TTS in LAOS: validation of time-temperature superposition under large amplitude oscillatory shear

Abstract

The validation of time-temperature superposition (TTS) of non-linear parameters obtained from large amplitude oscillatory shear (LAOS) is investigated for a model viscoelastic fluid. Oscillatory time sweeps were performed on a 11 wt% solution of high molecular weight polyisobutylene in pristane as a function of temperature and frequency and for a broad range of strain amplitudes varying from the linear to the highly non-linear regime. Lissajous curves show that this reference material displays strong non-linear behavior when the strain amplitude is exceeding a critical value. Elastic and viscous Chebyshev coefficients and alternative non-linear parameters were obtained based on the framework of Ewoldt et al. ( 2008) as a function of temperature, frequency, and strain amplitude. For each strain amplitude, temperature shift factors a T (T) were calculated for the first order elastic and viscous Chebyshev coefficients simultaneously, so that master curves at a certain reference temperature T ref were obtained. It is shown that the expected independency of these shift factors on strain amplitude holds even in the non-linear regime. The shift factors a T (T) can be used to also superpose the higher order elastic and viscous Chebyshev coefficients and the alternative moduli and viscosities onto master curves. It was shown that the Rutgers-Delaware rule also holds for a viscoelastic solution at large strain amplitudes.

A DMA study of the interfacial changes on injection‐molded iPP/mica composites modified by a p‐phenylen‐bis‐maleamic acid grafted atactic polypropylene

“…Further, studies related to that strong mechanical interaction level at the iPP/mica interface in the 75/25 PP/mica injection molded composite are in progress now. In advance, we can say that so sharp damping responses in the pristine 75/25 iPP/mica composites disappear according to new DMA tests based on annealing effects, while no significant pattern differences are observed by varying the test frequency always inwards the low testing frequency range . Just as an example, the plots displayed in the Figure let confirm that the 75/25 iPP/mica composite maintain the pattern in the damping responses, but appearing downwards shifted (as expected) with increasing test frequencies, equally than all the other composites and the pristine iPP.…”

Molecular dynamics simulations of crystal nucleation in entangled polymer melts under start-up shear conditions

“…namics trajectories at the desired temperatures. From these trajectories, we calculate the stress relaxation modulus (G(t)) and then we shift all curves to the reference temperature curve based on the time-temperature superposition (TTS) concept 87,88 using the same approach as widely used for experimental data [88][89][90][91][92][93][94] . We apply TTS to G(t) in the following way:…”

“…This relation gives a good fit of the data in the plateau and terminal zones for temper-atures well above the glass transition temperature T g , which has been reported as 223.04 ± 0.22K 43 for this force field. The temperature dependence of the horizontal shift factor a T for a temperature range between T g and T g + 100 K can be expressed by the Williams-Landel-Ferry (WLF) equation 91,95 :…”

Microsecond relaxation processes in shear and extensional flows of weakly elastic polymer solutions

“…Regular rotational rheometry can therefore not be used to characterize their relaxation behaviour, in particular since the applicability of time-temperature superposition is limited due to the low flow activation energy of polymer solutions [Vananroye et al (2011)] and the sensitive nature of these fluids prevents measurements over a wide temperature range. In order to access the low relaxation times in the present work, a piezo-axial vibrator (PAV) has been used.…”