Studies of non-exponentiality of structural relaxation in glass forming liquids:a review

The non-exponential behavior is one of the three canonical characters of structural relaxation dynamics in supercooled liquids.The non-exponential dynamics of various glass-formers covering molecular,metallic,polymeric,network and ionic systems is reviewed across the whole liquid region from glass transition.General rules are outlined from the glass forming liquids.It is found that the majority of glass forming liquids is subject to the time-temperature-superposition(TTS) law at low dynamic regimes,while the width of the TTS regime depends on liquid fragility.The exponential mode is reached for all the liquids at fast dynamic regions with a critical relaxation frequency of ～1011 Hz(equivalent to a relaxation time of 1.6×10 12 s).The correlations of the non-exponential parameter with liquid fragility and the width of TTS regimes are discussed,and dielectric and enthalpy relaxations are highlighted.