scholarly journals Diffusiophoresis of Concentrated Suspensions of Spherical Particles with Distinct Ionic Diffusion Velocities

2007 ◽  
Vol 111 (10) ◽  
pp. 2533-2539 ◽  
Author(s):  
Jyh-Ping Hsu ◽  
James Lou ◽  
Yan-Ying He ◽  
Eric Lee
Keyword(s):  
Spherical Particles ◽  
Ionic Diffusion ◽  
Concentrated Suspensions

Suspensions with a tunable effective viscosity: a numerical study

2012 ◽  
Vol 693 ◽  
pp. 345-366 ◽  
Author(s):  
L. Jibuti ◽  
S. Rafaï ◽  
P. Peyla
Keyword(s):  
Effective Viscosity ◽  
Volume Fraction ◽  
Numerical Study ◽  
Spherical Particles ◽  
Dimensionless Number ◽  
Particle Rotation ◽  
Concentrated Suspensions ◽  
Sheared Suspensions ◽  
Neutrally Buoyant ◽  
Universal Behaviour

AbstractIn this paper, we conduct a numerical investigation of sheared suspensions of non-colloidal spherical particles on which a torque is applied. Particles are mono-dispersed and neutrally buoyant. Since the torque modifies particle rotation, we show that it can indeed strongly change the effective viscosity of semi-dilute or even more concentrated suspensions. We perform our calculations up to a volume fraction of 28 %. And we compare our results to data obtained at 40 % by Yeo and Maxey (Phys. Rev. E, vol. 81, 2010, p. 62501) with a totally different numerical method. Depending on the torque orientation, one can increase (decrease) the rotation of the particles. This results in a strong enhancement (reduction) of the effective shear viscosity of the suspension. We construct a dimensionless number $\Theta $ which represents the average relative angular velocity of the particles divided by the vorticity of the fluid generated by the shear flow. We show that the contribution of the particles to the effective viscosity can be suppressed for a given and unique value of $\Theta $ independently of the volume fraction. In addition, we obtain a universal behaviour (i.e. independent of the volume fraction) when we plot the relative effective viscosity divided by the relative effective viscosity without torque as a function of $\Theta $. Finally, we show that a modified Faxén law can be equivalently established for large concentrations.

Large-Scale Self-Assembly in Weakly-Flocculated Suspensions

2019 ◽  
Vol 4 (1) ◽  
pp. 68-74
Author(s):  
Aleš Dakskobler ◽  
Matjaz Valant
Keyword(s):  
Self Assembly ◽  
Shear Force ◽  
Large Scale ◽  
Hard Spheres ◽  
Colloidal Crystals ◽  
The Self ◽  
Spherical Particles ◽  
Particle Interactions ◽  
Concentrated Suspensions ◽  
Average Angle

Background: Studies on the formation of colloidal crystals in concentrated suspensions have mainly been based on dispersed suspensions with a repulsive inter-particle potential of hard or nearly hard spheres. The self-assembly in weakly-flocculated suspensions has still been unrealized. Here, we report on the formation of ordered structures in concentrated suspensions of nearly-hard spherical particles with weakly-attractive inter-particle interactions that are an order of magnitude higher than the particles’ thermal energy. Methods: In our case, the self-assembly in such suspensions is not thermodynamically driven, but an external shear force must be applied. The driving force for the particles’ ordering is an increase in the inter-particle interactions. This manifests itself in a decrease in the average angle between the interparticle interaction direction and the applied shear stress direction. Results: For a successful ordering into a large-scale closed packed assembly, the external shear force must not exceed the inter-particle attractive interaction for the minimum possible average angle (as in the closed packed structures) but be high enough to enable the particles to move in the highly loaded suspension. Conclusion: The developed method for the self-assembly of the weakly flocculated systems can be applied very generally e.g. a control over a composition of heterogeneous colloidal crystals, manufacturing of the large-scale photonic crystals or preparation of very densely packed compacts of particles needed for the production of sintered ceramics.

scholarly journals Dipolophoresis in concentrated suspensions of ideally polarizable spheres

2019 ◽  
Vol 875 ◽  
Author(s):  
Siamak Mirfendereski ◽  
Jae Sung Park
Keyword(s):  
Large Scale ◽  
Volume Fraction ◽  
Local Maximum ◽  
Close Packing ◽  
Density Fluctuations ◽  
Distribution Functions ◽  
Spherical Particles ◽  
Concentrated Suspensions ◽  
Induced Charge ◽  
Pair Distribution Functions

The dynamics of ideally polarizable spherical particles in concentrated suspensions under the effects of nonlinear electrokinetic phenomena is analysed using large-scale numerical simulations. Particles are assumed to carry no net charge and considered to undergo the combination of dielectrophoresis and induced-charge electrophoresis termed dipolophoresis. Chaotic motion and resulting hydrodynamic diffusion are known to be driven by the induced-charge electrophoresis, which dominates the dielectrophoresis. Up to a volume fraction $\unicode[STIX]{x1D719}\approx 35\,\%$, the particle dynamics seems to be hindered by the increase in the magnitude of excluded volume interactions with concentration. However, a non-trivial suspension behaviour is observed in concentrated regimes, where the hydrodynamic diffusivity starts to increase with the volume fraction at $\unicode[STIX]{x1D719}\approx 35\,\%$, before reaching a local maximum, and then drastically decreases on approaching random close packing. Similar non-trivial behaviours are observed in the particle velocity and number-density fluctuations around volume fractions at which the non-trivial behaviour of the hydrodynamic diffusion is observed. We explain these non-trivial behaviours as a consequence of particle contacts, which are related to the dominant mechanism of particle pairings. The particle contacts are classified into attractive and repulsive classes by the nature of contacts, and in particular, the strong repulsive contact becomes predominant at $\unicode[STIX]{x1D719}>20\,\%$. Moreover, this transition is visible in the pair distribution functions, which also reveal the change in the suspension microstructure in concentrated regimes. It appears that strong and massive repulsive contacts along the direction perpendicular to an electric field promote the non-trivial suspension behaviours observed in concentrated regimes.

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