Critical Casimir Effect in Three-Dimensional Ising Systems: Measurements on Binary Wetting Films

Fukuto, Masafumi; Yano, Yohko F.; Pershan, Peter S.

doi:10.1103/physrevlett.94.135702

Cited by 153 publications

(240 citation statements)

References 25 publications

(54 reference statements)

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“…Experimentally, critical Casimir forces have been first measured indirectly by studying the thickness of thin wetting films upon passing thermodynamically a critical end point in the phase diagram of the fluid [13,14]. For classical binary liquid mixtures [15,16] as well as for quantum binary liquids 3 He / 4 He [17,18] and liquid 4 He [19,20] such experiments have provided evidence of the critical Casimir effect in agreement with theoretical results obtained via Monte Carlo (MC) simulations [21][22][23][24][25][26].…”

Section: Introductionsupporting

confidence: 56%

Alignment of cylindrical colloids near chemically patterned substrates induced by critical Casimir torques

et al. 2014

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Recent experiments have demonstrated a fluctuation-induced lateral trapping of spherical colloidal particles immersed in a binary liquid mixture near its critical demixing point and exposed to chemically patterned substrates. Inspired by these experiments, we study this kind of effective interaction, known as the critical Casimir effect, for elongated colloids of cylindrical shape. This adds orientational degrees of freedom. When the colloidal particles are close to a chemically structured substrate, a critical Casimir torque acting on the colloids emerges. We calculate this torque on the basis of the Derjaguin approximation. The range of validity of the latter is assessed via mean-field theory. This assessment shows that the Derjaguin approximation is reliable in experimentally relevant regimes, so that we extend it to Janus particles endowed with opposing adsorption preferences. Our analysis indicates that critical Casimir interactions are capable of achieving well-defined, reversible alignments both of chemically homogeneous and of Janus cylinders.

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Section: Introductionsupporting

confidence: 56%

Alignment of cylindrical colloids near chemically patterned substrates induced by critical Casimir torques

et al. 2014

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“…The techniques introduced can be used to study pressure and fluctuation induced forces in a broad class of nonequilibrium systems. [7,8], and liquid-vapor coexistences [9]. In both cases, quantum and classical, the underlying fluctuations are long-range correlated leading to forces that fall off as power laws.…”

mentioning

confidence: 99%

“…The textbook example is the Casimir force [2,3] arising from quantum fluctuations of the electromagnetic field. Its thermal analog in critical systems [4] has been observed in binary liquid mixtures [5,6], 4 He films [7,8], and liquid-vapor coexistences [9]. In both cases, quantum and classical, the underlying fluctuations are long-range correlated leading to forces that fall off as power laws.…”

mentioning

confidence: 99%

Fluctuation-Induced Forces in Nonequilibrium Diffusive Dynamics

2015

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Fluctuations in nonequilibrium steady states generically lead to power law decay of correlations for conserved quantities. Embedded bodies which constrain fluctuations, in turn, experience fluctuation induced forces. We compute these forces for the simple case of parallel slabs in a driven diffusive system. Our model calculations show that the force falls off with slab separation d as k B T=d (at temperature T, and in all spatial dimensions) but can be attractive or repulsive. Unlike the equilibrium Casimir force, the force amplitude is nonuniversal and explicitly depends on dynamics. The techniques introduced can be used to study pressure and fluctuation induced forces in a broad class of nonequilibrium systems. [7,8], and liquid-vapor coexistences [9]. In both cases, quantum and classical, the underlying fluctuations are long-range correlated leading to forces that fall off as power laws. In the latter (for example, in an oil-water mixture), this is achieved by tuning to a critical point, while the former is a consequence of the massless nature of the photon field. Generically, in a fluid in equilibrium, correlations (and, hence, FIF) decay exponentially and are insignificant beyond a correlation length.Nonequilibrium situations provide another route to longrange correlated fluctuations: Systems which, in equilibrium, have zero or short-ranged correlations [C eq ∼ δ s ðxÞ in s dimensions], quite generically exhibit power law correlations (C neq ∼ 1=jxj α ) with conserved dynamics when out of equilibrium [10][11][12]. Thus, it is natural to inquire about the nature (strength and range) of FIF in corresponding nonequilibrium settings (where there is no matching force in equilibrium). Indeed, such forces have been explored in a number of circumstances, including driven granular fluids [13][14][15][16], shear flow [17], active matter systems [18], and in ordinary fluids due to the Soret effect [19] or subject to a temperature gradient [20,21]. However, despite these studies, they are much less understood than other FIF.Here, we explore FIF in diffusive systems which are far from thermal equilibrium. First, we consider, in detail, possibly the simplest (and, hence, analytically tractable) example of FIF in a system of diffusing particles which are subject only to hard core exclusion. The model is commonly referred to as the symmetric simple exclusion process (SSEP) [22]. Then, we present perturbative results for general diffusive systems. The methods introduced can be used to investigate a large variety of models.The setups examined are as follows: (a) The two dimensional system shown in Fig. 1(a); infinite in the y direction and connected to two reservoirs at x ¼ 0 and x ¼ L, with densities ρð0; yÞ ¼ ρ l and ρðL; yÞ ¼ ρ r , respectively. Two slabs, a distance d from each other, span the system along the x direction. (b) The three dimensional extension of this setup is depicted in Fig. 1(b), with the two slabs replaced by a tube of square cross section. (c) A generalized setup in which the slabs (or tube in three ...

