Mastering Superior Performance Origins of Ionic Polyurethane/Silica Hybrids

Abstract

Even though reversible interactions within ionic hydrogels are well-studied, underlying mechanisms responsible for the high-value added performance of ionic nanocomposites remain almost unexplored. We herein propose a fundamental understanding aiming at elucidating the mechanism behind the reversible breaking and reformation of ionic bonding in the case of organic–inorganic hybrids made of a combination of imidazolium-functionalized poly(ethylene glycol)-based polyurethane (im-PU) and surface-modified sulfonate silica nanoparticles (SiO2–SO3H). Such ionic hybrids already demonstrated unique features related to the presence of electrostatic interactions, but the underlying mechanisms governing the overall material performance have never been discussed. To dissociate the reinforcement role of nanoparticles and ionic interactions, either standard nonionic SiO2 or ionic SiO2–SO3H nanoparticles were introduced into im-PU. Mechanical performances, thermal transitions, relaxation processes, and the morphology of the hybrids were deeply investigated to better comprehend the mechanisms at the origin of the ionic material reinforcement. In addition, a mechanistic investigation is proposed to quantify the dissipation energy ability of the as-proposed ionic hybrids, and an approach is presented to identify a characteristic time for restoration of reversible ionic bonds under different loading scenarios.