Shear-induced changes of electrical conductivity in suspensions

Crawshaw, John; Meeten, G.H.

doi:10.1007/s00397-006-0113-3

Cited by 7 publications

(6 citation statements)

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“…Description of the test fixture Rheo-electric platforms typically involve coupling an electrical measuring system to a conventional torsional rheometer that is used to measure the rheological properties of the materials under investigation. In previous work, a number of different two-electrode geometries have been used including cylindrical Couette [26,27,31], plate-plate [28,39,43,45], ring geometries [29,30,37,38] and pipe flow [32]. The difficulty inherent in performing simultaneous rheo-electric measurements lies in the additional friction caused by the electrical connection to the rotating electrode (typically through a slip ring), which can induce large errors in the measurement of the torque, when measured at the same electrode.…”

Section: Rheo-electric Test Fixturementioning

confidence: 99%

“…conductivity σ, permittivity ), which coupled with standard rheological measurements also provides additional information on the evolution of the fluid microstructure under flow [26][27][28][29][30][31][32]. Previous rheoelectric studies have focused mostly on dielectric complex fluids such as polymeric materials [33][34][35], liquid crystals [28], colloidal suspensions [32] and electrorheological fluids [36], as well as weakly conductive materials (σ 1 mS/cm) such as CNT nanocomposites [29,30,[37][38][39][40][41] and weakly conductive carbon black gels [26,27,[42][43][44][45]. Typical commercial rheo-electric platforms involve the use of a rheometer coupled with an electrical measuring system such as an LCR meter that measures electric or dielectric constants simultaneously.…”

Section: Introductionmentioning

confidence: 99%

“…Another microstructural probe, less frequently employed, is measurement of the electrical properties of * ahelal@mit.edu the fluid (e.g. conductivity σ, permittivity ), which coupled with standard rheological measurements also provides additional information on the evolution of the fluid microstructure under flow [26][27][28][29][30][31][32]. Previous rheoelectric studies have focused mostly on dielectric complex fluids such as polymeric materials [33][34][35], liquid crystals [28], colloidal suspensions [32] and electrorheological fluids [36], as well as weakly conductive materials (σ 1 mS/cm) such as CNT nanocomposites [29,30,[37][38][39][40][41] and weakly conductive carbon black gels [26,27,[42][43][44][45].…”

Section: Introductionmentioning

confidence: 99%

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Simultaneous Rheoelectric Measurements of Strongly Conductive Complex Fluids

Helal¹,

Divoux²,

McKinley³

2016

Phys. Rev. Applied

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We introduce an modular fixture designed for stress-controlled rheometers to perform simultaneous rheological and electrical measurements on strongly conductive complex fluids under shear. By means of a nontoxic liquid metal at room temperature, the electrical connection to the rotating shaft is completed with minimal additional mechanical friction, allowing for simultaneous stress measurements at values as low as 1 Pa. Motivated by applications such as flow batteries, we use the capabilities of this design to perform an extensive set of rheoelectric experiments on gels formulated from attractive carbon-black particles, at concentrations ranging from 4 to 15 wt %. First, experiments on gels at rest prepared with different shear histories show a robust power-law scaling between the elastic modulus G 0 0 and the conductivity σ 0 of the gels-i.e., G 0 0 ∼ σ α 0 , with α ¼ 1.65 AE 0.04, regardless of the gel concentration. Second, we report conductivity measurements performed simultaneously with creep experiments. Changes in conductivity in the early stage of the experiments, also known as the Andrade-creep regime, reveal for the first time that plastic events take place in the bulk, while the shear rate _ γ decreases as a weak power law of time. The subsequent evolution of the conductivity and the shear rate allows us to propose a local yielding scenario that is in agreement with previous velocimetry measurements. Finally, to establish a set of benchmark data, we determine the constitutive rheological and electrical behavior of carbon-black gels. Corrections first introduced for mechanical measurements regarding shear inhomogeneity and wall slip are carefully extended to electrical measurements to accurately distinguish between bulk and surface contributions to the conductivity. As an illustrative example, we examine the constitutive rheoelectric properties of five different grades of carbon-black gels and we demonstrate the relevance of this rheoelectric apparatus as a versatile characterization tool for strongly conductive complex fluids and their applications.

