Depinning and heterogeneous dynamics of colloidal crystal layers under shear flow

Abstract

Using Brownian dynamics (BD) simulations and an analytical approach we investigate the shearinduced, nonequilibrium dynamics of dense colloidal suspensions confined to a narrow slit-pore. Focusing on situations where the colloids arrange in well-defined layers with solidlike in-plane structure, the confined films display complex, nonlinear behavior such as collective depinning and local transport via density excitations. These phenomena are reminiscent of colloidal monolayers driven over a periodic substrate potential. In order to deepen this connection, we present an effective model which maps the dynamics of the shear-driven colloidal layers to the motion of a single particle driven over an effective substrate potential. This model allows to estimate the critical shear rate of the depinning transition based on the equilibrium configuration, revealing the impact of important parameters such as the slit-pore width and the interaction strength. We then turn to heterogeneous systems where a layer of small colloids is sheared with respect to bottom layers of large particles. For these incommensurate systems we find that the particle transport is dominated by density excitations resembling the so-called "kink" solutions of the Frenkel-Kontorova (FK) model. In contrast to the FK model, however, the corresponding "antikinks" do not move.

Shear-induced laning transition in a confined colloidal film

“…The present investigation extends earlier numerical and theoretical studies by some of us where we focused on shear-induced transitions in bilayer systems [27,28] and, in particular, their description within the FrenkelKontorova model for solid friction [29]. From the perspective of a shear-driven bilayer, the trilayer film can be seen as a first step towards the third dimension.…”

Laning, thinning and thickening of sheared colloids in a two-dimensional Taylor–Couette geometry

“…Recent experiments with optically confined microspheres have addressed the pressure exerted to the boundary 23 and the transmission of torque from the boundary to the center, 24 while the rich and complex rheological properties of these systems remain unexplored. In addition, the interplay between shear and confinement gives rise to a host of new phenomena including buckling instabilities, transport via density waves, heterogeneities and defects that have been explored in the past theoretically 21,[25][26][27] and experimentally on 2D [28][29][30] and 3D colloidal systems. [31][32][33] In this article we investigate the dynamics and deformations of a circular colloidal cluster composed by interacting microspheres that are assembled and sheared via two independent driving fields.…”

Substrate induced freezing, melting and depinning transitions in two-dimensional liquid crystalline systems

“…22,23 Studies with such substrates reveal a variety of phenomena like a commensurate–incommensurate phase transition, 24–27 pinning-depinning transitions. 28–31 There are a wide variety of particle-like systems coupled with the underlying substrate exhibit depinning transition with the external driving forces. 32,33 These include colloids, Wigner crystals, and dusty plasmas.…”