最新刊期
卷 55 ， 期 2 ， 2024
- 摘要：DNA is the most important molecule for forming the basis of life. Whether and how DNA conducts electricity is highly related to the understanding and revelation of the transmission of life signals and life phenomena, as well as the development of programmable DNA molecular electronics. Thus, this topic has attracted tremendous attention worldwidely. However, DNA is a complex system that its conductivity property is still unclear and controversial. In this review, we briefly summarize the research history of DNA conductivity, analyze the main reasons for the controversy on DNA conductivity. The main problems existing in the study of DNA conductivity are mainly attributed to the diversity of measurement methods and the complexity of the DNA molecule. Finally, we propose the future development direction of DNA conductivity research. DNA conductivity has huge application potential in the fields of life signal transmission, biosensors, molecular electronics, etc. The research on DNA conductivity will also provide new ideas for the integration of biological science and electronics.关键词：DNA;Conductivity;Structure-property relationship;electric transport mechanism
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发布时间：2024-01-19
Review
- 摘要：Directed self-assembly of block copolymers has arouse tremendous interest from academy and industry as a bottom-up patterning process to fabricate versatile nanostructures. However, the underlying principles between molecular parameters and defectivities in directed self-assembly are still unambiguous due to the limitations of traditional polydisperse polymer models. Discrete polymer with defined molecular structure and uniform chain length are ideal candidates to reveal the fundamental principles. In this study, based on the modular synthesis strategy, discrete fluorine-containing polyester block copolymers (oLAn-FPOSS) with high χ-low N were firstly prepared by iterative exponential growth in combination with the thiol-ene click reaction. Owing to the discrete feature, the influence of polydisperse molecular parameters including composition, molecular weight and distribution on self-assembly behaviors can be completely excluded. Consequently, the impacts of molecular structures on the evolution of phase segregation can be quantitatively revealed. Due to the strong segregation strength, hexagonally packed cylindrical nanostructures (HEX) less than 10 nm can be formed in bulk and the phase stability increases with the chain length of oLA block. In thin-film self-assembly, parallelly oriented cylindrical nanopatterns on Si substrate were clearly identified after brief annealing under vacuum. In addition, through comparative studies of thin-film self-assembly behaviors of discrete block copolymers with different chain lengths, the nanopattern defectivity decreased significantly with the increase of oLA block chain length, which initially revealed the dependence of defect formation on block copolymer chain length in thin-film self-assembly.关键词：Discrete polymer;Directed self-assembly;Fluorine-containing block copolymer;Bulk and thin film self-assembly;Lithography
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发布时间：2024-01-19 - 摘要：The polymerization of 2-(4-methylphenyl)-1,3-butadiene (2-MPBD) is performed using [C13H8CH2CH2(NCHCCHN)C6H2Me3-2,4,6]Lu(CH2SiMe3)2 (1), Ph2P(=NDip)(NDip)Lu(CH2Si-Me3)2(THF) (Dip=C6H3-2,6-iPr2; 2), Ph2P(=NDip)(NC6H3-2-Et)Lu(CH2SiMe3)2(THF) (3) and Ph2P(=NDip)(NC6H3-2-Et)Sc(CH2SiMe3)2(THF) (4). The microstructures and thermal properties of resultant polymers are characterized by nuclear magnetic resonance spectroscopy (1H-NMR, 13C-NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). Complex 1, activated by [Ph3C][B(C6F5)4] and AliBu3, shows low catalytic activity and 3,4-selectivity (65.2%) for 2-MPBD polymerization. Under the same conditions, complex 2 is nearly inert. In contrast, complexes 3 and 4 demonstrate high 3,4-selectivity (98.1% and >99%, respectively) and enable 100% conversion of 200 equivalents of 2-MPBD into polymers at 20 ℃ with 2 min. The resultant molecular weights increase with monomer-to-catalyst ratios varying from 200:1 to 600:1 with narrow molecular weight distributions of 1.12-1.25. Furthermore, complex 4 also shows high catalytic activity and high 3,4-selectivity for the polymerizations of 2-phenyl-1,3-butadiene, 2-(3-methylphenyl)-1,3-butadiene, 2-(4-pentylphenyl)-1,3-butadiene, 2-(4-fluorophenyl)-1,3-butadiene and 2-(4-chlorophenyl)-1,3-butadiene. The resultant 3,4-poly(2-aryl-1,3-butadiene)s are readily transformed into hydroxyl functionalized polymers by the treatment of BH3 and H2O2.关键词：Rare-earth metal catalyst;Functional polyolefin;3;4-Selectivity;Conjugated diene;Reactive polyolefin intermediate
