Ionic Interactions Induced Anomalous Segmental Dynamics\nin Polymer/Salt Complexes

Dynamic\nfragility (<i>m</i>) is reported to be inversely\nproportional to the stretching parameter (β) in many cases.\nHerein, their relation is further investigated in polyacrylate/salt\ncomplexes with ionic interactions. The introduction of metallic ions\nleads to a decreased enthalpy hysteresis and increased storage modulus\nat the glassy state, revealing that the ionic interactions act as\nphysical cross-linkers. Further results found a reduced β value\nand a larger difference in relaxation time between segmental and secondary\nrelaxation. Surprisingly, an anomalous decrease of fragility accompanied\nby the increase of the glass transition temperature is observed in\nall complexes. Moreover, the <i>m</i> value further decreases\nfor the α′-relaxation corresponding to the restricted\nmotions in the vicinity of ionic clusters in complex with flexible\nchains. We suppose that the polarities of metallic ions make extra\ncontributions to the enthalpy change of segmental motions, thereby\nplaying a decisive role in the activation free energy of segmental\ncooperative rearrangement. Most importantly, the glass transition\nwidth can be broadened significantly given that <i>m</i> and β decrease simultaneously, thus providing a new strategy\nto fabricate high-performance damping materials.