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“…A thermodynamic analogue is the critical Casimir force: it acts between surfaces immersed in a binary liquid mixture dose to its critical point and arises from the confiuement of con centra tion fluctuations within the thin film of fluid separating the sur faces 2 • So far, all ell:peri.mental evidence for the existence of this effect has been indirece 5 • Here we report the direct measurement of critical Casimir force between a single colloidal sphere and a flat silica surface immersed in a mixture of water and 2,6 lutidi.ne near its critical point. We use total internal reflection microscopy to detemti.ue in situ the forces between the sphere and the surface, with femtonewton resolution 6 • Depending on whether the adsorp tion preferences of the sphere and the surface for water and 2,6 lutidi.ne are identical or opposite, we measure attractive and repulsive forces, respectively, that agree quantitatively with theoretical predictions and exhibit exquisite dependence on the temperature of the system.…”

mentioning

confidence: 99%

Direct measurement of critical Casimir forces

Hertlein

Helden

Gambassi

et al. 2008

Nature

542

836

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When fluctuating fields are confined between two surfaces, long range forces arise. A famous example is the quantum electrodynamical Casimir force that results from zero point vacuwn fluctuations confuted between two conducting metal plates'. A thermodynamic analogue is the critical Casimir force: it acts between surfaces immersed in a binary liquid mixture dose to its critical point and arises from the confiuement of con centra tion fluctuations within the thin film of fluid separating the sur faces 2 • So far, all ell:peri.mental evidence for the existence of this effect has been indirece 5 • Here we report the direct measurement of critical Casimir force between a single colloidal sphere and a flat silica surface immersed in a mixture of water and 2,6 lutidi.ne near its critical point. We use total internal reflection microscopy to detemti.ue in situ the forces between the sphere and the surface, with femtonewton resolution 6 • Depending on whether the adsorp tion preferences of the sphere and the surface for water and 2,6 lutidi.ne are identical or opposite, we measure attractive and repulsive forces, respectively, that agree quantitatively with theoretical predictions and exhibit exquisite dependence on the temperature of the system. We expect that these features of critical Casimir forces may result in novel uses of colloids as model systems.The simple act of confining a fluid can give rise to new ph en om en a not observed in the bulk. An intriguing example is the critical Casi.urir force predicted to occur in binary fluid mixtures close to their critical point; like other critical phenomena, it is characterized by universal scaling functions that depend only on the internal symmetries of the system rather than on its specific material properties' . Colloidal particles suspended in binary liquids offer a particularly interesting setting for the experintental observations of such forces. At suffi ciently small particle distances, concentration fluctuations of the solvent become confined between neighbouring colloidal surfaces and modify the pair interaction 8 • If tlte Casinlir interaction strengtlt is comparable to the thermal energy, drastic changes in the phase behaviour are expected. Reversible flocculation of silica colloids in water 2,6 lutidi.ue mixtures close to the critical point has in fact been observed 9 , and critical Casinlir forces may be invoked to explain tills phenomenon. However, flocculation was observed even far away from tlte critical point where critical fluctuations are negligible, so it cannot serve as conclusive evidence for the presence of Casi.utir forces 10 " 11 • Our experiments, ainted at directly measuring critical Casi.utir forces, use a single colloidal sphere and a planar surface immersed in a binary liquid mixture of water and 2,6 lutidine. Forces are deter mined using total internal reflection microscopy (TIRM, see Methods) 6 which allows itt situ measurements with femtonewton resolution 12 (Fig. 1). The binary liquid mixture bas a lower critical demixing point at Tc = ...

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Critical Casimir Effect in Three-Dimensional Ising Systems: Measurements on Binary Wetting Films

Cited by 153 publications

References 25 publications

Alignment of cylindrical colloids near chemically patterned substrates induced by critical Casimir torques

Alignment of cylindrical colloids near chemically patterned substrates induced by critical Casimir torques

Fluctuation-Induced Forces in Nonequilibrium Diffusive Dynamics

Direct measurement of critical Casimir forces

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