Self-healing break

The wide range of soHd lubricants can generally be classified as either inorganic compounds or organic polymers, both commonly used in a bonded coating on a matching substrate, plus chemical conversion coatings and metal films. Since solid-film lubricants often suffer from poor wear resistance and inabihty to self-heal any breaks in the film, search continues for improved compositions. 

Fuse, Liquid-Metal, Self-Healing. When mercury replaces the filament of an exploding-wire fuse, it. will break contact by vaporizing upon application of an overvoltage, then make contact by condensing when (he overload disappears. This happens within a heavy-walled capillary tube connecting two reservoirs (see sketch). Evaporation forces mercury from the capillary to break the. circuit Experimental quartz glass and pyrex tubes exhibit da-... 

FIGURE 60.18 (See color insert.) (a) Principle of self-healing system basically solution, (b) After provoking stress cracks, microcapsules will break and the core content refills the capillaries. (From White, S.R. and Sottos, N.R., Nature, 409, 794, 2001.)... 

The most important sources of fluctuation in tan-taliun capacitors consist in regenerative micro breaks, fluctuation of polarization and mechanical strain. The frequency dependence of the noise spectral density in mHz region gives the information on slow irreversible processes of tantalum pentoxide crystallizations and oxide reduction. The self-healing process can improve... 

Figure 12.5. Photographs of TDS cross-linked polymer in self-healing reaction, a) Before self-healing reaction, b) after cutting cross-linked polymer and c) after self-healing reaction for 24 h. d) Stress-strain curve and e) elongation value at break (%) of cross-linked polymer after irradiation of visible light at room temperature over time. Reproduced with permission from[AMA 12b]...

Another approach is the use of encapsulated solvents included in soluble conductive polymers. Capsules will break upon damage, dissolve the matrix and restore the electrical contact between phases once the solvent has evaporated (Odom et al., 2012) as can be observed by the electrical conductivity test in Fig. 9.6e in which a drop of potential is detected when the system is damaged and restored after a period of time when a self-healing system is employed. The restoration of electrical (and thermal) conductivities is expected to significantly grow in the near future due to the broad application in many different fields. 

In these systems capsules are broken upon damage and reactive monomers that are able to close the scratch fill the break. Another possibility is the function of the polymers that show reversible bond breakage and formation. Examples are groups that can undergo Diels-Alder reactions such as maleimide and furan rests. Sol-gel-derived sihca particles that contain these groups can be used for the preparation of self-healing nanocomposites [56]. 

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