Shear stress relaxation and physical aging study on simple glass-forming materials

Abstract

Relaxation and aging behaviors in three supercooled liquids: m-toluidine, glycerol, and sucrose benzoate have been studied by shear stress relaxation experiments in the time domain above and below their nominal glass transition temperatures. For the equilibrium state, the current study provides new data on the behavior of organic complex fluids. The shape of the relaxation function as characterized by the stretching exponent beta is discussed considering that a time-temperature master curve can be constructed even though the beta's for the individual response curves at each temperature vary systematically. In the nonequilibrium state, isothermal physical aging experiments at different glassy structures reveal that the effect of the aging process on the mechanical shear relaxation in these simple glass formers is similar to that observed in polymeric and other systems. Departure from the Vogel-Fulcher-Tamman behavior after the samples have aged back to equilibrium in the glassy state is observed for m-toluidine and, less strongly, for glycerol but not for sucrose benzoate. An inherent structure-based energy landscape concept is briefly discussed to account for the slow dynamics during the physical aging process.

Pressure relaxation of polystyrene and its comparison to the shear response

“…The data at the lowest measurements temperatures, below T g À10 8C, level off due to the fact that the samples did not attain equilibrium density during the 7-day aging prior to the commencement of the pressure relaxation experiments. On the other hand, the change in slope to what appears to be a weaker temperature dependence at temperatures just below T g (where equilibrium density is expected to be attained during the 7-day aging) is consistent with previous experimental [44][45][46][47][48][49] and theoretical work, [50][51][52] including our own experimental work on this same polystyrene. 18,20 We do note that in some reports 47,53,54 no deviation from WLF behavior is observed at temperatures below T g ; a more detailed discussion of the equilibrium temperature dependence near T g can be found elsewhere.…”

“…On the other hand, the change in slope to what appears to be a weaker temperature dependence at temperatures just below T g (where equilibrium density is expected to be attained during the 7-day aging) is consistent with previous experimental [44][45][46][47][48][49] and theoretical work, [50][51][52] including our own experimental work on this same polystyrene. 18,20 We do note that in some reports 47,53,54 no deviation from WLF behavior is observed at temperatures below T g ; a more detailed discussion of the equilibrium temperature dependence near T g can be found elsewhere. 47 To further compare the bulk and shear responses, we plot log[a B (P(t) À P o )] against the logarithm of the reduced time in the upper part of Figure 9 and plot the recoverable compliance of the shear response for the same polystyrene 16 in double logarithmic scale below.…”

“…18,20 We do note that in some reports 47,53,54 no deviation from WLF behavior is observed at temperatures below T g ; a more detailed discussion of the equilibrium temperature dependence near T g can be found elsewhere. 47 To further compare the bulk and shear responses, we plot log[a B (P(t) À P o )] against the logarithm of the reduced time in the upper part of Figure 9 and plot the recoverable compliance of the shear response for the same polystyrene 16 in double logarithmic scale below. The transition region in the bulk response occurs primarily in the short time region of the shear response and is finished by the time the Rouse modes become important in the shear response; this finding is consistent with the results of the dynamic modulus measurements on polystyrene and poly-(methyl methacrylate) by Kono 5 as well as the dynamic compliance on poly(vinyl acetate) by Deng and Knauss 6 although as discussed later, our interpretation of this finding differs from those of these researchers.…”

Replica theory of the rigidity of structural glasses

“…Linear response against shear deformations can be seen experimentally by measurements of the linear-viscosity (See for example [57][58][59][60]). In sec.…”

“…Whether it lies within the time window of experiments would depend on the specific systems under study [57][58][59][60].…”