The thermal self-healing properties of phenolic polyurethane derived from polyphenols with different substituent groups

Phenolic hydroxyl gave thermal self-healing ability to phenolic polyurethanes in our previous study. To explore, the feasibility of preparing self-healing polyurethanes through polyphenols with different substituents. Urushiol, propyl gallate, catechol, and tert-butylhydroquinone were chosen for preparation of four phenolic polyurethanes, and the different factors at the structures of these polyphenols worked together led the different properties and self-healing ability. The peak temperatures of these four polyurethanes were determined by DSC in the following order: PTHFTDI-Urushiol < PTHFTDI-Catechol < PTHFTDI-Propyl gallate < PTHFTDI-Tert-butylhydroquinone. Variable-temperature FT-IR spectra displayed that PTHFTDI-Propyl gallate with electron-withdrawing substituent exhibited the lowest decomposition and healing temperatures. Meanwhile, based on TGA analysis, lower decomposition temperature suggested lower thermostability; and PTHFTDI-Urushiol with electron-donating substituent exhibited the best thermostability. At the same temperature, the healing abilities of the three polyurethanes were ranked as follows: PTHFTDI-Catechol < PTHFTDI-Urushiol < PTHFTDI-Propyl gallate. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47039.     

Damage evolution in a self-healing air plasma sprayed thermal barrier coating containing self-shielding MoSi2 particles

A self-healing thermal barrier coating (TBC) system is manufactured by air plasma spraying (APS) and tested by thermal cycling. The ceramic topcoat in the self-healing APS TBC system consists of an yttria stabilised zirconia (YSZ) matrix and contains self-shielding aluminium containing MoSi₂ healing particles dispersed close to the topcoat/bond coat interface. After spraying the healing particles the material was annealed to promote the formation of an oxygen impermeable Al₂O₃ shell at the MoSi₂-TBC interfaces by selective oxidation of the aluminium fraction. The samples were subsequently thermally cycled between room temperature and 1100°C. The study focussed on the spontaneous formation of the Al₂O₃ shell as well as the subsequent damage evolution in the APS produced TBC during thermal cycling. Experimental evidence showing characteristic signs of crack healing in the topcoat is identified and analysed. The study shows that while the concept of the self-healing APS TBCs containing self-shielding MoSi₂ particles is promising, future study is needed to improve the protectiveness of the Al₂O₃ shells by further tailoring the aluminium content in the MoSi₂ and the particle shape to avoid the premature oxidation of the healing particles and maximise crack healing efficiency.     

Self-healing of TiSiN/Ag coatings induced by Ag

Ceramic coatings often suffer from the formation and expansion of microcracks, which leads to a failure of the protective function. In this work, we observed self-healing of the microcracks in the TiSiN/Ag multilayer coating upon heating. This behavior can be attributed to diffusion of the Ag atoms to the cracks in the multilayer coating, while similar cracks in the TiSiN monolayer coating remain unchanged after the same treatment. Furthermore, the TiSiN/Ag coating with healed cracks possesses similar electrochemical corrosion and biofouling properties to the as-deposited one, suggesting that TiSiN/Ag is a promising system in marine engineering applications. The mechanism of self-healing was explained by kinetic simulations based on ab initio molecular dynamics and the diffusion activation energies of Ag in irregular ceramic structures have been calculated. The here adopted theoretical method also provides a new pathway for exploring new coating systems with a potential self-healing function.     

Self-Healing Dynamic Polymeric Systems

The concept of self-healing has created a paradigm shift in the development of a new kind of responsive polymeric materials, which have traditionally been used in a passive role. Inspired by nature, the advancements made in this nascent field of research have given materials the ability of not only sensing damage but also responding and mending themselves in an appropriate manner. Self-healing in polymers can be autonomous, without the need for human intervention, or nonautonomous, requiring some form of external stimulus. The latter type involves the incorporation of dynamic bonds within the polymeric system, giving the ability to heal multiple times. This minireview discusses some of the prominent self-healing polymeric systems that harness different dynamic bond chemistries, with the aim of highlighting the potential of dynamic bonds to prepare such advanced materials.     

