Continuous relaxation spectra for constitutive models in medium-amplitude oscillatory shear

2018 ◽  
Vol 62 (5) ◽  
pp. 1271-1298 ◽  
Author(s):  
Luca Martinetti ◽  
Johannes M. Soulages ◽  
Randy H. Ewoldt
Keyword(s):  
Constitutive Models ◽  
Oscillatory Shear ◽  
Relaxation Spectra ◽  
Continuous Relaxation ◽  
Medium Amplitude Oscillatory Shear

Spectral method for time-strain separable integral constitutive models in oscillatory shear

2021 ◽  
Vol 33 (11) ◽  
pp. 113104
Author(s):  
Sachin Shanbhag ◽  
Shivangi Mittal ◽  
Yogesh M. Joshi
Keyword(s):  
Spectral Method ◽  
Constitutive Models ◽  
Oscillatory Shear

scholarly journals Time-strain separability in medium-amplitude oscillatory shear

2019 ◽  
Vol 31 (2) ◽  
pp. 021213 ◽  
Author(s):  
Luca Martinetti ◽  
Randy H. Ewoldt
Keyword(s):  
Oscillatory Shear ◽  
Medium Amplitude Oscillatory Shear

scholarly journals Intra-Cycle Elastic Nonlinearity of Nitrogen-Doped Carbon Nanotube/Polymer Nanocomposites under Medium Amplitude Oscillatory Shear (MAOS) Flow

Nanomaterials ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1257 ◽  
Author(s):  
Milad Kamkar ◽  
Soheil Sadeghi ◽  
Mohammad Arjmand ◽  
Ehsan Aliabadian ◽  
Uttandaraman Sundararaj
Keyword(s):  
Rheological Properties ◽  
Polymer Nanocomposites ◽  
Polyvinylidene Fluoride ◽  
Viscoelastic Behavior ◽  
Oscillatory Shear ◽  
Dispersed Systems ◽  
Nitrogen Doped ◽  
Elastic Nonlinearity ◽  
Medium Amplitude Oscillatory Shear ◽  
Nitrogen Doped Carbon

This study seeks to unravel the effect of carbon nanotube’s physical and chemical features on the final electrical and rheological properties of polymer nanocomposites thereof. Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized over two different types of catalysts, i.e., Fe and Ni, employing chemical vapor deposition. Utilizing this technique, we were able to synthesize N-CNTs with significantly different structures. As a result, remarkable differences in the network structure of the nanotubes were observed upon mixing the N-CNTs in a polyvinylidene fluoride (PVDF) matrix, which, in turn, led to drastically different electrical and rheological properties. For instance, no enhancement in the electrical conductivity of poorly-dispersed (N-CNT)Ni/PVDF samples was observed even at high nanotube concentrations, whereas (N-CNT)Fe/PVDF nanocomposites exhibited an insulative behavior at 1.0 wt%, a semi-conductive behavior at 2.0 wt%, and a conductive behavior at 2.7 wt%. In terms of rheology, the most substantial differences in the viscoelastic behavior of the systems were distinguishable in the medium amplitude oscillatory shear (MAOS) region. The stress decomposition method combined with the evaluation of the elastic and viscous third-order Chebyshev coefficients revealed a strong intra-cycle elastic nonlinearity in the MAOS region for the poorly-dispersed systems in small frequencies; however, the well-dispersed systems showed no intra-cycle nonlinearity in the MAOS region. It was shown that the MAOS elastic nonlinearity of poorly-dispersed systems stems from the confinement of N-CNT domains between the rheometer’s plates for small gap sizes comparable with the size of the agglomerates. Moreover, the intra-cycle elastic nonlinearity of poorly-dispersed systems is frequency-dependent and vanished at higher frequencies. The correlation between the microstructure and viscoelastic properties under large shear deformations provides further guidance for the fabrication of high-performance 3D-printed electrically conductive nanocomposites with precisely controllable final properties for engineering applications.

