| Popis: |
Interdiffusion of partial chains, which can be regarded as localized flow, repairs a mechanically induced damage. For example, dangling chains in a weak gel show interdiffusion and thus provide entanglement couplings, leading to mechanical strength, that is, repairing. In fact, a critical gel just beyond the sol–gel transition point, that has a lot of dangling chains, shows good healing property in a short time without manual operation beyond the glass transition temperature Tg. Moreover, it does not show macroscopic flow because of the permanent network structure. However, such materials usually exhibit low modulus due to fewer cross-link points and adhesive nature originated from dangling chains. One of the methods to overcome the problems is to enhance Tg. Although the healing performance is limited for a critical gel with high Tg, a shallow scar is healed in a short time because the segmental motion is enhanced at surface due to excess amount of free volume. It is also possible to avoid the problems using a crystalline polymer. In this case, healing of a critical gel with crystallites is performed by ironing. Moreover, a crystalline polymer with low crystallinity and a thermoplastic elastomer composed of a triblock copolymer with a small amount of hard segment exhibit autonomic healing behavior at cut surface. This is attributed to the increase in the amorphous chains with marked segmental motions at cut surface, which are generated by the destruction of structure, such as crystallite and phase-separation, by sudden deformation at cutting. Finally, healing of surface scar on a glassy plastic is demonstrated, at which surface plasticization by moisture accelerates the healing. |
