Effect of thermodynamic history on secondary relaxation in glassy phenolphthalein-dimethyl-ether

Abstract

We present a study of the intermediate secondary relaxation process of phenolphthalein-dimethyl-ether. Though this process is intramolecular in nature, it reveals pronounced pressure dependence. Moreover, its relaxation frequency and intensity exhibit pronounced dependence on the thermal history followed during vitrification. These results suggest that the nonequilibrium nature of the glassy state influences this secondary relaxation principally through the dependence on the specific volume

Effect of thermodynamic history on secondary relaxation in the glassy state

“…The values of temperature and pressure at which the systems were vitrified along path A were estimated according to unpublished data of PPG400 and the data reported in Refs. [13,20,22] for the other samples (Table1). The maximum error is around ±5%.…”

“…Representative spectra of the other systems can be found in Refs. [13,18,[20][21][22][23][24]. The secondary relaxation was analyzed in terms of the symmetric ColeCole function.…”

“…Another consequence of the nonequilibrium condition of glasses is that thermodynamic and relaxation properties show different values when measured in the glassy state at fixed thermodynamic condition subsequently to different vitrification histories [7][8][9]. For example, this was observed for the relaxation frequency of several secondary processes [3,10] consequently to cooling with different rates, or after vitrification combining different sequences of cooling and compression steps [11][12][13]. The reason why secondary processes are influenced by the thermodynamic history of the glass is not clear at all, and the microscopic mechanisms at the basis of such dependence are unknown.…”

“…Despite the compact molecular structure, all the systems present a complex relaxation scenario. Glassy PDE presents three different relaxation processes: a so called excess wing, and two secondary relaxations [18,19], that are interpreted in term of local motions of parts of the molecule [13,18,19]. Glassy PPGE shows two secondary processes, the slower being of JG type [20,21], and the faster probably related to local motion of the epoxy subunits.…”

Polarization fluctuations in an epoxy system above and below the glass transition

“…Systems characterized by slow dynamics can be driven out of thermodynamic equilibrium by means of a rapid change of appropriate external variables. For instance glassy materials are never in an equilibrium state, and a glass former can be driven to an out of equilibrium state by a sudden temperature or pressure jump taking it into the glassy state [2,3,4]. After such treatment, the glass spontaneously tends to the equilibrium state, and the response function of the system depends on the time elapsed from the formation of the glass, t w , as for example it is reflected in the time evolution of dielectric spectra of glass formers after a temperature jump in the glassy state [2,3,5].…”