Herstellung von Nanokomposit-Dünnschichten mit speziellen magnetischen Eigenschaften aus nanopartikulären Bausteinen

The combination of materials with different magnetic properties at the nanoscale can lead to phenomena such as exchange bias via coupling effects, which shows huge potential for applications, e.g., in storage media or magnetic sensors. Whilst such structures so far are obtained via complex processes of alternating deposition from the gas phase hampering their application, their preparation from nanoparticle dispersions would not only be simplified but also enable a broad variety of possible material combinations and structures. Thereby, the processing of hard magnetic nanoparticles is challenging but can be circumvented by the use of precursor materials with subsequent phase transformation.     

Biomimetic Design of Artificial Materials Inspired by Iridescent Nacre Structure and Its Growth Mechanism

Nacre, the iridescent material found in the innermost layer of seashells, having high strength and toughness was obtained from relatively weak constituents. The excellent mechanical performance of this biological material originates from its hierarchically ordered arrangement of well-tailored hard and soft building blocks. Incorporating these structures into composites is as alluring as conventional engineering materials often sacrifice strength to improve toughness. The unique mechanical properties originated from multiscale deformation regime involving solid-state self-organization process lead efficient energy dissipation which leads to high toughness, these multiscale biological assemblies inspire new synthesis route of complex materials. In this review, we study various mechanisms involved in toughening, methods used in mimicking nacre structure and various strategies for fabricating nacreous architecture which has gleaned new avenues for self-standing, strong, and advanced toughened material.     

The role of diisocyanate structure on microphase separation of solution polymerized polyureas

Three diisocyanates with different symmetry and planarity (2,6-TDI, 2,4-TDI and MDI) were used to synthesize polyureas with the same oligomeric polyetheramine having a molecular weight of ∼1000 g/mol. The influence of diisocyanate symmetry on the phase separated morphology, hydrogen bonding behavior, and molecular dynamics were investigated. Symmetric diisocyanate structures facilitated self-assembly of hard segments into ribbon-like domains, driven by strong bidentate hydrogen bonding. The hard domains for the 2,6-TDI polymer appear to be continuous in AFM images, while the persistence length of the hard domains in the 2,4-TDI and MDI polymers gradually decrease, and fewer hard domains are apparent with decreasing hard segment symmetry. The extent of hard/soft segment demixing, assessed from small-angle X-ray scattering, was very incomplete for all of the polyureas and is significantly influenced by hard segment structure. For the 2,4- and 2,6-TDI polyureas, two segmental relaxations were observed using dielectric relaxation spectroscopy; one arising from relatively unrestricted motion in the soft segment rich phase, and a slower process associated with segments in the soft phase constrained by their attachment to hard domains.     

一种纤维用新型聚乙二醇固-固相变储能材料

根据固-固相变材料的性质与结构特点,通过分子设计合成出了一种新型的芳香族四羟基化合物——4,4'-二苯基甲烷二异氰酸甘油酯(MTE),同时以4,4'-二苯基甲烷二异氰酸酯(MDI)-MTE为硬段,以聚乙二醇为相变单元和软段,通过原位聚合法制备出了一种聚乙二醇固-固相变储能材料(P-PCM)。利用红外光谱、核磁共振光谱、差示扫描量热法、动态热机械分析法研究了P-PCM的结构、相变行为及热稳定性,表明了P-PCM是一种新型的性能优异的相变材料。由于材料的刚性、可熔融和可溶解性,适合于纤维与织物的加工使用。     

