Self-Healing Behaviors of Tough Polyampholyte Hydrogels

Abstract

Recently,\npolyampolytes have been discovered to form hydrogels\nthat possess high toughness, full resilience, and self-healing between\ntwo cut surfaces. The self-healing of this class of hydrogels is based\non the re-forming of the multiple ionic bonds at the fractured surfaces,\nin which the mobility of the polymer segments and strength of the\nionic bonds play an important role. In this work, we study the effects\nof healing temperature and chemistry of the polyampholyte hydrogels\n(chemical cross-linker density and chemical structure of the monomers)\non the healing kinetics and healing efficiency. The high healing temperature\nsubstantially accelerates the self-healing kinetics. Chemical cross-linking\nreduces the self-healing efficiency. Monomers with more hydrophobic\nfeature give a low self-healing efficiency. For polyampholyte physical\nhydrogels with a softening temperature below the room temperature,\nexcellent healing efficiency (∼84% on average and maximum 99%)\nwas observed without any external stimuli. We found a correlation\nbetween the self-healing efficiency and the fraction of dynamic bonds\nin the total bonds for relatively soft samples, which is an evidence\nthat the self-healing is due to the re-forming of dynamic bonds.