Colloidal Motility and Pattern Formation under Rectified Diffusiophoresis

Jérémie Palacci, Benjamin Abécassis, Cécile Cottin-Bizonne, Christophe Ybert, and Lydéric Bocquet

Phys. Rev. Lett. 104, 138302 – Published 1 April 2010

Abstract

In this Letter, we characterize experimentally the diffusiophoretic motion of colloids and $λ$ -DNA toward higher concentration of solutes, using microfluidic technology to build spatially and temporally controlled concentration gradients. We then demonstrate that segregation and spatial patterning of the particles can be achieved from temporal variations of the solute concentration profile. This segregation takes the form of a strong trapping potential, stemming from an osmotically induced rectification mechanism of the solute time-dependent variations. Depending on the spatial and temporal symmetry of the solute signal, localization patterns with various shapes can be achieved. These results highlight the role of solute contrasts in out-of-equilibrium processes occurring in soft matter.

Received 8 January 2010

DOI:https://doi.org/10.1103/PhysRevLett.104.138302

Authors & Affiliations

Jérémie Palacci¹, Benjamin Abécassis^2,†, Cécile Cottin-Bizonne¹, Christophe Ybert¹, and Lydéric Bocquet^1,*

¹LPMCN; Université de Lyon; Université Lyon 1 and CNRS, UMR 5586; F-69622 Villeurbanne, France
²CEA, LETI, MINATEC, F38054 Grenoble, France

^*lyderic.bocquet@univ-lyon1.fr
^†Present address: MMN, Gulliver, ESPCI 10 rue Vauquelin, 75005 Paris, France.

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Vol. 104, Iss. 13 — 2 April 2010

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Images

Figure 1
(a) Experimental setup (b)-(Left): a 3-channel and gel matrix set-up, superimposed on fluorescence intensity image measured for the stationary gradient of fluorescein with $C_{1} - C_{2} = 10^{- 4} M$ ( $w = 300 μ m$ , $ℓ = 800 μ m$ , scale bar $300 μ m$ ). (b)-(Right): fluorescence intensity profiles measured in stationary state, showing the expected linear profile. Actuation of the microfluidic switch allows us to invert the concentration gradient.Reuse & Permissions
Figure 2
Diffusio-phoretic transport of fluorescent colloids and $λ$ -DNA under a LiCl gradient ( $Δ C_{s} [LiCl] = | C_{2} - C_{1} | = 100 mM$ . $ℓ = 800 μ m$ , scale bar $100 μ m$ ). (a)–(c) Motion of particles under a salt gradient, sketched by the lateral bar, towards higher salt concentrations. Images separated by 90 s for the colloids and images at $t = 100$ , 150, 200, 300 s for $λ$ -DNA. (b)–(d) Time evolution of the particles population location. Experimental data (symbols) are fitted according to the theoretical description (dashed lines), with $D_{DP}$ as the only fitting parameter (see text). In (b), open symbols correspond to a subsequent migration, and fully superimposes on the previous results. The solid straight line in (b) is a guide line corresponding to constant drift velocity. Shaded regions correspond to time periods where wall effects prevent from proper fluorescence measurements.Reuse & Permissions
Figure 3
Trapping under oscillatory gradients: (Top): trapping of colloids, (a), and $λ$ -DNA, (b), under salt gradient oscillations. Salt concentrations are identical to Fig. 2 with $T_{0} = 600 s$ (scale bar $100 μ m$ ). (Bottom): experimental particles density profile in stationary state, as obtained from the fluorescence images (symbols), fitted to a Gaussian curve (dashed line).Reuse & Permissions
Figure 4
Trapping of colloids in a circular chamber: (a)–(b) Initial distribution of the fluorescent colloids and sketch of the experimental setup. The central circular well is $650 μ m$ in diameter with gel walls $125 μ m$ wide ( $ℓ = 900 μ m$ ; scale bar $200 μ m$ ). The salt (LiCl) concentration oscillates in the two side channels (period $T_{0} = 480 s$ ) either antisymmetrically, $C_{1} (t) - ⟨ C_{1} ⟩ = - [C_{2} (t) - ⟨ C_{2} ⟩]$ , or symmetrically $C_{1} (t) = C_{2} (t)$ , between $c_{0} = 100 mM$ and 0 (in addition to a TRIS buffer). (c)–(d): Stationary colloidal distribution under an antisymmetric driving (c) and under symmetric driving (d). ( $c^{'}$ )–( $d^{'}$ ): Theoretical predictions under corresponding experimental conditions. The predicted profiles are those obtained by averaging out the oscillating salt distribution (see text). The values for $D_{DP}$ were taken from experiments in Fig. 2, see Table , while $ℓ$ and $T_{0}$ take their experimental values.Reuse & Permissions

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