scholarly journals Small and Medium Amplitude Oscillatory Shear Rheology of Model Branched Polystyrene (PS) Melts

Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 365
Author(s):  
Hyeong Yong Song ◽  
Lorenz Faust ◽  
Jinha Son ◽  
Mingeun Kim ◽  
Seung Joon Park ◽  
...  
Keyword(s):  
Low Frequency ◽  
Oscillatory Shear ◽  
Zero Shear Viscosity ◽  
Plateau Modulus ◽  
Intrinsic Nonlinearity ◽  
Linear Viscoelastic ◽  
The Difference ◽  
Total Molecular Weight ◽  
Branched Polystyrene ◽  
Medium Amplitude Oscillatory Shear

Linear and nonlinear rheological properties of model comb polystyrenes (PS) with loosely to densely grafted architectures were measured under small and medium amplitude oscillatory shear (SAOS and MAOS) flow. This comb PS set had the same length of backbone and branches but varied in the number of branches from 3 to 120 branches. Linear viscoelastic properties of the comb PS were compared with the hierarchical model predictions. The model underpredicted zero-shear viscosity and backbone plateau modulus of densely branched comb with 60 or 120 branches because the model does not include the effect of side chain crowding. First- and third-harmonic nonlinearities reflected the hierarchy in the relaxation motion of comb structures. Notably, the low-frequency plateau values of first-harmonic MAOS moduli scaled with M w − 2 (total molecular weight), reflecting dynamic tube dilution (DTD) by relaxed branches. Relative intrinsic nonlinearity Q0 exhibited the difference between comb and bottlebrush via no low-frequency Q0 peak of bottlebrush corresponding to backbone relaxation, which is probably related to the stretched backbone conformation in bottlebrush.

Numerical Studies of the Effect of Constitutive Model Parameters as Reflecting Polymer Molecular Structure on Extrudate Swell

2002 ◽  
Vol 12 (5) ◽  
pp. 252-259 ◽  
Author(s):  
Nattapong Nithi-Uthai ◽  
Ica Manas-Zloczower
Keyword(s):  
Molecular Weight ◽  
Constitutive Model ◽  
Full Range ◽  
Constitutive Models ◽  
Model Parameters ◽  
Extrudate Swell ◽  
Relaxation Spectra ◽  
Shear Rates ◽  
Swell Ratio ◽  
Numerical Predictions

Abstract PolyFlow, a software package based on the finite element method was employed to simulate the extrudate swell for polybutadiene of various molecular weight (Mw) and molecular weight distribution (MWD). We calculated the relaxation spectra for the different samples and then inserted the spectra into a standard K-BKZ constitutive model used in the numerical simulations. Accurate predictions of MWD confirm the completeness of frequency range in the oscillatory shear experimental data. In turn, the wholeness of relaxation spectra as substantiated by MWD predictions, sustain the level of confidence when using constitutive models based on these spectra. We demonstrate the importance of using the full range of relaxation spectrum rather than a short range around typical shear rates for the accuracy of the numerical predictions. We found extrudate swell ratio (ESR) to be strongly dependent on MWD and stress conditions at the die exit.

Frequency-sweep medium-amplitude oscillatory shear (MAOS)

2018 ◽  
Vol 62 (1) ◽  
pp. 277-293 ◽  
Author(s):  
Piyush K. Singh ◽  
Johannes M. Soulages ◽  
Randy H. Ewoldt
Keyword(s):  
Oscillatory Shear ◽  
Frequency Sweep ◽  
Medium Amplitude Oscillatory Shear

On the use of continuous relaxation spectra to characterize model polymers

2016 ◽  
Vol 60 (6) ◽  
pp. 1115-1120 ◽  
Author(s):  
Scott Ankiewicz ◽  
Nese Orbey ◽  
Hiroshi Watanabe ◽  
Helen Lentzakis ◽  
John Dealy
Keyword(s):  
Relaxation Spectra ◽  
Continuous Relaxation
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