Connecting structure, dynamics and viscosity in sheared soft colloidal liquids: a medley of anisotropic fluctuations

Abstract

Structural distortion and relaxation are central to any liquid flow. Their full understanding requires simultaneous probing of the mechanical as well as structural and dynamical response. We provide the first full dynamical measurement of the transient structure using combined coherent X-ray scattering and rheology on electrostatically interacting colloidal fluids. We find a stress overshoot during the start-up of shear which is due to the strong anisotropic overstretching and compression of nearest-neighbor distances. The rheological response is reflected in uncorrelated entropy-driven intensity fluctuations.While the structural distortion under steady shear is well described by Smoluchowski theory, we find an increase of the particle dynamics beyond the trivial contribution of flow. After the cessation of shear, the full fluid microstructure and dynamics are restored, both on the structural relaxation timescale. We thus find unique structure-dynamics relations in liquid flow, responsible for the macroscopic rheological behavior of the system.

Nonequilibrium free energy of colloidal glasses under shear

“…The suspension is loaded in a cell between two horizontal, parallel plates 65 µm apart. A piezoelectric translation stage moves the top plate, applying shear at very slow rates betweenγ = 1.5×10 −5 s −1 and 2.8 × 10 −4 s −1 , of the order of the inverse relaxation time; these shear rates are significantly smaller than in other studies on colloidal flows [10][11][12][13]. The plates are immersed in a colloidal reservoir; hence the sheared suspension can dilate under constant osmotic pressure.…”

Polymer Crystallization Studied by Hyphenated Rheology Techniques: Rheo‐NMR, Rheo‐SAXS, and Rheo‐Microscopy

“…who developed a hyphenated set‐up based on a stress‐controlled rheometer with a vertical beam path for the study of low to highly viscous samples (Figure c). The latter set‐up was used in the experiments presented here, and furthermore by other researchers to study block copolymers, platelet dispersions, and colloidal systems . Recently, hyphenations of extensional rheometers and X‐ray scattering techniques were used by Yan et al., Liu et al., and Wingstrand et al .…”

Brownian and advective dynamics in microflow studied by coherent X-ray scattering experiments

“…X-rays can probe a large range of momentum transfers q and have a large penetration depth, which allows for probing a wide range of length scales and to analyze samples which are optically opaque (Leheny, 2012;Shpyrko, 2014). XPCS has been used for studying the dynamics of colloidal (Dierker et al, 1995;Burghardt et al, 2012;Westermeier et al, 2016), polymeric (Falus et al, 2005) and soft hybrid systems (Carnis et al, 2014;Herná ndez et al, 2015). Pioneering experiments on XPCS in flowing liquid samples have been performed by Fluerasu et al (Fluerasu et al, , 2010Busch et al, 2008), studying the laminar flow in tube-like flow cells.…”