Ionic Interactions Induced Anomalous Segmental Dynamics in Polymer/Salt Complexes

Dynamic fragility (m) is reported to be inversely proportional to the stretching parameter (β) in many cases. Herein, their relation is further investigated in polyacrylate/salt complexes with ionic interactions. The introduction of metallic ions leads to a decreased enthalpy hysteresis and increased storage modulus at the glassy state, revealing that the ionic interactions act as physical cross-linkers. Further results found a reduced β value and a larger difference in relaxation time between segmental and secondary relaxation. Surprisingly, an anomalous decrease of fragility accompanied by the increase of the glass transition temperature is observed in all complexes. Moreover, the m value further decreases for the α′-relaxation corresponding to the restricted motions in the vicinity of ionic clusters in complex with flexible chains. We suppose that the polarities of metallic ions make extra contributions to the enthalpy change of segmental motions, thereby playing a decisive role in the activation free energy of segmental cooperative rearrangement. Most importantly, the glass transition width can be broadened significantly given that m and β decrease simultaneously, thus providing a new strategy to fabricate high-performance damping materials.