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Z. Kokuti, L. Volker-Pop, M. Brandstatter, J. Kokavecz, P. Ailer, L. Palkovics, G. Szabo, A. Czirjak
Exploring the nonlinear viscoelasticity of a high viscosity silicone oil with LAOS
Appl. Rheol. 26:1 (2016) 14289 (9 pages) ►

Measurements and modeling of the nonlinear viscoelastic properties of a high viscosity silicone oil (polydimethylsiloxane, PDMS) are reported. LAOS test were performed with a high precision rotational rheometer to probe the nonlinear response. The measurements show that the material can be safely considered linear below strain amplitude 1. The viscous Lissajous-Bodwitch curves indicate intracycle shear thinning, whereas the elastic Lissajous-Bodwitch curves indicate intracycle strain stiffening in the nonlinear regime. Secondary loops in some of the measured viscous stress curves are attributed to a non-sinusoidal shear rate signal. A multi-element White-Metzner model is used as a constitutive equation, which accurately describes the LAOS data in all measured cases. Based on the extension of the measured data by simulations, nonlinear properties are analyzed both for the elastic and for the viscous part. It is observed that the nonlinearity considerably increases the weight of the higher harmonics in the shear stress signal. It is predicted that the viscous nonlinearity has a maximum around 50 rad/s angular frequency, and that the elastic nonlinearity becomes nearly independent of the angular frequency above 30 rad/s.

► Cite this publication as follows:
Kokuti Z, Volker-Pop L, Brandstatter M, Kokavecz J, Ailer P, Palkovics L, Szabo G, Czirjak A: Exploring the nonlinear viscoelasticity of a high viscosity silicone oil with LAOS, Appl. Rheol. 26 (2016) 14289.

Z. Kokuti, K. van Gruijthuijsen, M. Jenei, G. Toth-Molnar, A. Czirjak, J. Kokavecz, P. Ailer, L. Palkovics, A. C. Volker, G. Szabo
High-frequency rheology of a high viscosity silicone oil using diffusing wave spectroscopy
Appl. Rheol. 24:6 (2014) 63984 (7 pages) ►

Measurements and modeling of rheological properties of a high viscosity silicone oil (polydimethylsiloxane, PDMS) at high frequency are reported. The linear viscoelastic properties are measured by small amplitude oscillation shear (SAOS) tests with a rotational rheometer. Furthermore, Diffusing Wave Spectroscopy (DWS) is used, which expands the angular frequency range of the measured loss and storage moduli up to 10⁵ rad/s, in a temperature range of 20 - 70 C. Good agreement between both methods is found in the overlapping frequency region, especially at higher temperatures. The DWS data show that the elastic modulus stays dominant and increases with frequency, without a second cross-over point up till 10⁸ rad/s. Flow curves, measured with rotational and with capillary rheometry up to a shear rate of 7.6 × 10⁴ s^-1, show shear thinning behavior, which implies nonlinear viscoelasticity. Comparison of the dynamic and complex viscosity shows that the Cox-Merz rule is valid in a frequency range spanning six orders of magnitude. A multi-element White-Metzner model is proposed as a constitutive equation, which accurately describes the nonlinear viscoelastic properties, including the decrease of the loss and storage moduli during amplitude sweeps in oscillatory shear measurements.

► Cite this publication as follows:
Kokuti Z, vanGruijthuijsen K, Jenei M, Toth-Molnar G, Czirjak A, Kokavecz J, Ailer P, Palkovics L, Volker AC, Szabo G: High-frequency rheology of a high viscosity silicone oil using diffusing wave spectroscopy, Appl. Rheol. 24 (2014) 63984.

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