Self-Healing Agents

On many occasions, cracks occur in polymer materials used in a wide variety of materials, including those used in transportation (automobiles, airplanes, spacecraft), sporting goods (tennis rackets, helmets, skis), medical devices (pacemakers. 

UF microcapsules containing DCPD have been prepared by in-situ polymerization in an oil-in-water emulsion [66]. Different experimental parameters such as agitation speed, temperature and pH have been studied in order to obtain microcapsules with a long shelf-life - that is, microcapsules which are impervious to leakage and diffusion of the encapsulated (liquid) heahng agent for a considerable time. 

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Lee, J.K. Liu, X., Yoon, S.H. Characterization of diene monomers as self-healing agent for polymer composite and its microcapsules. In Conference Proceedings, Society of Plastics Engineers, Annual Technical Conference 2005, ANTEC 2005, vol. 6, pp. 264-268. 

Polyurea - material, catalyst, self-healing agent. 

Functional material Electronic ink Carbonless paper Self-healing agent... 

Metal triflates in polymers were also reported as self-healing agents affording fiber-reinforced polymer composite materials. The Lewis acid catalyst in these materials is protected by polymer [131]. 

Lv L-P, Zhao Y, Vilbrandt N, Gallei M, Vimalanandan A, Rohwerder M, Landfester K, Crespy D (2013) Redox responsive release of hydrophobic self-healing agents from polyaniline capsules. J Am Chem Soc 135 14198-14205... 

Figure 7 Oxidation behaviors of the candidates for the advanced self-healing agents the crack above 577 °C within 10 h.

Figure 5.45. Schematic illustrating the mode of action of self-healing polymers through embedded healing-agent microcapsules that are activated by a propagating crack. Also shown is a polymeric microcapsule following rupture. Reproduced with permission from White, S. R. Sottos, N. R. Geubelle, R H. Moore, J. S. Kessler, M. R. Sriram, S. R. Brown, E. N. Viswanathan, S. Nature, 2001, 409, 794. Copyright 2001 Macmillan Magazines.

By being adsorbed in microcracks in the solid, it may reduce the mechanical work needed to fragment the particles of solid (Rebinder, 1947). These microcracks are believed to be formed in crystals under stress, but are self-healing and disappear when the stress is removed. The adsorption of surface-action agents onto the surfaces of these microcracks may increase their depth and reduce their self-healing ability and thus reduce the energy required to rupture solid particles mechanically. 

Association of Textile Chemists and Colorists recently [3] described the incorporation of small amoimts of fluorocarbon derivative in a polymeric material normally used to treat textiles for water repellency. They observed that the fluorocarbon preferentially adsorbed at the interfaces and decreased the values to 16 to 18 dynes per cm. Their films clearly showed the ability to self-heal, for when the initially adsorbed layer was deliberately scraped off, additional molecules quickly adsorbed at the interface when the polymer matrix was recured at an elevated temperature. The usefulness of adsorbed films of surface active molecules is thus apparent, and one may expect wide application of this technique to specific problems. The present study, in combination with previous investigations of wettability and surface activity in organic liquids, forms an excellent guide for the design and synthesis of further surface active agents for polymeric systems. 

The paper is devoted to development of novel approach to dope coatings with active anticorrosion species with self-healing ability. They contain nanoreservoirs which can store active agents and provide controllable release of them. The titania nanoparticles doped with cerium ions and organic inhibitors were used as nanocontainers to dope the hybrid sol-gel matrix and to provide long-term corrosion protection. 

Several other approaches are described by Ghosh [63]. The distance scales for which these self-healing repairs can be made already range from a few micrometres (healing agents) to a few millimetres (ionomers). Some early commercial applications of self-healing materials have been in automotive clear-coat paints... 

One of the strategies to manufacture a thermosetting self-repair material seems to be the storage of healing agents inside composites that restore the strength of the materials after damage. 

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