Soft vesicles in the synthesis of hard materials

Vesicles of surfactants in aqueous solution have received considerable attention because of their use as simple model systems for biological membranes and their applications in various fields including colloids, pharmaceuticals, and materials. Because of their architecture, vesicles could prove useful as "soft" templates for the synthesis of "hard materials". The vesicle phase, however, has been challenging and difficult to work with in the construction of hard materials. In the solution-phase synthesis of various inorganic or macromolecular materials, templating methods provide a powerful strategy to control the size, morphology, and composition of the resulting micro- and nanostructures. In comparison with hard templates, soft templates are generally constructed using amphiphilic molecules, especially surfactants and amphiphilic polymers. These types of compounds offer advantages including the wide variety of available templates, simple fabrication processes under mild conditions, and easy removal of the templates with less damage to the final structures. Researchers have used many ordered molecular aggregates such as vesicles, micelles, liquid crystals, emulsion droplets, and lipid nanotubes as templates or structure-directing agents to control the synthesis or assembly hard micro- and nanomaterials composed from inorganic compounds or polymers. In addition to their range of sizes and morphologies, vesicles present unique structures that can simultaneously supply different microenvironments for the growth and assembly of hard materials: the inner chamber of vesicles, the outer surface of the vesicles, and the space between bilayers. Two main approaches for applying vesicles in the field of hard materials have been explored: (i) in situ synthesis of micro- or nanomaterials within a specific microenvironment by vesicle templating and (ii) the assembly or incorporation of guest materials during the formation of vesicles. This Account provides an in-depth look at the research concerning the association of soft vesicles with hard materials by our laboratory and others. We summarize three main principles of soft vesicle usage in the synthesis of hard materials and detailed procedures for vesicle templating and the characterization of the synthetic mechanisms. By use of these guiding principles, a variety of inorganic materials have been prepared, such as quantum dots, noble metal nanoparticles, mesoporous structures, and hollow capsules. Polymerization within the vesicle bilayers enhances vesicle stability, and this strategy has been developed to synthesize hollow polymer materials. Since 2004, our group has pursued a completely different strategy in the synthesis of micro- and nanomaterials using vesicles as reactive templates. In this method, the vesicles act not only as templates but also as reactive precursors. Because of the location of metal ions on the bilayer membranes, such reactions are restricted to the interface of the vesicle membrane and solution. Finally, using the perspective of soft matter chemistry, we stress some basic criteria for vesicle templating.     

Spider Silk Inspired Robust and Photoluminescent Soybean-Protein-Based Materials

Development of mechanical robust and functional biomass-based materials still remains challenging. Here, a design strategy inspired by spider silk structure is proposed to prepare strong, robust, and photoluminescent soybean protein isolate (SPI)-based materials, by integrating epoxy soybean oil (ESO) and SPI as soft phase matrices and graphene oxide quantum dots (GQDs) as hard phase. The results show that the soft–hard coordination network can form a close covalent/hydrogen bond network. The tensile strength, elongation at break, and toughness of the SPI/ESO/GQD film are 13.22 MPa, 209%, and 22.54 MJ m⁻³, respectively. In addition, SPI/ESO/GQD has strong photoluminescence intensity due to the ring-opening polymerization of amino structure with epoxy resin. The prepared SPI-based materials are promising candidates for optical coatings and provide new ideas for the intelligent research of other protein-based materials.     

木质素基介孔碳材料的制备及应用进展

木质素是自然界中唯一可提供再生性芳香基化合物的非石油类资源,酚羟基的可替代性、低成本及其高含碳量使其成为合成可持续介孔碳的优选前体。本文分别介绍了采用硬模板法、软模板法、双模板法、活化法、水热法以及溶胶-凝胶法制备木质素基介孔碳材料的最新研究进展。分析对比了采用不同方法制备的介孔碳材料所具有的孔道结构和形貌特点,并详细说明了其在吸附、催化、药物缓释和超级电容器等主要方面的应用。最后根据木质素基介孔碳材料在制备及应用过程中所面临的困境,提出发展一种简单、绿色、低成本的合成方法用以制备新型介孔结构的高性能复合型木质素基介孔碳材料将成为今后主要的研究方向。     

Thermoplastic urethane elastomers. III. Effects of variations in isocyanate structure

The dynamic mechanical properties of thermoplastic urethane elastomers have been compared for materials based on different diisocyanate structures, either 4,4′-diphenylmethane diisocyanate (MDI) or an isomeric ratio of tolylene diisocyanate (TDI). Two comparable series of polymers were prepared with a polycaprolactone diol as the soft segment and varying concentrations of hard segments based on the respective diisocyanates and 1,4-butanediol. Over the composition range studied, the polymer glass transition temperatures increased for the TDI-based polyurethanes, but remained relatively constant for the series containing MDI. Differences in the degree of macroscopic order within the hard segments, due to variations in the symmetry of the diisocyanate structures, are suggested as an explanation of these dynamic mechanical properties.     

