Colloidal binary mixtures at fluid-fluid interfaces under steady shear: structural, dynamical and mechanical response.
We experimentally study the link between structure, dynamics and mechanical response of two-dimensional (2D) binary mixtures of colloidal microparticles spread at water/oil interfaces. The particles are driven into steady shear by a microdisk forced to rotate at a controlled angular velocity. The flow causes particles to layer into alternating concentric rings of small and big colloids. The formation of such layers is linked to the local, position-dependent shear rate, which triggers two distinct dynamical regimes: particles either move continuously ("Flowing") close to the microdisk, or exhibit intermittent "Hopping" between local energy minima farther away. The shear-rate-dependent surface viscosity of the monolayers can be extracted from a local interfacial stress balance, giving "macroscopic" flow curves whose behavior corresponds to the distinct microscopic regimes of particle motion. Hopping regions reveal a higher resistance to flow compared to the flowing regions, where spatial organization into layers reduces dissipation.
Laboratory for Interfaces, Soft matter and Assembly, Department of Materials, ETH Zurich, Switzerland. ivo.buttinoni@mat.ethz.ch.
Ivo
I
Buttinoni
Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, California 93106-5080, USA.
Zachary A
ZA
Zell
Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, California 93106-5080, USA.
Todd M
TM
Squires
Laboratory for Interfaces, Soft matter and Assembly, Department of Materials, ETH Zurich, Switzerland. ivo.buttinoni@mat.ethz.ch.
Lucio
L
Isa
D003102:Colloids / Q000737:chemistry*; D009038:Motion; D012212:Rheology; D013499:Surface Properties; D014783:Viscosity
D003102:Colloids