Manipulation of Colloids by a Nonequilibrium Depletion Force in a Temperature Gradient

Jiang, Hong Ren; Wada, Hirofumi; Yoshinaga, Natsuhiko; Sano, Masaki

doi:10.1103/physrevlett.102.208301

Cited by 221 publications

(285 citation statements)

References 27 publications

Supporting

Mentioning

270

Contrasting

Unclassified

Order By: Relevance

“…The strength of the orientation observed using the present model may appear small. However, it is of the same order as the orientation observed in polar fluids under temperature gradients, which results in significant electrostatic fields, ∼ 10 4 − 10 6 V/m for thermal gradients, 10 6 − 10 8 K/m, which are achievable in experimental set ups [5,22]. Interestingly, the orientation is also similar in magnitude to that observed in water at the liquid-water interface [23].…”

mentioning

confidence: 56%

“…We show that the preferred orientation of the molecules follows the same trends observed in the Soret effect of binary mixtures. We argue this is a general effect that should be observed in a wide range of length scales.Thermal gradients are responsible for a wide range of non equilibrium effects, electron transport (thermoelectricity) [1], mass transport in suspensions (thermophoresis) [2][3][4][5][6], mass separation in liquid mixtures [7][8][9] and nucleation and growth of colloidal crystals [10]. Recently it has been shown that temperature gradients can induce orientation in polar fluids, a physical effect that is supported by Non Equilibrium Thermodynamics Theory (NET) and that can be explained in terms of the coupling of a polarization field and a temperature gradient [11].…”

mentioning

confidence: 99%

See 1 more Smart Citation

Thermomolecular Orientation of Nonpolar Fluids

et al. 2012

View full text Add to dashboard Cite

We investigate the response of molecular fluids to temperature gradients. Using non equilibrium molecular dynamics computer simulations we show that non polar diatomic fluids adopt a preferred orientation as a response to a temperature gradient. We find that the magnitude of this thermomolecular orientation effect is proportional to the strength of the temperature gradient and the degree of molecular anisotropy, as defined by the different size or mass of the molecular atomic sites. We show that the preferred orientation of the molecules follows the same trends observed in the Soret effect of binary mixtures. We argue this is a general effect that should be observed in a wide range of length scales.Thermal gradients are responsible for a wide range of non equilibrium effects, electron transport (thermoelectricity) [1], mass transport in suspensions (thermophoresis) [2][3][4][5][6], mass separation in liquid mixtures [7][8][9] and nucleation and growth of colloidal crystals [10]. Recently it has been shown that temperature gradients can induce orientation in polar fluids, a physical effect that is supported by Non Equilibrium Thermodynamics Theory (NET) and that can be explained in terms of the coupling of a polarization field and a temperature gradient [11]. The polarization of the fluid results in sizable electrostatic fields whose strength scales linearly with the temperature gradient.In this Letter we show that temperature gradients can also induce the molecular orientation of non polar fluids. We call this effect thermomolecular orientation (TMO). The physical origin of this effect cannot be discussed in terms of the polarization field / heat flux coupling, although it is important to note that there is not a principle within non equilibrium thermodynamics theory that precludes observing molecular orientation in non polar fluids. To investigate this hypothesis we use boundary driven non equilibrium molecular dynamics (NEMD) simulations. NEMD has been successfully employed before to investigate thermodynamic and transport properties of atomic and molecular fluids as well as simple ionic liquids [12][13][14][15]. In this work we focus on diatomic fluids. The advantage of using such a model is that it provides simplicity, the necessary "flexibility" to change the molecular anisotropy in a controlled way, and as we will see below, it is possible to establish a direct connection with binary mixtures, making it possible to investigate correlations between TMO and the Soret effect [16,17].We have investigated the TMO effect using a diatomic molecule consisting of two tangent spheres of diameters σ 1 , σ 2 , masses m 1 , m 2 and bond length σ = (σ 1 + σ 2 )/2. The bond length was kept constant using a rigid bond through the Rattle algorithm [18]. The interaction between the particles is completely repulsive, U ij (r) = 4ε (σ ij /r) 12 , where ε is the interaction strength, which we use to define the reduced temperature, T * = k B T /ε, and σ ij = (σ i + σ j )/2 is defined in terms of the diameters of sites i and j. ...

