Imaging the Microscopic Structure of Shear Thinning and Thickening Colloidal Suspensions

Cheng, Xiang; McCoy, Jonathan H.; Israelachvili, Jacob N.; Cohen, Itai

doi:10.1126/science.1207032

Cited by 462 publications

(426 citation statements)

References 36 publications

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“…2D). Furthermore, inside each sample, particles in the x-z layers nearer to the boundary plates-where layering order is strongest (6,26) -show an enhanced string structure as indicated by the higher peak at π∕2 (Fig. 2E).…”

Section: Resultsmentioning

confidence: 99%

“…A further detailed description of our experimental apparatus can be found in ref. 6, and a detailed description of our confocal imaging techniques can be found in the SI Text.…”

Section: Methodsmentioning

confidence: 99%

“…Once driven out of equilibrium, a material can exhibit richer phases with many unexpected structures (2)(3)(4)(5)(6). However, the dynamics of these nonequilibrium phases are much less understood relative to their equilibrium counterparts (7)(8)(9).…”

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confidence: 99%

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Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow

Cheng

Rice

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Colloidal suspensions self-assemble into equilibrium structures ranging from face-and body-centered cubic crystals to binary ionic crystals, and even kagome lattices. When driven out of equilibrium by hydrodynamic interactions, even more diverse structures can be accessed. However, mechanisms underlying out-of-equilibrium assembly are much less understood, though such processes are clearly relevant in many natural and industrial systems. Even in the simple case of hard-sphere colloidal particles under shear, there are conflicting predictions about whether particles link up into string-like structures along the shear flow direction. Here, using confocal microscopy, we measure the shear-induced suspension structure. Surprisingly, rather than flow-aligned strings, we observe log-rolling strings of particles normal to the plane of shear. By employing Stokesian dynamics simulations, we address the mechanism leading to this out-of-equilibrium structure and show that it emerges from a delicate balance between hydrodynamic and interparticle interactions. These results demonstrate a method for assembling large-scale particle structures using shear flows.colloids | shear-induced structure T he study of ordered structures and symmetries of equilibrium phases in condensed matter is central to our understanding of its various material properties (1). Once driven out of equilibrium, a material can exhibit richer phases with many unexpected structures (2-6). However, the dynamics of these nonequilibrium phases are much less understood relative to their equilibrium counterparts (7-9). Sheared hard-sphere colloidal suspensions provide a simple system for probing many out-of-equilibrium structures. For example, sliding layers in sheared colloidal crystals (10, 11), shear-induced crystallization of colloidal fluids (5), and formation of shear transformation zones-localized regimes of shear-induced structural rearrangement-in colloidal glasses (12) have been observed in such systems.The simplest and lowest ordered structure predicted to arise from sheared hard-sphere colloidal suspensions is a one-dimensional (1D) string structure, where particles link into strings under shear. This structure has received much attention since it was first found in a numerical simulation (13). Despite intensive study (13-23), however, there is still heated debate over whether such a structure exists in experiments (10,23,24) or is an artifact of certain numerical algorithms (20-23). In part, this controversy persists due to the lack of experimental techniques that provide direct visualization of the suspension structure. Since the string structure is predicted to exist in less concentrated suspensions below the crystallization threshold, previous scattering experiments, which average over large sample volumes, have not provided detailed information to unambiguously confirm or disprove the existence of this less regular structure (10,24). Here, by employing fast confocal microscopy, we show that sheared hardsphere colloidal suspensions form strings a...

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Section: Resultsmentioning

confidence: 99%

“…A further detailed description of our experimental apparatus can be found in ref. 6, and a detailed description of our confocal imaging techniques can be found in the SI Text.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow

Cheng

Rice

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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“…This need has driven the development of new optical-rheology platforms with ever increasing sophistication and versatility. [7][8][9][10][11][12][13] Access to time-resolved, three-dimensional information is crucial for an accurate quantification of the microscopic structure that ultimately determines material properties; connecting macroscopic observables, such as shear and bulk moduli, to the relevant physical interactions and structure is a cornerstone of modern materials science.…”

Section: Introductionmentioning

confidence: 99%

Development of a confocal rheometer for soft and biological materials

Dutta

Mbi

Arevalo

et al. 2013

Review of Scientific Instruments

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We discuss the design and operation of a confocal rheometer, formed by integrating an Anton Paar MCR301 stress-controlled rheometer with a Leica SP5 laser scanning confocal microscope. Combining two commercial instruments results in a system which is straightforward to assemble that preserves the performance of each component with virtually no impact on the precision of either device. The instruments are configured so that the microscope can acquire time-resolved, three-dimensional volumes of a sample whose bulk viscoelastic properties are being measured simultaneously. We describe several aspects of the design and, to demonstrate the system's capabilities, present the results of a few common measurements in the study of soft materials.

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“…It is usually attributed to forming and breaking of flow induced microstuctures [30]. Recently, shear thinning was shown to have entropic origins by directly imaging the suspension with fast confocal microscopy [31]. At the moment, it is difficult to point out origins of shear thinning of pure liquids under nanoconfinement.…”

Section: Discussionmentioning

confidence: 99%

The effect of boundary slippage and nonlinear rheological response on flow of nanoconfined water

Sekhon

Ajith

Patil

2017

J. Phys.: Condens. Matter

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Abstract. The flow of water confined to nanometer-sized pores is central to a wide range of subjects from biology to nanofluidic devices. Despite its importance, a clear picture about nanoscale fluid dynamics is yet to emerge. Here we measured dissipation in less than 25 nm thick water films and it was found to decrease for both wetting and non-wetting confining surfaces. The fitting of Carreau-Yasuda model of shear thinning to our measurements implies that flow is non-Newtonian and for wetting surfaces the no-slip boundary condition is largely valid. On the contrary, for non-wetting surfaces boundary slippage occurs with slip lengths of the order of 10 nm. The findings suggest that both, the wettability of the confining surfaces and nonlinear rheological response of water molecules under nano-confinement play a dominant role in transport properties.

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Imaging the Microscopic Structure of Shear Thinning and Thickening Colloidal Suspensions

Cited by 462 publications

References 36 publications

Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow

Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow

Development of a confocal rheometer for soft and biological materials

The effect of boundary slippage and nonlinear rheological response on flow of nanoconfined water

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