High-frequency rheology of a high viscosity silicone oil using diffusing wave spectroscopy

The flow inside a fluid damper where a piston reciprocates sinusoidally inside an outer casing containing high-viscosity silicone oil is simulated using a Finite Volume method, at various excitation frequencies. The oil is modelled by the Carreau-Yasuda (CY) and Phan-Thien & Tanner (PTT) constitutive equations. Both models account for shear-thinning but only the PTT model accounts for elasticity. The CY and other generalised Newtonian models have been previously used in theoretical studies of fluid dampers, but the present study is the first to perform full two-dimensional (axisymmetric) simulations employing a viscoelastic constitutive equation. It is found that the CY and PTT predictions are similar when the excitation frequency is low, but at medium and higher frequencies the CY model fails to describe important phenomena that are predicted by the PTT model and observed in experimental studies found in the literature, such as the hysteresis of the force-displacement and force-velocity loops. Elastic effects are quantified by applying a decomposition of the damper force into elastic and viscous components, inspired from LAOS (Large Amplitude Oscillatory Shear) theory. The CY model also overestimates the damper force relative to the PTT, because it underpredicts the flow development length inside the piston-cylinder gap. It is thus concluded that (a) fluid elasticity must be accounted for and (b) theoretical approaches that rely on the assumption of one-dimensional flow in the piston-cylinder gap are of limited accuracy, even if they account for fluid viscoelasticity. The consequences of using lower-viscosity silicone oil are also briefly examined. This is the accepted version of the article published in:

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Theoretical study of the flow in a fluid damper containing high viscosity silicone oil: Effects of shear-thinning and viscoelasticity

Syrakos

Dimakopoulos

Tsamopoulos

2018

Physics of Fluids

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Prevention of edge fracture using a nontoxic liquid metal sealant

2023

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Edge fracture, the sudden indentation of a viscoelastic fluid's free surface, often occurs when a sufficiently strong shear is applied to the fluid, rendering rheological measurements at high shear rates difficult. We show that sealing the fluid sample's free surface with liquid metal galinstan can delay fracture occurrence, extending the measurable shear rate range of a cone-and-plate fixture by around five times. The method's effectiveness is compared to the cone-partitioned plate fixture, an existing tool for mitigating sample fracture. Our cheap yet effective way to prevent edge fracture will benefit the general rheological study of complex fluids.

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Micronewton shear rheometer performing SAOS using 2 mg of sample

Luo

Ouyang

et al. 2022

Journal of Rheology

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Rheological measurements typically require at least 20–50 mg of sample. We set up a miniaturized sliding-plates shear rheometer (mgRheo) that requires only 2 mg sample or even less. We designed a flexure-based force-sensing device that could measure force ranging from the micronewton to millinewton scale, e.g., 40 μN–400 mN for one particular spring constant. The setup was strain-controlled by a piezostage and could perform standard rheological tests such as small amplitude oscillatory shear, step strain, and stress relaxation. The accuracy and consistencies were evaluated on polydimethylsiloxane viscoelastic standard, entangled poly(hexyl methacrylate), and polystyrene. The obtained phase angles quantitatively agreed with those from commercial rheometers. The exact values of the modulus are prone to the overfilling of the sample. The storage G′ and loss G″ moduli from the mgRheo were systematically higher than those from commercial rheometers (i.e., within 5% with careful trimming or 30% with excessive overfilling). Between 102 and 106 Pa, G′ and G″ were in good agreement with commercial rheometers. Such a setup allowed for general rheometric characterizations, especially obtaining linear viscoelasticity on soft matters that are synthetically difficult to obtain in a large quantity.

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High-frequency rheology of a high viscosity silicone oil using diffusing wave spectroscopy

Cited by 4 publications

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Theoretical study of the flow in a fluid damper containing high viscosity silicone oil: Effects of shear-thinning and viscoelasticity

Theoretical study of the flow in a fluid damper containing high viscosity silicone oil: Effects of shear-thinning and viscoelasticity

Prevention of edge fracture using a nontoxic liquid metal sealant

Micronewton shear rheometer performing SAOS using 2 mg of sample

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