Thermoplastic polyurethane elastomers based on polycarbonate diols with different soft segment molecular weight and chemical structure: Mechanical and thermal properties

A series of thermoplastic polyurethane elastomers based on polycarbonate diol, 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol was synthesized in bulk by two‐step polymerization varying polycarbonate diol soft segment molecular weight and chemical structure, and also hard segment content, and their effects on the thermal and mechanical properties were investigated. Dynamic mechanical analysis termogravimetric analysis, differential scanning calorimetry, Fourier transform infrared‐attenuated total reflection spectroscopy and mechanical tests were employed to characterize the polyurethanes. Thermal and mechanical properties are discussed from the viewpoint of microphase domain separation of hard and soft segments. On one hand, an increase in soft segment length, and on the other hand an increase in the hard segment content, i.e., hard segment molecular weight, was accompanied by an increase in the microphase separation degree, hard domain order and crystallinity, and stiffness. In phase separated systems more developed reinforcing hard domain structure is observed. These hard segment structures, in addition to the elastic nature of soft segment, provide enough physical crosslink sites to have elastomeric behavior. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

Phase separation in segmented polyurethanes

Phase separation in a segmented polyurethane has been studied by differential scanning calorimetry. The glass transition temperature of the soft phase decreases logarithmically with time to a limiting value at each annealing temperature. The magnitude of the decrease is larger at low annealing temperatures, but the normalized rate of logarithmic decrease is smaller. At high annealing temperatures, long sequences of hard segments are excluded from the soft phase in which short segments are still soluble. At low temperatures, even short hard segments separate from the soft phase. The exclusion of the hard segments from the soft phase is a relatively fast process, but the development of order in hard domains takes longer time to reach steady state.     

Development of shape memory polyurethane based on polyethylene glycol and liquefied 4,4′‐diphenylmethane diisocyanate using a bulk method for biomedical applications

In this study, a series of shape memory polyurethanes (SMPUs) were synthesized successfully by the bulk polymerization method from liquefied 4,4′‐diphenylmethane diisocyanate (L‐MDI), 1,4‐butanediol (BDO) and polyethylene glycol (PEG). The influence of the hard segment content (HSC) on the structure, morphology, properties and biocompatibility of PEG based SMPUs (PEGSMPUs) was carefully investigated. The results show that a microphase separation structure composed of a semicrystalline soft phase and an amorphous hard phase is formed in the PEG6000/L‐MDI/BDO system. Crystallization of the PEG soft segment is influenced by the hard segments. The PEG semicrystalline soft phase serves as a reversible phase while the L‐MDI?BDO hard segment acts as physical netpoints. Finally, a cyclic tensile test shows that all PEGSMPUs have good shape recovery (e.g. above 80%), whereas good shape fixity can only be achieved when the HSC is less than 35 wt%. The Cell Counting Kit 8 assay also demonstrates that only PEGSMPUs containing less than 40 wt% HSC have low cytotoxicity. It is thus concluded that PEGSMPUs bearing both good shape memory effects and good biocompatibility can be used as shape memory materials for biomedical applications when the HSC is less than 35 wt%. © 2014 Society of Chemical Industry     