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Section: Rheo-electric Test Fixturementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Simultaneous Rheoelectric Measurements of Strongly Conductive Complex Fluids

Helal¹,

Divoux²,

McKinley³

2016

Phys. Rev. Applied

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“…3). There are also examples for metallic 19 (blocking effect of notches) and colloidal 20 (shear disruption of a conductive network) glasses, and model calculations of hysteresis loops in rugged potential landscapes 21 . The dynamics of shear-related interfacial effects have also been studied 22 in electrorheological fluids, which are suspensions of particles having higher dielectric constant or electric conductivity than that of suspending fluids with a low viscosity (similar to Si nc embedded in SiO x glass films).…”

Section: Snw Formationmentioning

confidence: 99%

Internal stresses and formation of switchable nanowires at thin silica film edges

Phillips

2011

Journal of Applied Physics

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At vertical edges, thin films of silicon oxide (SiO2−x) can contain defect-free semiconductive c-Si layered nanocrystals (Si NC) embedded in and supported by an insulating g-SiO2 matrix. Yaoet al. [Appl. Phys. A (in press)] have shown that a trenched thin film geometry enables the NC to form switchable nanowires (SNW) when trained by an applied field. The field required to form SNW decreases rapidly within a few cycles, or by annealing at 600 °C in even fewer cycles, and is stable to 700 °C. Here we describe the intrinsic evolution of Si NC and SNW in terms of the competition between internal stresses and electro-osmosis. The analysis relies heavily on experimental data from a wide range of thin film studies, and it explains why a vertical edge across the planar polySi-SiO2−x interface is necessary to form SNW. The discussion also shows that the formation mechanisms of Si NC and polySi/SiO2−x SNW are intrinsic and result from optimization of nanowire connectivity in the presence of residual host misfit stresses.

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“…Water contact angles have been reported for PANI in the literature only rarely 5–7. This parameter is of importance, for example, for the performance of electrorheological fluids4, along with the conductivity of particles constituting the electrorheological suspension 8. The wettability of PANI can also be modulated by electrochemical switching among the leucoemeraldine, emeraldine and pernigraniline states 9.…”

Section: Introductionmentioning

confidence: 99%

Control of polyaniline conductivity and contact angles by partial protonation

Blinova

Stejskal

Trchová

et al. 2007

Polymer International

124

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Many studies require a specific value of conductivity when investigating conducting polymers. The conductivity of polyaniline can efficiently be controlled by partial protonation of the polyaniline base. Although this is a simple task in principle, practical guidelines are missing. In the present study, the changes in the conductivity of polyaniline base after immersion in aqueous solutions of various acids are reported. Polyaniline base has been reprotonated in aqueous solutions of picric, camphorsulfonic and phosphoric acids. The conductivity of partially reprotonated polyaniline varied between 10 −9 and 10 0 S cm −1 . The relation between the pH of a phosphoric acid solution, which was in equilibrium with polyaniline, and the conductivity σ is pH = 0.77 − 0.64 log(σ [S cm −1 ]). The wettability, i.e. water contact angles, can similarly be set by partial protonation to between 78 • for polyaniline base and 44 • for polyaniline reprotonated in 1 mol L −1 phosphoric acid. In solutions of picric acid, the transition from the non-conducting to the conducting state occurs over a narrow range of acid concentrations, and the tuning of conductivity is consequently difficult. Phosphoric acid is well suited for the control of conductivity of polyaniline because of the moderate dependence of the conductivity on the acid concentration or pH.

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Shear-induced changes of electrical conductivity in suspensions

Cited by 7 publications

References 50 publications

Simultaneous Rheoelectric Measurements of Strongly Conductive Complex Fluids

Simultaneous Rheoelectric Measurements of Strongly Conductive Complex Fluids

Internal stresses and formation of switchable nanowires at thin silica film edges

Control of polyaniline conductivity and contact angles by partial protonation

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