Microrheology and structure of a yield-stress polymer gel

Oppong, Felix K.; Rubatat, Laurent; Frisken, Barbara J.; Bailey, Arthur E.; Bruyn, John R. de

doi:10.1103/physreve.73.041405

Cited by 109 publications

(92 citation statements)

References 47 publications

(43 reference statements)

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“…This is, in fact, also the interpretation shared in the literature for carbopol microstructure, which is observed to be formed of elastic spongelike elements [27,28]. Therefore, instead of using an abstract structure parameter (with no direct physical interpretation) it is more sensible to select the immobilized volume fraction φ, which describes the jammed fluid, as has been done in approaches using the population balance equations [26].…”

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confidence: 77%

Transient shear banding in time-dependent fluids

et al. 2013

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We study the dynamics of shear-band formation and evolution using a simple rheological model. The description couples the local structure and viscosity to the applied shear stress. We consider in detail the Couette geometry, where the model is solved iteratively with the Navier-Stokes equation to obtain the time evolution of the local velocity and viscosity fields. It is found that the underlying reason for dynamic effects is the nonhomogeneous shear distribution, which is amplified due to a positive feedback between the flow field and the viscosity response of the shear thinning fluid. This offers a simple explanation for the recent observations of transient shear banding in time-dependent fluids. Extensions to more complicated rheological systems are considered. The property that characterizes complex fluids is their nontrivial rheology, shear rate-stress relation. They are generally further categorized into shear thinning or shear thickening fluids. Both cases are additionally complicated by time dependence. Due to the stress-shear interaction, already small perturbations in the local stress can result in a positive feedback with the flow promoting shear instabilities in each case [1,2]. The understanding of complex fluids is of enormous importance for many practical applications [3] and the theory touches on many branches of physics. Recent advances make it possible to follow the suspension local velocity during a standard rheological experiment [4,5]. Quantifying the local flow field simultaneously with rheological measurements gives the possibility to measure both the intrinsic and apparent rheology. This has led to the discovery that a heterogeneous shear distribution in samples during such tests is ubiquitous. Shear banding [6] has been observed in many systems composed of substantially different building blocks, such as colloidal glasses, wormlike micelles, foams, and granular matter [7]. The current viewpoint, both phenomenologically and theoretically, is that a nonmonotonic intrinsic flow curve is what is common to most of these materials [6,8], but also other mechanisms have been suggested [9].A branch of complex fluids are the simple yield stress fluids [10]. These materials do not show aging phenomena (thixotropy). Therefore, they are expected to have a monotonic intrinsic flow curve and a steady state without shear bands [11]. However, recent experiments [12] display shear banding during startup flows in a rotational rheometer indicating timedependent behavior. These so called transient shear bands can be very long lasting, but eventually vanish with a homogeneous steady state. The transient shear banding phenomenon tests our fundamental understanding of non-Newtonian fluids, and is also important for industrial processes and simply for understanding usual rheological measurements. A particular feature of the transient shear banding is that it appears to exhibit scaling familiar from critical phenomena: The time it takes for the transient to disappear (fluidization time τ f ) is a power-law functi...

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confidence: 77%

Transient shear banding in time-dependent fluids

et al. 2013

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“…Oppong et al [30], Oppong and de Bruyn [29]) and r % 1 Pa which leads to fþ D 2k B T % 240. These simple numerical estimates indicate that, in the case of a percolated Carbopol Ò gel structure, one should not expect the simplified Arrhenius law to apply in the whole range of temperatures and one should consider instead the full Eyring dependence given by Eq.…”

Section: A Possible Qualitative Explanation For the Anomalous Temperamentioning

confidence: 95%

Thermorheological properties of a Carbopol gel under shear

Weber

Moyers-González

Burghelea

2012

Journal of Non-Newtonian Fluid Mechanics

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“…The statistical analysis to calculate the representative MSD was based on a number over 1000 bacterial cells and particles. Because MSD can only be obtained from 20 to 30% of the total measurement time [19], the motion information from only 10 s of the total measurement time (50 s) was used for the MSD calculation. Additionally, the root MSD was also used for quantitative comparison of the oscillational motion in regard to the real moving distance.…”

Section: Msd Using the Particle Tracking Methodsmentioning

confidence: 99%