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发布时间：2024-01-19 - 摘要：We used three different structures of disilazane, hexamethyldisilazane (MMN), tetramethyldivinyldisilazane (MMNVi) and tetramethyldisilazane (MMNH), as a source of amine, which then reacted with chlorosilanes and boron trichloride, to produce polyborosilazanes with different end-capped structures. Among the reactants, liquid state products were acquired when using MMN and MMNVi as the amine source. While gelatine products were acquired when using MMNH as the amine source, due to the excess crosslink of the active group during synthesis. We then used nuclear magnetic resonance spectrometer and infrared spectrometer to characterize the liquid precursor polymer and its pyrolysis products. The results showed that the liquid polyborosilazane backbone made by one pot method had more branches and cyclic structures. As the vinyl group in the end-capped structure increases, the curing temperature of the precursor dropped and the activation energy of the curing reaction lowered. When compared to the polyborosilazane which is made by using MMN and the capping agent, the ceramic production rate increased by 14.9% and 8.1% when MMNVi made precursor curation occurred. Furthermore, SiBCN ceramic, made by pyrolysis of the synthetic precursor polymers, has a crystallization temperature higher than 1700 ℃. This conclusion is reached by adjusting the element composition through changing the amine source type and ratio.关键词：Precursor-derived;SiBCN ceramic;Polyborosilazane;"One-pot" synthesis
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发布时间：2024-01-19 - 摘要：Poly(γ-benzyl-L-glutamate) (PBLG) with propargyl terminal group and porphyrin derivatives containing single azide group (TFPP-N3) were used as reactants to synthesize porphyrin-based polypeptide (TFPP-PBLG) using a click reaction. The molecular structures of the polymers, including molecular weight, polydispersity index, and composition were characterized by nuclear magnetic resonance spectroscopy (1H-NMR), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectrophotometer (UV-Vis), and gel permeation chromatography (GPC). The critical water content (CWC) for the aggregation of the TFPP-PBLG polymers was determined by turbidity measurement (OD). By a selective precipitation method with water as the selective solvent, bowl-like aggregates with obvious pits were obtained. The solution self-assembly behavior was studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), dynamic laser light scattering (DLS) and small-angle X-ray scattering (SAXS). The results show that the TFPP-PBLG polymers can self-assemble into bowl-like aggregations when the PBLG chain is relatively short. Upon the addition of water, solubility of the solvent for polymers decreases, and the polymers aggregate into micelles. The π-π stacking effect contributed by porphyrin derivatives results in a relatively stable structure of the micelles. During the dialysis process, the solvent within the micelle diffuses outward while water is difficult into the micelles, causing the micelle to collapse and form a pit structure. As the solvent further diffuses, the pit becomes larger, ultimately leading to a bowl-like aggregate structure. Increasing the length of the PBLG makes the initial micelles more stable, which inhibits the collapse of the micelles under the dialysis process, as a result, ellipsoid micelles are maintained. The stability of the initial formed micelle is crucial in determining whether it undergoes depression during the subsequent dialysis process, ultimately resulting in the formation of nanobowls.关键词：Polypeptides;Porphyrin;Click reaction;Self-assembly;Nanobowls
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发布时间：2024-01-19 - 摘要：This study proposes utilizing thermosensitive surfactants, referred to as "environmentally responsive surfactants," as emulsifiers for addressing the complexity of demulsification and separation processes after emulsion polymerization reactions. A series of polyethylene glycol-poly(N-isopropylacrylamide) (PEG-b-PNIPAM) block copolymers with various degrees of polymerization were synthesized via atom transfer radical polymerization (ATRP). The PNIPAM segments within the copolymers exhibit thermosensitive behavior, possessing a lower critical solution temperature (LCST) at 32 ℃, enabling the control of hydrogen bond formation and rupture with water molecules based on temperature variations. Consequently, the PEG-b-PNIPAM block copolymers display hydrophilic properties at room temperature and amphiphilic properties in the range from 35 ℃ to 80 ℃. Surface tension measurements at different concentrations confirmed the low critical micelle concentration (CMC) of the PEG-PNIPAM block copolymers, with a minimum value as low as 9.10×10-3 g/L. Evaluations of particle size distribution and emulsification performance validated its applicability as an emulsifier in emulsion polymerization within the aforementioned temperature range. Microscopic observations of latex particles corroborated the precise occurrence of emulsion polymerization, displaying a relatively uniform particle size distribution in the resulting polymer. Upon completion of the emulsion polymerization reaction, the need for additional agents such as demulsifiers or physical methods like mechanical stirring was obviated. Merely lowering the reaction system to room temperature facilitated demulsification, yielding the desired polymer products. Further, rapid demulsification could be achieved by cooling the reaction system at lower temperatures (3‒8 ℃). Utilizing PEG-b-PNIPAM block copolymers as surfactants allowed the temperature-controlled emulsification and demulsification processes, significantly streamlining the emulsion polymerization process, reducing costs, and enabling environmentally friendly production practices.关键词：Thermosensitive surfactant;Emulsion polymerization;Block copolymer;Self-demulsification
