Self-healing behavior

Supramolecular polymers are linear chains of low molar mass monomers held together by reversible and highly directional non-covalent interactions. In suitable experimental conditions, they can display polymer-like rheological or mechanical properties, because of their macromolecular architecture. However, the fact that non-covalent interactions are involved means that the assembly can be reversibly broken. This reversibility brings additional features compared to usual polymers, which can potentially lead to new properties, such as improved processing, self-healing behavior or stimuli responsiveness. 

As commented in I rcface, the self-healing behavior of every self-healing liquid chemical, with the exception of liquid high explosives, such as nitroglycerin, of the true AC type, is ofthc TD type, so tltat a sclf-hcating liquid chemical of the TD type or self-heating liquid chemicals of the TD type are described hereafter simply as a liquid or liquids. 

The type of the self-healing behavior of a self-healing powdery chemical is closely related to the pattern of the thermogravimctry-diffcrcntial thermal analysis (TG-DTA) curve which the chemical affords. In other words, it is possible, in principle, to infer the self-healing behavior of a self-healing powdery chemical to be either of the TD type or of the quasi-AC type by glancing over the TG-DTA cuiwe of the chemical, so that it is also possible to infer the equation of the thermal explosion theory applied to calculate the of the chemical to be either the Semenov equation, i.e., Eq. (17) presented in Section 1.2, or the F-K equation, i.e., Eq. (29) presented in Section 1.3, or neither equation. 

It is obvious that the absence of the melting point is characteristic of the DTA curve of a powdery chemical of the TD type. That is, a powdery chemical of this type decomposes prior to melting. The self-heating behavior of a powdery chemical, such as 98 % O, a -azobis(isobutyronitrile) (AIBN), which decomposes explosively prior to any remarkable exothennic decomposition reaction, is also of the TD type, so that the F-K equation is applied to calculate its 1. When confined in the closed cell and subjected to the adiabatic selfheating test started from a in the range of 65 to 74 C, 2 cm of AIBN shows such a self-healing behavior, which is typical of liquid, or powdery, chemicals of the TD type, as exemplified in Fig. 15. 

Spider silks deserve additional commentary. Again, this example shows as that Nature never gives up to complexity, as if complexity were an intrinsic part of natural materials, and this is so even in these apparently simple materials that Nature has designed just to reach a given mechanical performance. Spider silks show a highly efficient self-healing behavior that is now under intense scrutiny due to its evident technological potential [25]. 

Recent studies have revealed a potential role for Fe coordination in bulk cross-linking and observed self-healing behavior of the byssal thread. Iron is now believed to form coordination complexes with catechols that are capable of yielding interesting bulk mechanical behavior such as time-dependent recovery after high strain. In a follow-up study, Holten-Andersen et demonstrated self-healing... 

Singha et al. reported DA cross-linked products [158] using furan-modified polymethacrylate (PFMA) as the polymeric precursor, which was prepared through atom transfer radical polymerization (ATRP) and free-radical polymerization (FRP). Furthermore, the self-healing behavior of a triblock copolymer (PFMA-co-MMA) prepared by ATRP was demonstrated by means of scanning electron microscopy (SEM). With the modification, an almost fully recovered surface from knife-cut samples has been observed [159]. Chen et al. also reported the DA polymer product of PFMA-BM possessing thermal reversibility, whereas the homopolymer was prepared from anionic polymerization [160]. 

S. Lee, M. Muller, R. Heeb, S. Ziircher, S. Tosatti, M. Heinrich, F. Amstad, S. Pechmann, N.D. Spencer. Self-Healing Behavior of a Polyelectrolyte-Based Lubricant Additive for Aqueous Lubrication of Oxide Materials. Tribology Letters (2006) Vol. 24(3), pp. 217-223. 

Self-healing behavior of a polyelectrolyte-based lubricant additive for aqueous lubrication of oxide materials... 

Lee S, Muller M, Heeb R, Ziircher S, Tosatti S, Heinrich M, Amstad F, Pechmann S, Spencer ND. Self-healing behavior of a polyelectrolyte-based lubricant additive for aqueous lubrication of oxide materials. Tribol. Lett. 2006 24(3) 217-223. 

Self-Healing Behavior of a Polyelectrolyte-Based Lubricant Additive for Aqueous Lubrication of Oxide Materials... 

A remarkable property of the interpolymer complex gels based on boronate-diol interactions is their self-healing behavior. Because the polymers are crosslinked with reversible boronate ester bonds, the network can form again once it is broken. As Kiser et al. showed, the network structure can... 

Enhancement in self healing ability has been necessary to actualize the self healing ceramics. For the purpose, SiC nanometer sizing was attempted as self healing is driven by the oxidation of SiC. In the present study, the self-healing behavior of alumina composites containing nanometer sized SiC particles whose particle sizes are less than 10 nm and 20-50 nm were investigated at several temperatures. 

Figure 3 SEM image of microstructure of AS18NPF SELF-HEALING BEHAVIOR...

The above-mentioned properties of metallopolymers are the basic requirements for the generation of self-healing behavior. As a consequence, it is possible to generate a reversible system and to introduce self-healing mechanisms, which is the principle of intrinsic self-healing systems [78-81]. 

In addition to the incorporation of the ligand function in the side chain, it is also possible to install the ligand in the main chain of the polymer. Yuan et al. showed that a self-healing behavior can be generated by polymers that feature ligands... 

In 2011, Rowan and Weder et al. described the self-healing properties of a linear metallopolymer. fii order to obtain self-healing behavior, the authors used UV light [44], For this purpose, poly (ethylene-co-butylene) was functionalized with two 2,6-fi/s(l -methylbenzimidazolyl)pyridine moieties at the termini and the subsequent addition of zinc di[Z>/s(trifluoromethylsulfonyl)imide] or lanthanum tri[6/s(trifluoromethylsulfonyl)imide] led to a linear metallopolymer. 

Recently, the basic concept of self-healing metallopolymer networks was improved. For this purpose, the Schubert group utilized cadmium(ll)-bis-terpyridine complexes [101]. A metallopolymer network based on these complexes was synthesized by the addition of cadmium acetate. The authors could show that these materials behave completely different due to a different coordination of the metal center. Presumably, the acetate moiety also coordinates to the cadmium, but this metal-ligand interaction is much weaker, which results in an improved self-healing behavior (Fig. 7). 

On the Figure 9 it appears that the cracks seem to be healed inside the matrix since they cannot be observed after 13h under air at 850 C. Moreover, the oxidation of TiB2 leads to the formation of Ti02 grains (reaction 5) which are covering the matrix surface (due to an increase of 1.64 in the molar volume ) and can act as an environmental barrier. Further characterizations on the self-healing behavior of this material are under progress. 

Ablation Mechanism and Self-Healing Behavior of the Composites... 

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