Particle sizing for flowing colloidal suspensions using flow-differential dynamic microscopy

Abstract

Particle size is a key variable in understanding the behaviour of the particulate products that underpin much of our modern lives. Typically obtained from suspensions at rest, measuring the particle...

Characterising shear-induced dynamics in flowing complex fluids using differential dynamic microscopy

“…In steady flows, particles are subject to diffusive dynamics and to advection across the field of view with a fixed velocity, v. To characterise the nonaffine motion of the particles, we must effectively reduce the impact of the affine motion due to the advective flow. This is obtained using flow-DDM, 19 which we have introduced elsewhere and we present only a brief summary. Crucially, flow-DDM performs DDM analysis in the co-moving frame by calculating the flow-corrected DICF, % g, gðq; tÞ ¼Ĩðq; t þ tÞe ÀiqÁṽt ÀĨðq;…”

“…Eqn ( 6) requires knowledge of v, which we measure using j-DM, 26 a Fourier-space method that can be efficiently combined with DDM. 19 To further minimise the impact of flow, we calculate % g > by averaging % g over a narrow range of q in a sector perpendicular to the flow direction [AEy = 31, Fig. 1(a)].…”

“…Soft Matter sectioning 19 and diffusivity has been measured with multiple methods. 17,45,46 Secondly, particle resolution is not needed and with this comes a large field of view that allows rapid data acquisition suitable for a high-throughput technique 20 and information on multiple lengthscales.…”

“…To characterise the non-affine motion of the particles, we must effectively reduce the impact of the affine motion due to the advective flow. This is obtained using flow-DDM, 19 which we have introduced elsewhere and we present only a brief summary. Crucially, flow-DDM performs DDM analysis in the co-moving frame by calculating the flow-corrected DICF, ḡ , Eqn (6) requires knowledge of v⃑ , which we measure using φ -DM, 26 a Fourier-space method that can be efficiently combined with DDM.…”

“…We verify echo-DDM using a dilute colloidal suspension and then explore its potential using a silicone-oil emulsion imaged with rheo-confocal microscopy. 18 Using a combination of echo-DDM and flow-DDM, 19 we investigate both oscillatory and steady shear, respectively, to fully characterise yielding of such a flowing complex fluid. This allows a comparison of the microscopic and bulk behaviour under both steady and oscillatory shear flows, which reveal a comprehensive view of the yielding process.…”