results in PI film high thermal expansion coefficient in the temperature range above 300 °C, limiting the practicality of the PI film as the flexible display substrate material. In this study, the dianhydride containing alkynyl structure was introduced into the PI’s main chain, and chemically restricted sites were constructed by chemical crosslinking reactions to suppress the dissociation of hydrogen bonds at high temperatures, thereby improving the thermal performance of the PI film. The results show that, compared with linear polyimide, the hydrogen bonding content of PI at 400 °C is increased by nearly 50% after crosslinking. Correspondingly, the glass transition temperature of the chemically cross-linked PI film is as high as 452 °C, and the thermal expansion coefficient in the range of 40−400 °C is only 2.1×10−6/K. And the tensile strength of obtained PI film reaches 230.9 MPa. This PI film would be as potential substrate material for flexible display devices.关键词：Polyimide;Hydrogen bond;Chemical crosslinking;Dimensional stability
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发布时间：2021-03-05 - 摘要：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.关键词：Photosensitive polyimide;Curing process;Cross-linked film
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发布时间：2021-03-05 - 摘要：The precursor derived ceramics is an efficient and widely used method for preparing the SiBCN ceramics and their composites. This method demonstrates many advantages, such as low molding temperature as well as tunable product structure and composition. In this study, a liquid polyborosilazane precursor (PBSZ) was prepared by the coammonolysis reaction of dichlorosilane, dichloromethylvinylsilane and borazine derivative, which attained by the reaction between ethynyl magnesium chloride and B-trichloroborazine (TCB). After subsequent curing and pyrolysis of PBSZ, the SiBCN ceramic material was obtained. The structures of the PBSZ and the cured PBSZ were characterized by FTIR and 1H-NMR. Ceramicization process of PBSZ and its structure were investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and SEM. The results exhibited that PBSZ could be soluble in common organic solvents such as dichloromethane and chloroform, along with excellent fluidity and processability. The ceramic yield of the SiBCN ceramics derived from PBSZ was observed to exceed 80%. The pyrolysis products sintered below 1400 °C exhibited the amorphous microstructures. At 1500 °C, the derived ceramic materials turned out to contain α-Si3N4, β-Si3N4, h-BN and SiO2 crystals. The SEM analysis revealed that the surface of the pyrolysis products was smooth and dense. Moreover, the SiBCN ceramics exhibited excellent thermal stability and oxidation resistance.关键词：B-trichloroborazine;SiBCN ceramic precursor;SiBCN ceramics;Ceramization
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发布时间：2021-03-05 - 摘要：A series of microcellular thermoplastic polyurethane foams with different apparent densities were prepared by temperature-increasing foaming method with high-pressure CO 2 as blowing agent, and the relationship between the apparent density and mechanical properties was investigated. The structure of microcellular thermoplastic foam was characterized by scanning electron microscopy. The mechanical properties of the materials with different apparent densities were characterized by universal material testing machine and rotational rheometer. The results show that the apparent density of the microcellular thermoplastic polyurethane foam is mainly determined by the thickness ratio of the skin layer and the area occupation of cell. The smaller the ratio of the thickness of the skin layer and the higher the area occupation of cell, the smaller the foam density; the relationship between compression modulus E and apparent density ρ of the samples in the linear strain region is as follows: E∝ρ1.7, which is consistent with the basic conclusion that the relationship between modulus and density of foam materials is exponential; in the cyclic compression experiment, as the density of the foam material decreases, the residual strain decreases, and the hysteresis increase; in the rheological experiment, the modulus of the foamed material does not change significantly with the density, and the damping factor tanδ does not vary monotonically with the foam density. At the same time, the dependence of compression modulus E and hysteresis with foam density was also explained.关键词：Microcellular thermoplastic polyurethane foam;Skin;Apparent density;Mechanical properties;Rheology
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发布时间：2021-03-05 - 摘要：Bio-based nylon (PA56) is derived from natural products, which is expected to replace other synthetic nylon products. In order to prepare thermal conductive composites materials based on PA56, molecular dynamics simulation technology is used to explore the interface thermal resistance of graphene/PA56 composite materials. Firstly, the model and simulation parameters for simulated PA56 are testified by comparing physical properties, such as density, temperature of glass transition and thermal conductivity from simulation with those from experiment. There is a good accordance between simulation data and experimental data. And then, the simulated composites of graphene/PA56 is constructed. Various surface modification technologies onto graphene to depress interface thermal resistance between graphene and PA56 matrix are checked in detail. Typically, in cases surface grafted chains onto graphene those may form hydrogen bond with PA56 segments, are more effective to depress interface thermal resistance in the composites than other technologies. Experimentally surface grafting polymer chains onto graphene are expensive and inefficient, compared with that of chemical groups, though. To make a commercially viable surface modification technique, a diblock copolymer PA4-b-PA56 is theoretically designed as macromolecular interfacial modifiers. In the composites, the PA4 segments of diblock copolymer form hydrogen bonds with chemical groups onto modified graphene, and PA56 segments readily mix with matrix polymer chains. As a result, interface thermal resistance between graphene and PA56 matrix are found to be effectively depressed by such macromolecular interfacial modifiers. Such methodology opens a new routine to improve thermal transition among composites. Simulation exploration may help experimentally fabricate thermal conductive graphene/PA56 materials.关键词：Bio-based nylon;Graphene;Interface thermal resistance;Hydrogen bond
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发布时间：2021-03-05
Research Article
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