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发布时间：2024-01-19 - 摘要：Hair dyeing has become an indispensable demand and fashion choice in people's daily lives. The issues of allergy, carcinogenicity, and gene mutation caused by the commonly used chemical hair dye, which mostly comprises p-phenylenediamine and other substances, are becoming noticeable. As a result, there is an urgent need for innovative materials to replace aniline in commercial hair dye. A biomimetic fabrication of polydopamine (PDA) inspired by natural melanin has been reported to have excellent hair dyeing effects. A strong alkaline oxidative environment or metal ion catalysis are usually indispensable for dopamine polymerization. However, excessive alkalinity will make the hair rough and affect its quality, and metal ions may be poisonous. As a result, developing a new type of mild, efficient, safe, and non-toxic synthetic melanin hair dye is an urgent concern. The more reactive melanin monomer 5,6-dihydroxyindole (DHI) may just conduct rapid polymerization by air oxidation, in contrast to DA, which requires demanding oxidation conditions to initiate polymerization. Herein, this work reported a hair dye material that polymerized DHI in situ on the surface and inside of hair under mild conditions. The L value of dyed hair is 30, and L=20 after washing 30 times. The results of the synthetic melanin hair dye to adhere uniformly to the hair surface have been demonstrated by electron microscopy, and some monomers and oligomers will also reach the cortical layer of the hair to polymerize. The poly-DHI (PDHI) structure can engage in a Michael addition reaction with the disulfide bond in the hair to form a covalent coupling due to its high reducibility and highly reactive double bond. The findings of skin sensitization tests demonstrate that using DHI polymerization to dye hair won't affect human skin or health, even at the greatest concentration permitted. Finally, it can be obtained an efficient, durable, and safe melanin hair dye, which provides an innovative design strategy and a dependable tool platform for the development of a new generation of hair dyes.关键词：Synthetic melanin;Polydioxindole;Hair dye;Bio-inspired material
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发布时间：2024-01-19 - 摘要：On the basis of electrodeposition, a new method has been developed to in situ synthesize zinc sulfide (ZnS) quantum dots (QDs) and directly prepare ZnS QDs/alginate composite films on electrodes. The method shows a range of benefits, such as the good controllability, the mild conditions, and the convenient and eco-friendly process. After the electrodeposition, a smooth and homogeneous ZnS QDs/zinc alginate composite film has been generated on the surface of electrode, which exhibits clear blue fluorescence under excitation of 302 nm UV light. Transmission electron microscopy observation reveals that there are relatively uniform sized nanoparticles in the ZnS QDs/zinc alginate composite film, and their average particle size is 3.0 nm. The UV-Vis absorption spectrum of the ZnS QDs/zinc alginate composite film exhibits absorption peak at 280 nm, which is attributed to the typical absorption peak of ZnS QDs. The photoluminescence spectrum of the ZnS QDs/zinc alginate composite film shows a clear emission peak at 420 nm, which agrees with the emission peak of ZnS QDs. The ZnS QDs/zinc alginate composite films having specific shapes and fluorescence patterns can be directly fabricated by utilizing the spatial selectivity of the electrodeposition and the fluorescence property of ZnS QDs. Noteworthily, the ZnS QDs/zinc alginate composite film shows the ability for both fluorescence detection and electrochemical detection. Therefore, it can be expected that the ZnS QDs/alginate composite film prepared by electrodeposition is promising for applications in the dual-mode detection and novel dual-mode detectors and sensors.关键词：Electrodeposition;ZnS quantum dots;Alginate;Electrochemical detection;Fluorescence detection
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发布时间：2024-01-19 - 摘要：In recent years, the thermal rearrangement (TR) membrane materials derived from hydroxyl-containing polyimides (HPI) as precursors have received extensive attention in the field of gas separation. In this study, the dihydroxy compound 4,4'-(4,5-diphenyl-(4-hydroxyphenyl))imidazole (PMOPPP) containing rigid and bulky tetraarylmidazole structure was first synthesized, and then reacted with 5-fluoro-2-nitrophenol to produce a dinitro compound 4,4'-(4,5-diphenyl-(3-hydroxy-4-nitrophenoxy)phenyl)imidazole (PMNPPP). After reduction treatment, a new kind of diamine monomer 4,4'-(4,5-diphenyl-(3-hydroxy-4-aminophenoxy)phenyl)imidazole (PMAPPP) was obtained. Then, the diamine PMAPPP was separately polymerized with five kinds of dianhydride monomers, followed by thermal imidization treatment to obtain HPI membranes. Subsequently, these membranes were further thermally treated at 450 ℃ for 1 h to obtain the corresponding TR membranes, and the structure and performance of these membrane materials were characterized. The testing results showed that the introduction of rigid and large volume tetraarylimidazole structure resulted in excellent thermal and mechanical properties of five HPI membranes, and the glass transition temperatures (Tg) were in the range of 263‒361 ℃ and the tensile strength ranged from 98.4 MPa to 118.3 MPa. Compared to HPI membrane materials, the gas separation performances of TR membranes were significantly improved. Among them, the TR(PMAPPP-6FDA) exhibited the highest gas permeabilities, namely H2 (269.31 Barrer), CO2 (284.25 Barrer), O2 (62.75 Barrer) and N2 (10.67 Barrer). Moreover, the ideal selectivities of CO2/N2, O2/N2 and H2/N2 were 25.24, 5.88 and 26.64, respectively, and the O2/N2 separation performance was beyond the 2008 Robeson upper bound.关键词：Tetraarylimidazole structure;Polyimide;Thermal rearrangement;Gas separation membranes
