Healable materials could play an important role in reducing the environmental footprint of our modern technological society through extending the life cycles of consumer products and constructions. However, as most healing processes are carried out by heat alone, the ability to heal damage generally kills the parent material's thermal and mechanical properties. Here we present a dynamic covalent polymer network whose thermal healing ability can be switched ‘on' and ‘off' on demand by light, thereby providing local control over repair while retaining the advantageous macroscopic properties of static polymer networks. We employ a photoswitchable furan-based crosslinker, which reacts with short and mobile maleimide-substituted poly(lauryl methacrylate) chains forming strong covalent bonds while simultaneously allowing the reversible, spatiotemporally resolved control over thermally induced de- and re-crosslinking. We reason that our system can be adapted to more complex materials and has the potential to impact applications in responsive coatings, photolithography and microfabrication.

Advanced peptide-based nanomaterials composed of self-assembling peptides (SAPs) are of emerging interest in pharmaceutical and biomedical applications. The introduction of fluorine into peptides, in fact, offers unique opportunities to tune...

The curing mechanism of an epoxy film containing dicyandiamide (DICY) and an epoxy formulation based on diglycidyl ether of Bisphenol A (DGEBA) polymer was studied as a function of various temperature programs. The investigation was performed in situ, using a thin film of the epoxy mixture on a silicon wafer substrate in a heatable transmission tool of a FTIR spectrometer. Based on these model-curing experiments, a major curing mechanism was proposed, taking into account the appearance, the decrease, and the development of characteristic bands at various temperatures. The conclusions of the model curing were correlated to FTIR measurements on a real, 50-mm-thick glass fiber reinforced component composite part from a technical process. It could be shown that characteristic bands that develop at curing temperatures above 150 C appear especially in the center of the thick sample. The cure monitoring of epoxy resins and prepregs is a userorientated problem. The optimization and quality control of a curing program for complex, large-scale epoxy-composite structures with various mechanical loads, such as for wind turbines or aerospace/automotive parts, is important due to the cost of the process (in energy and time) and the durability of the material (mechanics). For practical purposes, it is common to monitor the relevant mechanical material or product characteristics, [1][2][3] instead to analyze the complex physical and chemical processes influencing the curing reaction of large-scale specimens. The analysis of these physicochemical parameters, such as crosslinking kinetics, viscosity, and micromechanics 4-8 is an area for intensive practicerelated research. The additional use of chemical analytics tools, such as infrared and Raman spectroscopy and high-pressure liquid chromatography, is also established as a way to understand the chemical reaction of the curing process. [9][10][11][12][13] In this article, we want to investigate the chemical reactions that take place during curing and correlate them to praxis. According to the literature, the temperature in the center of large-scale construction parts during the curing process can exceed the temperature of the mold. 1,3 This is caused by the heat flow of the exothermic reaction during the crosslinking reaction and the deteriorated temperature transport in the material. Therefore, we analyzed in situ the chemistry of resin during curing up to the start of decomposition. The results obtained were correlated to practical applications, namely, to a composite bar specimen cured in a large-scale compressing mold.To analyze the chemistry, we used an in situ heatable infrared tool and observed the curing process of a thin film in situ at various temperature profiles. In contrast to more common cure-monitoring tools, such as differential scanning calorimetry (DSC), rheology, and ultrasonic measurements, in the infrared spectroscopy, reactive bonds are measured, independent of their contribution to a material characteristic. This means that the infrared analysis ca...

No abstract

No abstract