Time-temperature equivalence in a PVA dual cross-link self-healing hydrogel

Abstract

Hydrogels consisting of permanent chemical bonds plus transient physical bonds are known to have self-healing properties, high toughness, and to be highly viscoelastic. These mechanical responses derive from the ability of the physical bonds to break and reform during deformation. The rate of bond breaking and reformation is found experimentally to be independent of stress but is expected to depend on temperature. Using a poly(vinyl alcohol) hydrogel with chemical and physical cross links, the temperature dependence of the mechanical response is measured using large strain load/unload tension tests and torsional rheometry for temperatures from 13 to 50 °C. The rheometry data show that time-temperature superposition can be used to condense the data to a master curve. It is found that allowing the model parameters to be temperature dependent, a previously developed constitutive model fits the tension and rheometry data well. Horizontal (time) and vertical (amplitude) shift factors calculated directly from the rheometer test data and from tension test data agree well with each other showing that the constitutive model describes the mechanical behavior well over the temperature range explored and that the material closely follows simple time-temperature superposition.Hydrogels consisting of permanent chemical bonds plus transient physical bonds are known to have self-healing properties, high toughness, and to be highly viscoelastic. These mechanical responses derive from the ability of the physical bonds to break and reform during deformation. The rate of bond breaking and reformation is found experimentally to be independent of stress but is expected to depend on temperature. Using a poly(vinyl alcohol) hydrogel with chemical and physical cross links, the temperature dependence of the mechanical response is measured using large strain load/unload tension tests and torsional rheometry for temperatures from 13 to 50 °C. The rheometry data show that time-temperature superposition can be used to condense the data to a master curve. It is found that allowing the model parameters to be temperature dependent, a previously developed constitutive model fits the tension and rheometry data well. Horizontal (time) and vertical (amplitude) shift factors calculated directly from t...