微生物与矿物建筑材料的相互作用(英文)

综合介绍了比利时根特大学Magnel实验室与其他合作单位关于微生物与建筑材料(混凝土和石材)之间相互作用的研究概况。第一个研究课题是生物硫酸腐蚀,主要研究混凝土下水道系统和储肥设施的侵蚀。整个过程可用纯化学或微生物侵蚀实验来模拟。利用化学硫酸实验来模拟侵蚀过程的缺点是忽视了混凝土本身的杀菌效果。微生物实验结果表明使用具有高度中和能力的材料可限制生物腐蚀的发生。因此,生物硫酸侵蚀模型中不但需要考虑耐久性(如孔隙率),也需要把混凝土碱性列为参数之一。第二个研究课题是细菌在胶结固化和混凝土自修复中的应用。细菌诱导产生的碳酸钙用于水泥基材料和石灰石的表面防护。研究表明:沉积在表面的生物碳酸钙可有效降低混凝土吸水率、碳化和氯离子侵蚀;还能提高混凝土抗冻融性能。多孔石灰石表面固化深度可达到30mm甚至更多,固结区的强度可增加300%。与此同时,微生物碳酸钙也被应用于混凝土裂缝自修复。细菌先被固载于硅藻土或微胶囊内,然后加入到混凝土中与其一起搅拌。结果显示:加有硅藻土固载的细菌的砂浆试块上0.15~0.17mm宽的裂缝可在40d内被细菌诱导产生的碳酸钙完全修复;而加有微胶囊固载的细菌的试块上1mm宽的裂缝可以在3周内自修复完毕。微生物在混凝土中的另一个应用是创造绿色生态混凝土墙壁。这种混凝土墙壁经过特殊设计获得特定的微观结构和生物兼容性,从而可充当生物生长的基体。为了适于生物生长,使用低pH值的磷酸镁水泥混凝土和碳化水泥混凝土,并对其他影响生物兼容性的因素如混凝土孔隙率、表面粗糙度等进行了优化研究。     

对混凝土裂缝自愈合的研究

阐述了混凝土裂缝产生的原因以及混凝土裂缝自愈合的机理,并对混凝土的自愈合技术进行了深入的研究,结合该领域存在的问题,对其在未来的发展进行了展望,以期为该问题的研究提供借鉴。     

An Optimal Strategy for the Constrained Cycle Cover Problem

A common telecommunications network design strategy, in order to protect it against failures, is to achieve a decomposition into a set of rings covering the network. We propose a hybrid algorithm for the corresponding Constrained Cycle Cover Problem which draws from constraint programming and graph algorithms. Optimal solutions are obtained efficiently on networks of realistic size.     

光传送Mesh网生存性的定量分析

生存性是光传送网络中亟待解决的问题，研究了光传送Mesh网的工作流量及所需的空闲容量的最佳分布问题，对问题进行了形式化描述，其目的是对给定的恢复需求使得后备容量最小，并根据后备容量的价值对不同的恢复策略进行比较，为实际网络的设计提供了一定的指导。     

DWDM网络生存性的研究

密集波分复用(DWDM)技术可以充分利用光纤的带宽资源，提供极大的传输容量，其生存性对于网络性能和服务至关重要。文中首先介绍了DWDM网络保护和自愈的基本技术，分析了不同拓扑结构的DWDM网络的生存性，最后阐述了多层自愈机制的协调问题。     

Feasibility study of a passive smart self-healing cementitious composite

The basic concept of a passive smart-healing cementitious composite has been demonstrated, in the laboratory, to be feasible. The basic elements of this smart material include the sensors and actuators in the form of controlled microcracks and hollow glass fibers carrying air-curing chemicals. Controlled microcracking is offered by a strain-hardening engineered cementitious composite developed previously. The mechanisms of sensing and actuation are revealed through in situ environmental scanning electron microscopy observations. The self-healing effectiveness is confirmed by measurement of the elastic modulus of the composite. The elastic modulus is found to regain its original value in a repeat loading subsequent to damage in a first load cycle.