Confocal microscopy of colloidal dispersions in shear flow using a counter-rotating cone–plate shear cell

Abstract

We report on novel possibilities for studying colloidal suspensions in a steady shear field in real space. Fluorescence confocal microscopy is combined with the use of a counter-rotating cone-plate shear cell. This allows imaging of individual particles in the bulk of a sheared suspension in a stationary plane. Moreover, this plane of zero velocity can be moved in the velocity gradient direction while keeping the shear rate constant. The colloidal system under study consists of rhodamine labelled PMMA spheres in a nearly density and refractive index matched mixture of cyclohexylbromide and cis-decalin. We show measured flow profiles in both the fluid and the crystalline phase and find indications for shear banding in the case of a sheared crystal. Furthermore, we show that, thanks to the counter-rotating principle of the cone-plate shear cell, a layer of particles in the bulk of a sheared crystalline suspension can be imaged for a prolonged time, with the result that their positions can be tracked.

Dynamic yield stresses of glasses: asymptotic formulae

“…In the latter context, considering the higher order corrections − f c ∝G + εγG (2) + · · ·, one recognizes that each orderG (i) possesses a long time expansion like equation (A.1),…”

A multi-axis confocal rheoscope for studying shear flow of structured fluids

“…Independently rotating both surfaces, while more difficult, allows the zero-velocity plane to be moved away from the sample boundaries. 32,35 This, in turn, allows particle tracking in bulk, even under very rapid shear conditions. An alternate approach for torsional flows requires mounting a commercial rheometer on a confocal microscope.…”

“…Using this technique, individual structures of interest can be followed in real time or, by scanning through the sample, the full three-dimensional (3D) structure can be mapped out, allowing for accurate reconstruction of flow profiles using particle velocimetry and detailed measurements of a material's dynamic microstructure. [29][30][31][32][33][34] Two types of experimental designs combining confocal microscopy with precise flow control have been reported. The major distinction between these two types is the geometry of the flow.…”

“…The first group of designs uses counter-rotating surfaces to drive torsional flows with circular streamlines. 25,30,32,[35][36][37][38] Often, one of these surfaces is fixed in the laboratory frame. Independently rotating both surfaces, while more difficult, allows the zero-velocity plane to be moved away from the sample boundaries.…”

Experimental observation of the crystallization of hard-sphere colloidal particles by sedimentation onto flat and patterned surfaces

“…[7][8][9] A particularly exciting development is the use of monodisperse hard sphere colloids to simulate structural dynamics in dense atomic or molecular systems, [10] phenomena that are experimentally inaccessible on the atomic scale. Examples include homogeneous and heterogeneous nucleation of crystals, [11,12] crystal-fluid interfaces, [13] glass formation, [14,15] matter under shear [16,17] or thermal capillary waves. [18] Hard sphere crystals are excellent models for simple metals.…”