Laning, Thinning and Thickening of Sheared Colloids in a Two-dimensional Taylor-Couette Geometry

TL;DR

This study explores how sheared 2D colloidal clusters exhibit structural changes like thinning and thickening under different driving forces, combining experiments and simulations to understand microscopic rheological behavior.

Contribution

It introduces a novel experimental setup using magnetic and optical torques to control and analyze colloidal dynamics in a 2D Taylor-Couette system, supported by Brownian dynamics simulations.

Findings

Continuous thinning of particle layers under shear

Thickening of the third layer above a threshold field

Microscopic insights into shear-induced structural changes

Abstract

We investigate the dynamics and rheological properties of a circular colloidal cluster that is continuously sheared by magnetic and optical torques in a two-dimensional (2D) Taylor-Couette geometry. By varying the two driving fields, we obtain the system flow diagram and report the velocity profiles along the colloidal structure. We then use the inner magnetic trimer as a microrheometer, and observe continuous thinning of all particle layers followed by thickening of the third one above a threshold field. Experimental data are supported by Brownian dynamics simulations. Our approach gives a unique microscopic view on how the structure of strongly confined colloidal matter weakens or strengthens upon shear, envisioning the engineering of rheological devices at the microscales.