磁场作用下冷冻铸造法制备仿生材料研究进展

随着科技的迅速发展,对材料的性能提出了更高的要求,迫切需要开发新型轻质高性能结构材料,即低密度、高刚度、高强度和高韧性等特点集于一身。生物材料经过数亿年的进化,形成了与环境和功能需求相适应的精细复杂结构,如贝壳珍珠层的“砖-泥”结构和螃蟹角质层的螺旋结构,它们均表现出非凡的机械性能和独特的功能特性,这启发了人们对于高性能材料的设计和构筑。目前发展的冷冻铸造法(即冰模板法)是制备仿生材料的一种有效方法,通常在温度梯度作用下定向凝固水基陶瓷浆料,经冷冻干燥后可获得具有精细结构的多孔陶瓷材料,随后对该多孔陶瓷填充软相-树脂后可获得仿珍珠贝结构陶瓷-树脂复合材料。为了进一步控制材料微观结构,研究人员对冷冻铸造过程施加磁场作用,最终发现材料的结构和性能均发生了明显变化。本文介绍了冷冻铸造法在控制材料微观结构以及制备仿生材料方面取得的一些进展,综述了施加磁场作用对冷冻铸造的影响,总结了施加磁场辅助的冰模板材料微观结构和机械性能变化规律。     

Enhancing polyurethane properties via soft segment crystallization

Semi-crystalline polyester diols with relatively high melting points and enthalpies of crystallization are shown to form nearly co-continuous lamellar structures in thermoplastic polyurethanes using polyether soft segments. This high aspect ratio crystalline structure results in materials with exceptional tensile and elastic properties compared to materials made with conventional semi-crystalline soft segments such as polycaprolactone or polybutylene adipate. Additions of semi-crystalline soft segment to foam formulations also result in increased hardness measured by standard foam hardness tests. Halpin-Tsai and percolation model analyses of the results suggest that the crystalline regions exert a global influence on the elastomer structure.     

不同软硬段含量的聚醚酯纤维结构与性能的关系

为了说明聚醚酯纤维的形态结构与性能的对应关系,选择不同软硬段含量的聚醚酯切片进行熔融纺丝试验。结果发现:随着硬段含量的增加,纤维的断裂强度增大,但回弹性降低;当硬段质量分数为65%时,纤维的断裂强度为1.12 cN/dtex,而回弹性降至50%左右。通过广角X射线散射、小角X射线散射以及双折射、声速取向等试验进一步分析了不同软硬段含量的聚醚酯纤维的形态结构变化,发现在硬段含量高的聚醚酯纤维内部有利于形成较高的取向结构,有助于纤维强度的提升;然而,此时纤维内形成较小尺寸的结晶结构分散于无定形区内,相分离程度低,致使其回弹性降低。     

Small angle x-ray studies of siloxane-urea segmented copolymers

Novel segmented copolymers were synthesized using aminopropyl terminated linear poly(dimethylsiloxane) oligomers as the soft component and various diisocyanates as the hard segments. As a result of the large differences in the cohesive energy density (solubility parameter) between the two components, phase separation occurs to form a microdomain structure at relatively low oligomer molecular weights. Since chain extenders were not employed during the synthesis, the “hard” segments are strictly related to the length of the diisocyanate moiety utilized in the reaction, In this paper we utilize these copolymers as reasonable models for investigating the various methods available for determining the interfacial layer thickness between the hard and soft phase. Specifically, in these systems there is no hard segment length distribution as is the usual case for segmented urethanes. Utilizing Porod's law, and appropriate analysis, both positive and negative deviations were found in the systematic series of copolymers. The degree of positive and negative character was found to be dependent upon copolymer composition. Negative deviations were accounted for in terms of a finite interfacial thickness, which turned out to be relatively small as anticipated, while the positive deviations were assigned to isolated hard segments that reside within the soft segment matrix, i.e., concentration fluctuations. In calculating the interfacial thickness, several methods were applied and in general, close agreement was obtained. Finally, correlation function analysis in conjunction with determination of the coherent Porod lengths, etc. were determined and discussed accordingly. Cautionary comments are also provided for researchers who apply less complete small angle x-ray scattering (SAXS) analysis to related block or segmented copolymers with regard to phase separation behavior.     

