Superadiabatic demixing in nonequilibrium colloids

Abstract

Dispersed colloidal particles that are set into systematic motion by a controlled external field constitute excellent model systems for studying structure formation far from equilibrium. Here we identify a unique demixing force that arises from repulsive interparticle interactions in driven binary colloids. The corresponding demixing force density is resolved in space and in time and it counteracts diffusive currents which arise due to gradients of the local mixing entropy. We construct a power functional approximation for overdamped Brownian dynamics that describes superadiabatic demixing as an antagonist to adiabatic mixing as originates from the free energy. We apply the theory to colloidal lane formation. The theoretical results are in excellent agreement with our Brownian dynamics computer simulation results for adiabatic, structural, drag and viscous forces. Superadiabatic demixing allows to rationalize the emergence of mixed, laned and jammed states in the system.

Phase Transitions of Oppositely Charged Colloidal Particles Driven by Alternating Current Electric Field

“…In this context, it is relevant to note that Schmidt and co-workers have suggested that lane formation can be understood in terms of so-called superadiabatic forces, generated by the dynamics of a driven fluid. 49 , 50 …”

Shear-induced deconfinement of hard disks

“…The adiabatic construction was used to identify these superadiabatic force contributions. The concept of superadiabatic forces [31,32,44] allows systematic classification [42] of flow and structural effects, including viscous [39][40][41] and structural [41][42][43] force contributions. Future work could be directed at the behavior at low shear rates.…”

“…Functional integration methods were developed [38], and the relevance of local particle number conservation was demonstrated [56,57]. Expressing the superadiabatic free power functional via the velocity gradient [39][40][41][42][43] has facilitated the description of viscous [39,40,42] and of structural superadiabatic force contributions [41][42][43]. Superadiabatic forces are accessible in many-body simulations [32,44,45].…”

Power functional theory for Newtonian many-body dynamics

“…Experimental systems of magnetic colloids that are placed above suitably patterned substrates offer much sophisticated control of driving protocols (Loehr et al, 2016(Loehr et al, , 2018. Geigenfeind et al (2020) have analyzed the forces that occur in the Brownian dynamics of a generic twodimensional binary repulsive sphere model. They recast the internal force density for binary mixtures (as laid out in Sec.…”

“…The dynamical DFT can be viewed as being based on the approximation that the nonequilibrium dynamics are represented as a sequence of "adiabatic states" that each are taken to be in equilibrium. While the adiabatic approximation for dynamical processes can be valid in certain cases, important physical effects are absent (Fortini et al, 2014), such as drag forces (Krinninger et al, 2016), viscosity (de las Heras and Schmidt, 2018), and structural nonequilibrium forces (de las Heras and Geigenfeind et al, 2020;Stuhlmüller et al, 2018;.…”