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发布时间：2024-01-19 - 摘要：The molecular dynamics simulation method based on the reactive force field (ReaxFF) was applied to investigate the basic process of diffusion of water molecules at the friction interface into ultra-high molecular weight polyethylene (UHMWPE) substrate. The molecular simulation results show that water molecules are stably adsorbed on the surface of the Fe plate during the friction process, and the internal friction between the Fe slab/water molecules and the UHMWPE substrate drives the shear and deformation process of polyethylene chains. Moreover, in the convex model with nano-scale convex ridges, the plowing effect on the UHMWPE becomes more obvious, which significantly increases the internal frictional force. However, if increasing the friction velocity, the atomic temperature at the frictional interface increases significantly. Under water-lubricating conditions, interfacial water molecules gradually diffuse into the UHMWPE substrate, which in turn increases the average atomic distance between adjacent polyethylene chains. As a result, interaction strength between polyethylene chains decreased. In addition, the rupture of the hydrogen-oxygen bonds in water molecules occurs during the frictional process, which also results in charge transfer at the frictional interface. Meanwhile, the water oxygen atoms after water dissociation and surface Fe atoms formed Fe－O compounds, which have a similar crystal structure to Fe2O3. The diffusion of water molecules into the UHMWPE substrate also causes rapid changes in the atomic charges of surrounding polyethylene chains, resulting in uneven distribution of atomic charges on the surface of UHMWPE.关键词：Reactive Force Field molecular dynamics simulation;Ultra-high molecular weight polyethylene;Water diffusion;Bond breakage;Charge transfer
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发布时间：2024-01-19
Research Article
- 摘要：The study of conformational changes in polymer chains, their assembly behavior, and the mechanisms behind these phenomena are fundamental problems in polymer science. These factors not only play a crucial role in determining the synthesis, properties and applications of polymer materials, but also have far-reaching implications for the study of biomolecular interactions and biochemical reaction systems. While substantial progress has been made in theoretical and computational methods, observing the dynamic behavior of single polymer chains and their assemblies in a solution state remains as a significant challenge. Liquid-phase transmission electron microscopy (LP-TEM) offers an unprecedented combination of atomic-level spatial resolution and millisecond temporal resolution. This innovative technique provides fresh opportunities to investigate the hidden dynamics of molecules that have traditionally been obscured by ensemble measurements. Electron microscopy has been widely used to analyze the morphology, crystalline structure, mechanical properties, and assembly structures of dry-state polymers. More recently, it has facilitated the study of the dynamic behavior of polymers in solution. The feasibility of LP-TEM experiments is largely owed to advancements in nanotechnologies, enabling the sealing of liquid samples within a chamber to prevent exposure to a vacuum environment. With a good understanding of electron beam-sample interactions and interface-sample interaction, real time imaging of individual macromolecules and their assembly pathways in solution have been successfully achieved despite their fragility. In this review, we first introduce the development of LP-TEM and its experimental setup, then summarize the progresses of LP-TEM experiments on the single chain dynamics of polymers, transient processes of macromolecular interactions, assembly pathways, and phase separations; with an emphasis on the experimental challenges and the corresponding methodological advancements that enabled these experiments. We also discuss the new questions triggered by observations from these experiments and the future directions including the challenges and possible technical assistance, as well as the new research opportunities that this goal will bring.关键词：Liquid phase electron microscopy;Polymer dynamics;Single-molecule imaging;Image processing
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发布时间：2024-01-19
Review (Special Topic: Techniques of Polymer Characterization)
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