介孔碳微球的合成及其应用研究进展

目前,介孔碳微球的合成主要有硬模板和软模板两种方法。硬模板是将碳前驱体通过溶剂挥发填充到已合成的球形介孔材料(硬模板)中,然后热处理掉硬模板得到介孔碳微球;软模板则是以三嵌段共聚物F127做为模板剂,酚醛树脂作为碳源在水热条件下制备出介孔碳微球。介孔碳微球在超级电容、锂离子电池、气体储存、生物医药等领域获得广泛应用,然而在摩擦润滑领域的研究却未见报道。结合本课题组的前期研究提出了其在摩擦领域的研究思路并展望了其应用前景。     

Pyrolyzing soft template-containing poly(ionic liquid) into hierarchical N-doped porous carbon for electroreduction of carbon dioxide

Heteroatom-doped carbon materials have demonstrated great potential in the electrochemical reduction reaction of CO₂ (CO₂RR) due to their versatile structure and function. However, rational structure control remains one challenge. In this work, we reported a unique carbon precursor of soft template-containing porous poly(ionic liquid) (PIL) that was directly synthesized via free-radical self-polymerization of ionic liquid monomer in a soft template route. Variation of the carbonization temperature in a direct pyrolysis process without any additive yielded a series of carbon materials with facile adjustable textural properties and N species. Significantly, the integration of soft-template in the PIL precursor led to the formation of hierarchical porous carbon material with a higher surface area and larger pore size than that from the template-free precursor. In CO₂RR to CO, the champion catalyst gave a Faraday efficiency of 83.0% and a current density of 1.79 mA·cm^-2 at -0.9 V vs. reversible hydrogen electrode (vs. RHE). The abundant graphite N species and hierarchical pore structure, especially the unique hierarchical small-/ultra-micropores were revealed to enable better CO₂RR performance.     

Applicability of image correlation techniques to characterise asymmetric refractory creep during bending tests

The design of fibre reinforced refractory castable structures for high temperature applications requires the characterisation of the material creep behaviour. As many other heterogeneous ceramics, these materials creep faster under tensile stresses than under compressive ones because of the motion of hard particles in a soft matrix. Bending tests have been performed to characterise the creep behaviour of the considered material, and 3D digital image correlation is used to obtain strain fields after interrupted tests. The position of the neutral axis, defined here from the residual inelastic strain field, allows to highlight the asymmetry of creep and to evaluate the asymmetry ratio.     

模板法制备介孔TiO2的研究进展

介绍了采用软模板法和硬模板法制备介孔TiO 2的方法及其优缺点。软模板法和硬模板法制备介孔TiO 2的原理都是先将钛前驱体与模板进行组装,再通过焙烧等方式去除模板得到介孔结构。二者之间的区别在于所使用的模板不同,软模板容易得到,种类较多且方法简单,但不易控制介孔的结构;硬模板虽然种类较少,但胜在可以控制介孔的结构和性能。     

The effect of microstructure on the rate-dependent stress-strain behavior of poly(urethane urea) elastomers

Segmented poly(urethane urea) materials (PUUs) exhibit versatile mechanical properties and have drawn great interest due to their potential for protection against projectile impacts and blast loadings. To optimize the performance of PUUs for various high rate applications, specific features of their mechanical behavior have to be suitably tailored by altering the microstructure. Hence the micromechanisms governing the mechanical behavior must be identified, understood and leveraged. In this study, the effects of varying microstructure on the rate-dependent mechanical behavior were examined for select PUU materials. As expected, increasing the hard segment content increased the stiffness and the flow stress levels. Interestingly, it was observed that promoting phase mixing among the hard and soft segment domains of the PUU material greatly enhanced its rate-dependent stiffening and strain hardening behavior. These insights can help design PUUs for articles that manifest improved protective abilities under impact, while maintaining their flexibility during normal use. The potential applications for such materials are extensive, including face masks and goggles, which require excellent folding/un-folding capabilities, while also providing superior impact resistance.