Dynamics of dilute colloidal suspensions in modulated potentials

Abstract

T he dynamics of dilute suspensions of charged polyslyrene sphercs have heen studied in a sinusoidal potential. Wc invcstigated experimclllally and theoretically (he elreel of the wavelength and amplitude of this potential as weil as the partieIe sizc on the mcnn square displacemenl, the distribution of displacemeuls and the non··Gaussian parameter. These propcl'ties seale with thc radius of the particles and the magnitude of the waveveetor 01' the potential as expected frorn a dimensional analysis. In contrast, they show a non-trivial dependel\ce on the amplitude of tJle potential, which determines the barrier height encoul\tei"ed in long-distance motiolls and also the intermediate-time dynamics in the potential weil. The periodic potential leads to particle dynamies which resemble the self dynamics of variolls systems approaching their glass transition. In pnrticular, we found thaI the timc-dependent mean sq uare displacements detennined in ollr system are surprisingly close to the ones in a quasi twodimensional colloidal supercooled liquid . In this case, the role of Ihe colloid volUlnc fraction is played by the amplitude of the potential. The similat"ity of the menn sq uare di splacements is partieularly striking sinee an individual eolloidlll particle in a periodic potential represen ts a considerably simpler si tuation than a highly concentrated multi-particle sys tem .

Delay-induced transport in a rocking ratchet under feedback control

“…In fact, similar values are found in experiments of colloids in structured light fields [10,41,42]. Time is measured in units of the Brownian timescale, τ = σ 2 /D 0 , which is of the order of 10 0 s to 10 2 s for typical colloids [10,[41][42][43][44]. In all calculations, the initial condition for the probability density is a δ-function localized at the minimum of V (z), z min = 0.…”

“…To judge the impact on transport properties such as J, these experimental data for τ D have to be compared with the intrinsic ("Brownian") time scale τ = σ 2 /D 0 of a colloidal system. The latter time is about 1s τ 100s (for particle sizes of 1µm σ 10µm and diffusion constants D 0 ≈ 10 −13 m 2 /s for colloids in an aqueous solution [10,[41][42][43][44]); therefore, one typically has τ > τ D . According to the results presented in Fig.…”

Minimal model for short-time diffusion in periodic potentials

“…The transport of particles in modulated potentials plays a fundamental role in diverse fields such as colloidal particles on topologically or energetically structured surfaces [1,2], particles in optical lattices [3] and optical line traps [4], biased Josephson junctions [5], and in biophysical processes [6,7]. In many of these cases, the dynamics can be described as overdamped (i.e., noninertial) Brownian motion in one spatial direction.…”

Novel structure formation of a phase separating colloidal fluid in a ratchet potential

“…-Understanding the dynamics of particles in complex geometry is an ubiquitary problem throughout non-equilibrium statistical physics with applications in diverse fields such as biology, condensed matter and nanotechnology [1,2]. Paradigm examples are colloidal particles in periodic optical (or otherwise modulated) potentials [3][4][5], which display a variety of fascinating transport phenomena including giant diffusion [6], subdiffusive motion [7], and ratchet effects, i.e., fluctuatinginduced transport in the absence of a biasing deterministic force [8]. Indeed, ratchet-driven transport of Brownian (overdamped) particles has been studied in a variety of optical [9,10], magnetic [11][12][13][14][15][16], and biological systems [17][18][19].…”