Polystyrene temperature-dependent viscoelasticity

As expected, test temperatin-e will have a dramatic effect on the FCP kinetics of polymers owing considerably to their temperature-dependent viscoelastic nature. Indeed, studies of polystyrene and acrylonitrile-butadiene-styrene (ABS) have shown that FCP rates for given AX level generally decrease with decreasing test temperature (80). By contrast, a minimum FCP resistance was noted in polycarbonate and polysulfone at intermediate test temperatures (81,82). A complex test-temperatin-e response was also noted in studies on the influence... 

It was originally assumed that Gj should be proportional to T, and hence have a temperature dependence small compared to that for Xi, and further that all the Xi have a common dependence on temperatxure (7). Thus, it is assumed here that the temperature dependence of rj reflects that of only the T(. Recent investigators have suggested that for simple liquids, the Gf can have an appreciable temperatxure dependence xmder some conditions, so that it may be unreasonable to expect a simple fimction to correlate iq T) over extended temperature intervals 142a, 143b). Similar considerations may be necessary for a complete analysis of C as defined by Eq. (2.1) with temperature. Recent results of Plazek (777) showed that the temperature dependences of the viscous and recoverable contributions to the creep compliance of polystyrene are different from each other (after allowing for an expected proportionality of G,- to T). This can be interpreted as an indication of a significant temp>erature dependence of the G. Since our primary concern here is the temperature dependence of C for polymeric materials, for which the requisite data on deviation of Gj from proportionality to T do not exist, we will henceforth assume that there is only one contribution to the temperatiue dependence of (or of rj for simple liquids). Careful comparison of the temperature dependence of rj and of viscoelastic properties such as the recoverable compliance, may eventually provide an assessment of this assumption. 

While thermally assisted relaxations of polymers under stress are discussed in Chapter 5, where they play a dominant role in the viscoelastic response of polymers, we choose for consideration here glassy polystyrene to demonstrate the effects discussed above. Figure 4.2(a) shows the temperature dependence of the... 

The disparity between the temperature dependences of t and % [Eqs. (41) and (42)] depends on the size of the couphng parameter n. Polystyrene has a larger n (= 0.63) than polyisobutylene (= 0.45) [19, 96, 97]. Hence we expect the degree of breakdown of thermorheological simplicity is lesser in polyisobutylene (PIB) than polystyrene (PS).This expectation, as well as other predicted differences in viscoelastic properties of PIB and PS, were confirmed... 

Nevertheless, the difference between the temperature dependences of the terminal dispersion (or the viscosity) and the local segmental motion is significantly less for PIB than it is for PS. Dielectric-relaxation and PCS measurements (to be discussed later) have revealed that / (7 g) varies from polymer to polymer [34,164, 165,167,168], For example, polystyrene and polyisobutylene have a(.Tg) equal to 0.36 and 0.55, respectively [34,167,168]. This difference between the values of the stretching exponent j6a(7g) for polyisobutylene and polystyrene has been identified as the origin of their contrasting viscoelastic properties [169,170]. 

ABSTRACT - The fluorescence anisotropy decay (FAD) technique is first described, then the different expressions ich have been proposed for the orientation autocorrelation function (OACF) of polymer chains are presented. Typical FAD curves of dilute and concentrated solutions of polystyrene labelled with an anthracene group in the middle of the chain are compared to the various OACF expressions and discussed. In the case of bulk polybutadiene, FAD results obtained either on anthracene labelled chains or on 9,10 dialkylanthracene probes free in the polymer matrix, show that the same type of OACF as for polymer solutions can account for the experimental data. Besides, the temperature dependence of the correlation time of the labelled polybutadiene appears to agree with the WLF equation derived from macroscopic viscoelastic measurements, proving that the segmental motions of about 20 bonds which lead to the FAD of labelled polybutadiene participate in the glass transition processes of this polymer. 

Plazek, D. J. Temperature dependence of the viscoelastic behavior of polystyrene. / Phys. Chem. (1965) 69, pp. 3480-3487... 

Figure 12.16 Frequency dependence of G for narrow-distribution polystyrene L27 (molecular weight 167,000) at various temperatures. (Reprinted with permission fiom Onogi, S., T. Masuda, and K. Kitagawa Rheological Properties of Anionic Polystyrenes I. Dynamic Viscoelasticity of Narrow-Distribution Polystyrenes, Macromolecules, vol. 3, pp. 109-116, 1970. Copyright 1970 American Chemical Society.)...

The Finite Difference Method was employed to solve the coupled and non-linear partial differential equations. Prior to the simidation, temperature-dependent material properties and physical constants of the polystyrene-C02 system were collected [11-19]. At the initial expansion stage, the diffusion equation was first resolved. Then the mass change of blowing agent inside the cell was determined. Subsequently, the viscoelastic term was calculated by solving for the stress conponents based on the rheology equation. As a result, the cell size at the next time step could be understood. Time evolution would not cease until the cells got close to each other. During the... 

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