Abstract
Nonaqueous layered silicate suspensions have a complex rheological behavior due to the presence of a microstructure on multiple length scales, which is sensitive to flow and flow history. In the present work, the flow-induced orientation and anisotropy of the nonequilibrium metastable structures in nonaqueous layered silicate suspensions has been studied using a combination of light scattering, scattering dichroism, and advanced rheometric measurements, including two dimensional small amplitude oscillatory shear (2D-SAOS) flow experiments. The nature of the structures during flow was mainly studied by means of small angle light scattering patterns. Linear dichroism measurements in the vorticity and velocity gradient directions were used to assess the microstructural anisotropy. The changes observed in the vorticity plane developed in the same range of shear rate as the shear-thinning behavior of the suspensions. Scattering dichroism was used to demonstrate that the flow-induced anisotropy was locked in up...
Highlights
Colloidal suspensions exhibit a wide range of complex rheological properties including transition from fluidlike to solidlike behavior leading to nonlinear rheological properties and thixotropic phenomenaBarnes1997͒; Mewis1979͔͒
As the length scales probed in the SALS experiments are much larger than the particle size, the power-law decay of the scattered intensity, I, with the scattering vector, q, suggests that the microstructure is self-similar in nature, in agreement with previous measurements on similar systemsSchaefer et al ͑1984͒; Pignon et al ͑1997a
A slight anisotropy appears, with two apparent lobes in the scattering patterns running along the flow direction
Summary
Colloidal suspensions exhibit a wide range of complex rheological properties including transition from fluidlike to solidlike behavior leading to nonlinear rheological properties and thixotropic phenomenaBarnes1997͒; Mewis1979͔͒ This behavior stems from the self-organization of the colloidal particles on multiple length scalesHoekstra et al ͑2005͒; Pignon et al ͑1997a͒. Layered silicates of the smectite group, commonly used as rheological modifiers in paints, ceramic additives, inks, drilling fluids, and greases, have attracted a great interest in the emerging field of polymer nanocompositesPatel et al ͑2006͔͒. Their ordering at the nanometer length scale leads to unique mechanical, electrical, optical, and thermal propertiesRay and Okamoto2003͔͒. The discussion focuses on results pertaining to suspensions of attractive particles
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