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Issue 10, 2020
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Viscoelastic cluster densification in sheared colloidal gels

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Many biological materials, consumer products and industrial formulations are colloidal suspensions where the suspending medium is itself a complex fluid, and such suspensions are effectively soft matter composites. At rest, the distortion of the microstructure in the suspending fluid by the particles leads to attractive interactions between them. During flow, the presence of a microstructure in the viscoelastic suspending medium changes the hydrodynamic forces due to the non-Newtonian and viscoelastic effects. However, little is known about the structural development, the rheology and the final properties of such materials. In the present study, a model flocculated suspension in both a Newtonian and a viscoelastic medium was studied by combined rheological and rheo-confocal methods. To this extent, micrometer-sized fluorescent PMMA particles were dispersed in polymeric matrices (PDMS). The effect of fluid viscoelasticity is studied by comparing the results for a linear and a branched polymer. Stress jump experiments on the suspensions were used to de-convolute the rate dependence of the viscous and elastic stress contributions in both systems. These results were compared to a qualitative and quantitative analysis of the microstructure during flow as studied by fast structured illumination confocal microscopy, using a counter-rotating rheometer. At comparable interaction strength, as quantified by equal Bingham numbers, the presence of medium viscoelasticity leads to an enhanced densification of the aggregates during steady-state flow, which is reflected in lower limiting high shear viscosities. Following a strong preshear, the structural and mechanical recovery is also altered between the Newtonian and viscoelastic matrix with an increase in the percolation threshold, but with the potential to build stronger materials exploiting the combination of processing history and medium rheology at higher volume fractions.

Graphical abstract: Viscoelastic cluster densification in sheared colloidal gels

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Supplementary files

Article information

02 Dec 2019
29 Jan 2020
First published
29 Jan 2020

This article is Open Access

Soft Matter, 2020,16, 2437-2447
Article type

Viscoelastic cluster densification in sheared colloidal gels

R. Massaro, G. Colombo, P. Van Puyvelde and J. Vermant, Soft Matter, 2020, 16, 2437
DOI: 10.1039/C9SM02368B

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