molecule. It is likely to suppose that the connection between aand b-dynamics is not a universal feature of all b-processes, but only of those local processes intimately connected to the cooperative structural dynamics. DGEBA present two b-processes, and it would be important to check this idea not only on the slower bprocess but also on the faster g-process. However, since experimental limitation the g-process was not measured at high pressure and such test cannot be done. However, to support the idea that such type of investigation can distinguish b-processes with a particular origin, we can refer to data of decahydroisoquinoline in, ref [12]. This result was also found in some different systems. The different temperature and pressure paths of mixtures containing the rigid polar molecule quinaldine (QN) (obtained from Aldrich, Tg = 180 K) and tristyrene (obtained from PSS, Tg = 234 K), with concentration ranging from 5 to 100 wt%. Tristyrene was mixed well with QN, and was studied for being used as the non active component in dielectric measurements because of the weak dipole moment of repeat unit, Figure 6, ref. [12].

5. CONCLUSION

We investigated the relation between secondary and structural dynamics of diglycidyl ether of bisphenol-A (DGEBA) under variations of temperature and pressure. We propose a model independent analysis for scrutiny a possible relation between structural and secondary relaxations. The analysis consists in investigating the ratio ta/tb for different values of pressure and temperature (density and thermal energy), but the same value of structural relaxation time. According to such analysis we evidenced that the b-process in DGEBA is clearly related with the structural dynamics, and then to the glass transition. In fact, for different thermodynamic conditions of pressure and temperature corresponding to for DGEBA, we observe that the relaxation time of the

Figure 6. Relaxation map for the mixture 10% QN in tristyrene. (a) Isobaric data: 0.1 MPa (stars), 380 MPa (circles). (b) Isothermal data: 238 K (stars), 253 K (circles), 263 K (squares), 278 K (triangles). Closed and open symbols are for ta and tJG respectively. Continuous lines through the ta data represent Vogel-Fulcher fits in (a), and linear fits in (b). The dashed-dotted line through tJG in (a) is an Arrhenius fit to the ambient pressure data at T < Tg, and the dashed curves in (b) are guides for eyes in following its P-dependence. Upper and lower horizontal dotted lines indicate log10(ta) = –0.17 (i.e. ta = 0.67 s) and log10(tJG) = –5.46 (tJG = 3.5 ms), vertical dotted lines mark the corresponding x-axis values. Vertical arrows correspond to the values of x-axis for which log10(ta) = 3 and mark the change of dynamics for tJG, ref. [12].

b-process is almost constant. These results are fully consistent with those contemporarily found for mixtures of glass formers materials.

6. ACKNOWLEDGEMENTS

This work was supported by the University of Sistan and Baluchestan.

REFERENCES

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