Flow-Induced Anisotropic SALS in Silica-Filled PDMS Liquids

Shear-induced clustering of Brownian colloids in associative polymer networks at moderate Péclet number

“…The observed anisotropy indicates shear-induced clustering in the fluid, consistent with previous observations of Brownian suspensions in viscoelastic liquids [7,8]. However, we note that our measurements, which include measurements in all of the orthogonal directions (flow, gradient and vorticity), suggest a clustered microstructure that is qualitatively different than what was inferred from previous studies of scattering in the 1-3 (flow-vorticity) plane alone at smaller qvalues [3,24]. Specifically, those studies hypothesized the formation of chains of particles whose long dimension is oriented along the vorticity axis.…”

“…We note that the q-values associated with the observed anisotropy in the scattering patterns encompasses a range of 0.15 < qa/2π < 0.65, such that we can associate it with pairs or small groups of suspended particles. This is different from previous scattering studies that were performed at much smaller q-values [3,24], and will be important in the interpretation of the data to follow. In the 1-3 (flow-vorticity) plane, the excess scattering is oriented along the flow direction, suggesting that there is an excess of particle pairs along the vorticity direction.…”

“…Also, Haddadi and Morris have shown that, using lattice-Boltmann simulations, pair-sphere trajectories in finite inertia shear flow prefer vorticity alignment [9]. We note that similar clustering has also been observed in systems whose suspension microstructure is aggregated at rest [3], although it is not clear whether the same physics of clustering apply in these systems, or whether the behavior is rather dominated by interparticle attractions. The mechanism of clustering in polymer-colloid mixtures also appears to be different from that observed in highly confined suspensions in Newtonian liquids, which is dominated by hydrodynamic effects of the confining walls.…”

“…Thus, optimizing the final properties of nanocomposites requires careful control of particle dispersion and, therefore, rheology during processing. Since many nanocomposites are processed from solution [3], it is thus critically important to understand the influence of flow on polymer-particle interactions and suspension microstructure of colloidal suspensions in polymer liquids.…”

Small-angle neutron scattering study of shear-induced phase separation in aqueous poly(N-isopropylacrylamide) solutions

“…With PS in DOP a so-called butterfly pattern in SALS and SANS which indicates shear-induced concentration fluctuations is often observed in semi-dilute solutions above the overlap concentration c*. Butterfly scattering patterns have also been observed with polymer networks and some colloidal systems [5][6][7][8][9]. In these complex fluids the viscoelastic properties, especially the first normal stress difference, play an important role for the coupling between density fluctuations and shear stress [10].…”