show abstract

mentioning

confidence: 56%

mentioning

confidence: 99%

Thermomolecular Orientation of Nonpolar Fluids

et al. 2012

View full text Add to dashboard Cite

show abstract

“…[20,30,31] the temperature gradient is perpendicular to the boundary as in Fig. 1; a parallel configuration is used in [32,33], with the particles moving along the capillary. The data of [20,[30][31][32] show the behavior S T /a = const.…”

mentioning

confidence: 99%

“…In view of this discrepancy, we complete our discussion of hydrodynamic effects by considering thermophoresis along the boundaries, where confinement is expressed in terms of the ratio of the particle radius a and the width w of the capillary. In view of the experiments [32,33] we consider the perturbative range a w only. In Oseen's model for parallel diffusion, confinement reduces the Stokes-Einstein coefficient of a particle at vertical position z according to D 0 /D = 1 + 9 8 a z + 9 8 a w−z [15].…”

mentioning

confidence: 99%

Hydrodynamic Boundary Effects on Thermophoresis of Confined Colloids

Würger

2016

Phys. Rev. Lett.

View full text Add to dashboard Cite

We study hydrodynamic slowing-down of a particle moving in a temperature gradient perpendicular to a wall. At distances much smaller than the particle radius, h a, lubrication approximation leads to the reduced velocity u/u0 = 3 h a ln a h , with respect to the bulk value u0. With Brenner's result for confined diffusion, we find that the trapping efficiency, or effective Soret coefficient, increases logarithmically as the particle gets very close to the wall. This provides a quantitative explanation for the recently observed enhancement of thermophoretic trapping at short distances. Our discussion of parallel and perpendicular thermophoresis in a capillary, reveals a very a good agreement with five recent experiments on charged polystyrene particles. PACS numbers:The motion of a colloid close to a solid boundary is strongly influenced by hydrodynamic interactions. Thus the like-charge attractions observed for confined colloidal assemblies [2], were shown to arise from hydrodynamic fluctuations [1]. Similarly, a surface-active particle with a flow field perpendicular to the wall, induces lateral advection of nearby neighbors and cluster formation [3][4][5][6][7]. More recently, the collision patterns observed for selfpropelling Janus particles close to a wall [8], were related to hydrodynamic interactions. Quite generally, the latter are relevant where surface forces and confined geometries are combined for sieving [11], trapping [12,13], and assembling colloidal beads [14].A generic example is provided by a surface-active particle moving towards a wall. If hydrodynamic effects on Brownian motion are well understood in terms of Brenner's solution for confined diffusion [15], this is not the case for the drift velocity u. At distances h much larger than the particle radius a, electrophoresis slows down by the factor u/u 0 = 1 − 5 8 a 3 /h 3 [16]. At short distances h < a, the wall-solvent-particle permittivity contrast strongly alters the local electric field; this electric coupling is difficult to separate from hydrodynamic interactions; a similar effect influences diffusiophoresis [17]. A more favorable situation occurs for thermophoresis, where the drift velocity is proportional to the temperature gradient [18,19]: Since the heat conductivity of silica or polystyrene (PS) particles is not very different from that of water, the thermal gradient is hardly affected by the presence of the wall [7], and velocity changes can be unambiguously attributed to hydrodynamic interactions.Here we study the vertical motion of a particle that is confined to the upper half-space z ≥ 0, as illustrated in Fig. 1; applications are thermophoresis across a capillary and self-propelling Janus particles that preferentially orient toward the wall, or "pullers" [10]. In the steady state, drift and diffusion currents cancel each other, −uc − D∇c = 0, and the particle concentration satisfiesAt large distances h a, there are no boundary effects FIG. 1: Schematic view of a particle moving towards a confining wall at velocity u. a) The arrow...

show abstract

“…They are based on either equilibrium thermodynamics [4,5,7,10], a hydrodynamic description [11][12][13], or fluctuating hydrodynamics [14], but no microscopic theory is generally accepted [9,15]. These fundamental issues and possible applications motivate a microfluidic interest in thermophoresis [16][17][18][19][20].…”

mentioning

confidence: 99%