Shear viscosity and structural scalings in model adhesive hard-sphere gels

Abstract

We present experiments and simulations that show a fundamental scaling for both the rheology and microstructure of flowing gels. Unique flow-SANS measurements demonstrate that the structure orients along both the neutral and compression axis. We quantify the anisotropy using a single parameter, α, that scales by a dimensionless number, M^{'}, that arises from a force balance on a particle. Simulations support the scalings and confirm the results are independent of the shape and range of the potential suggesting a universal for colloidal gels with short-ranged attractions.

Superposition rheology and anisotropy in rheological properties of sheared colloidal gels

“…The scaling, therefore, holds (at least approximately) not only for more homogeneous systems such as the thermoreversible gels studied by Wagner and coworkers [17,49] but also for the present, more heterogeneous colloidal gel. Therefore, the emerging picture is that the aggregates gradually evolve and decrease in size during more intense shearing, as a result of the interplay between the shear forces breaking them up and the maximum attractive interparticle force.…”

“…The Bingham number compares the hydrodynamic stresses to the structural stresses, which are due to the attractive interactions, through the yield stress. The latter is proportional to the maximal attractive interparticle force, i.e., the maximum slope of the pair potential U: r y $ / 2 =a 2 ðdU=drÞ [49,50]. This scaling proved successful for the steady shear rheology of thermoreversible octadecyl silica gels [17].…”

Echoes in x-ray speckles track nanometer-scale plastic events in colloidal gels under shear

“…We note that the brief interruptions at the strain extrema for obtaining the x-ray images potentially complicate comparisons of the echo results with rheology and (incoherent) scattering studies that employ large-amplitude oscillatory shear (LAOS) to investigate the nonlinear response of colloidal gels [12][13][14]22,28]. However, we believe these complications are minor and valid comparisons can be made.…”

“…Conventional small-angle x-ray and neutron scattering under in situ shear has provided information about the average structural modifications of soft materials due to stress and flow [5][6][7][8][9][10][11][12][13][14][15][16]. However, a full understanding of the interdependence of microscopic properties and macroscopic rheology requires in situ information about the structural dynamics driven by stress.…”

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

“…al. showed similar anisotropic scattering in colloidal gels in Newtonian fluids that are aggregated at rest, where the shear stress was found to scale with the degree of anisotropy of particle clusters [40]. However, since our fluids are not significantly aggregated, and do not possess a yield stress, it is impossible to directly compare the results.…”