Anomalous crystalline ordering of particles in a viscoelastic fluid under high shear

Sijie SunNan XueStefano AimeHyoungsoo KimJizhou TangGareth H. McKinleyHoward A. StoneDavid A. Weitz

Sijie SunNan XueStefano Aime ...+4 David A. Weitz

Mar 2023

摘要

Addition of particles to a viscoelastic suspension dramatically alters theproperties of the mixture, particularly when it is sheared or otherwiseprocessed. Shear-induced stretching of the polymers results in elastic stressthat causes a substantial increase in measured viscosity with increasing shear,and an attractive interaction between particles, leading to their chaining. Ateven higher shear rates, the flow becomes unstable, even in the absence ofparticles. This instability makes it very difficult to determine the propertiesof a particle suspension. Here we use a fully immersed parallel plate geometryto measure the high-shear-rate behavior of a suspension of particles in aviscoelastic fluid. We find an unexpected separation of the particles withinthe suspension resulting in the formation of a layer of particles in the centerof the cell. Remarkably, monodisperse particles form a crystalline layer whichdramatically alters the shear instability. By combining measurements of thevelocity field and torque fluctuations, we show that this solid layer disruptsthe flow instability and introduces a new, single-frequency component to thetorque fluctuations that reflects a dominant velocity pattern in the flow.These results highlight the interplay between particles and a suspendingviscoelastic fluid at very high shear rates.

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