Self-Healing of Unentangled Polymer Networks withReversible Bonds.

Self-healing polymeric materialsare systems that after damagecan revert to their original state with full or partial recovery ofmechanical strength. Using scaling theory we study a simple modelof autonomic self-healing of unentangled polymer networks. In thismodel one of the two end monomers of each polymer chain is fixed inspace mimicking dangling chains attachment to a polymer network, whilethe sticky monomer at the other end of each chain can form pairwisereversible bond with the sticky end of another chain. We study thereaction kinetics of reversible bonds in this simple model and analyzethe different stages in the self-repair process. The formation ofbridges and the recovery of the material strength across the fracturedinterface during the healing period occur appreciably faster aftershorter waiting time, during which the fractured surfaces are keptapart. We observe the slowest formation of bridges for self-adhesionafter bringing into contact two bare surfaces with equilibrium (verylow) density of open stickers in comparison with self-healing. Theprimary role of anomalous diffusion in material self-repair for shortwaiting times is established, while at long waiting times the recoveryof bonds across fractured interface is due to hopping diffusion ofstickers between different bonded partners. Acceleration in bridgeformation for self-healing compared to self-adhesion is due to excessnonequilibrium concentration of open stickers. Full recovery of reversiblebonds across fractured interface (formation of bridges) occurs afterappreciably longer time than the equilibration time of the concentrationof reversible bonds in the bulk. [ABSTRACT FROM AUTHOR]