Charged colloids in an aqueous mixture with a salt

We consider a near-critical binary mixture with addition of antagonistic salt confined between weakly charged and selective surfaces. A mesoscopic functional for this system is developed from a microscopic description by a systematic coarse-graining procedure. The functional reduces to the Landau-Brazovskii functional for amphiphilic systems for sufficiently large ratio between the correlation length in the critical binary mixture and the screening length. Our theoretical result agrees with the experimental observation [Sadakane et.al. J. Chem. Phys. 139, 234905 (2013)] that the antagonistic salt and surfactant both lead to a similar mesoscopic structure. For very small salt concentration ρ ion the Casimir potential is the same as in a presence of inorganic salt.For larger ρ ion the Casimir potential takes a minimum followed by a maximum for separations of order of tens of nanometers, and exhibits an oscillatory decay very close to the critical point. For separations of tens of nanometers the potential between surfaces with a linear size of hundreds of nanometers can be of order of k B T . We have verified that in the experimentally studied samples [Sadakane et.al. J. Chem. Phys. 139, 234905 (2013), Leys et.al. Soft Matter 9, 9326 (2013] the decay length is too small compared to the period of oscillations of the Casimir potential, but the oscillatory force could be observed closer to the critical point.

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“…In Refs. [6,16] the OP is identified with the concentration in the binary mixture, ρ * w − ρ * l , while we define the OP in Eq. (10).…”

Section: Discussion and Summarymentioning

confidence: 99%

“…In the latter case the nonlinear coupling between Φ and ρ * q plays a crucial role in our theory, and is ignored in Ref. [6,16].…”

Section: Discussion and Summarymentioning

confidence: 99%

The effect of antagonistic salt on a confined near-critical mixture

Pousaneh

Ciach

2014

Soft Matter

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“…Enhancement of ∆F near the capillary condensation transition is rather obvious in view of the fact that it occurs even in the mean-field theory 24 . Note that ∆F ∝ h 2 1 for weak adsorption (ℓ 0 > D) away from the criticality, where h 1 is the surface field 8 . 2) We have neglected the fluctuations varying in the lateral plane with wavelengths longer than the three-dimensional ξ.…”

Section: Summary and Remarksmentioning

confidence: 99%

Casimir amplitudes and capillary condensation of near-critical fluids between parallel plates: Renormalized local functional theory

Okamoto

Ōnuki

2012

The Journal of Chemical Physics

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120

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We investigate the critical behavior of a near-critical fluid confined between two parallel plates in contact with a reservoir by calculating the order parameter profile and the Casimir amplitudes (for the force density and for the grand potential). Our results are applicable to one-component fluids and binary mixtures. We assume that the walls absorb one of the fluid components selectively for binary mixtures. We propose a renormalized local functional theory accounting for the fluctuation effects. Analysis is performed in the plane of the temperature T and the order parameter in the reservoir ψ∞. Our theory is universal if the physical quantities are scaled appropriately. If the component favored by the walls is slightly poor in the reservoir, there appears a line of first-order phase transition of capillary condensation outside the bulk coexistence curve. The excess adsorption changes discontinuously between condensed and noncondensed states at the transition. With increasing T , the transition line ends at a capillary critical point T = T ca c slightly lower than the bulk critical temperature Tc. The Casimir amplitudes are larger than their critical-point values by 10-100 times at off-critical compositions near the capillary condensation line.

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“…10 The question is then how to predict the phase behavior: because of the complexity of the critical Casimir interactions, the possible importance of many-body effects and the potential coupling between ions and solvent concentration fluctuations, 11,12 there has been much discussion recently about the nature of the interactions and the relevant terms to be included. [13][14][15][16] Effective pair interactions have been discussed to provide a good description of colloidal phase behavior in reasonably dilute suspensions, 13 and such effective interactions have been computed recently based on scaling functions calculated using the Ising model and combined with the Derjaguin approximation, 13 and using simple solvent models with short-range interactions. 17 However, how close such effective potentials and the simulated phase behavior are to the experimental situation remains unclear.…”

Section: Introductionmentioning

confidence: 99%

Temperature-sensitive colloidal phase behavior induced by critical Casimir forces

Dang

Verde

Nguyen

et al. 2013

The Journal of Chemical Physics

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We report Monte Carlo simulations of phase behavior of colloidal suspensions with near-critical binary solvents using effective pair potentials from experiments. At off-critical solvent composition, the calculated phase diagram agrees well with measurements of the experimental system, indicating that many-body effects are limited. Close to the critical composition, however, agreement between experiment and simulation becomes poorer, signaling the increased importance of many-body effects. Both at and off the critical solvent concentration, the colloidal phase diagram is qualitatively similar to those of molecular systems and obeys the principle of corresponding states with one striking difference: it occurs in a narrow temperature interval of <1 • C below the solvent phase separation temperature.

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Charged colloids in an aqueous mixture with a salt

Cited by 49 publications

References 53 publications

The effect of antagonistic salt on a confined near-critical mixture

The effect of antagonistic salt on a confined near-critical mixture

Casimir amplitudes and capillary condensation of near-critical fluids between parallel plates: Renormalized local functional theory

Temperature-sensitive colloidal phase behavior induced by critical Casimir forces

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