| The study of glass transition has been a hot issue in recent years.Small molecular liquids can be studied as the simplest material because of their strong glass forming ability.Using different means to study the same glass material,we can get more sufficient information to understand glass transition.In this paper,four alkyl phosphates（TMP,TEP,TPP,TBP）were studied by broadband dielectric spectroscopy and differential scanning calorimetry.The kinetic dielectric data fitted by HN equation,the glass transition temperature Tg-die,fragility md,stretching exponent?dand other parameters are compared with the thermodynamic corresponding parameters obtained by the TNMH fitting.The results show that the glass transition temperature Tg obtained by the two methods is basically equal,which means the relaxation behaviors of the molecules measured by two different means are both structure?relaxation.Previous studies have shown that the parameters obtained by different means are comparable.However,for TEP and TBP,the large difference between the dielectric md and enthalpic mH,as well as?dand?His a remarkable finding.By utilizing B?hmer’s correlation,it proves the results of enthalpy relaxation are more accurate,and the viscosity data of TBP also support the results of enthalpy relaxation.Through investigating the dipole distance of the molecules,we suggested that for the substances studied in this paper the polar concentrated in the molecular nucleus make the molecules easier to form dimers or trimers.While the dielectric relaxation only detects the local rotation,the enthalpy relaxation involves the whole molecule motion.This assumption has been further verified by the Kirkwood factor,which is consistent with previous studies that the enthalpy relaxation was regarded as the most fundamental relaxation to exhibit the non-Arrhenius and non-exponential behaviors.Finally,glass transition temperature Trgg is used to measure the glass forming ability of those substances. |
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