Critical Casimir interactions of colloids in micellar critical solutions

Helden, Laurent; Knippenberg, Timo; Tian, Lei; Archambault, Aubin; Ginot, Félix; Bechinger, Clemens

doi:10.1039/d0sm02021d

Cited by 8 publications

(10 citation statements)

References 32 publications

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“…Note that higher ΔT corresponds to a weaker attraction strength in our system, yielding a higher effective temperature. The solvent is an aqueous micellar solution of non-ionic surfactant C 12 E 5 with a lower critical point at T c ≈ 32 °C and 1.2% surfactant weight 25,26 . A binary mixture of silica particles (ratio 0.55:0.45) with diameters σ s = 2.4 μm and σ l = 3.34 μm was added to the solvent which was contained in a sample cell with 100 μm in height.…”

Section: Resultsmentioning

confidence: 99%

“…Due to gravity the particles sediment towards the bottom of the cell where they form a disordered monolayer. The Debye screening length of the system is about 30 nm 26 , leading to rather short-ranged particle repulsion. To create a free surface between a low density gaseous and a high density glass phase, the sample cell was first tilted by 1.15°leading to a lateral density gradient across the sample.…”

Section: Resultsmentioning

confidence: 99%

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Surface melting of a colloidal glass

Tian

Bechinger

2022

Nat Commun

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Despite their technological relevance, a full microscopic understanding of glasses is still lacking. This applies even more to their surfaces whose properties largely differ from that of the bulk material. Here, we experimentally investigate the surface of a two-dimensional glass as a function of the effective temperature. To yield a free surface, we use an attractive colloidal suspension of micron-sized particles interacting via tunable critical Casimir forces. Similar to crystals, we observe surface melting of the glass, i.e., the formation of a liquid film at the surface well below the glass temperature. Underneath, however, we find an unexpected region with bulk density but much faster particle dynamics. It results from connected clusters of highly mobile particles which are formed near the surface and deeply percolate into the underlying material. Because its thickness can reach several tens of particle diameters, this layer may elucidate the poorly understood properties of thin glassy films which find use in many technical applications.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Surface melting of a colloidal glass

Tian

Bechinger

2022

Nat Commun

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“…Further experiments related to CCF are reported in Refs. [136][137][138][139][140][141][142]. The CCF in soft matter systems attract considerable attention because they can be precisely and fully reversibly tuned by small changes of temperature.…”

Section: Critical Casimir Effectmentioning

confidence: 99%

Critical Casimir Effect: Exact Results

Dantchev¹,

Dietrich²

2022

Preprint

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In any medium there are fluctuations due to temperature or due to the quantum nature of its constituents. If a material body is immersed into such a medium, its shape and the properties of its constituents modify the fluctuations in the surrounding medium. If in the same medium there is a second body, modifications of the fluctuation due to the first one influence the modifications due to the second one. This mutual influence results in a force between these bodies. If the excitations of the medium, which mediate the effective interaction between the bodies, are massless, this force is longranged and nowadays known as a Casimir force. If the fluctuating medium consists of the confined electromagnetic field in vacuum, one speaks of the quantum mechanical Casimir effect. In the case that the order parameter of material fields fluctuates -such as differences of number densities or concentrations -and that the corresponding fluctuations of the order parameter are long-ranged, one speaks of the critical Casimir effect. This holds, e.g., in the case of systems which undergo a second-order phase transition and which are thermodynamically located near the corresponding critical point, or for systems with a continuous symmetry exhibiting Goldstone mode excitations. Here we review the currently available exact results concerning the critical Casimir effect in systems encompassing the one-dimensional Ising, XY, and Heisenberg models, the two-dimensional Ising model, the Gaussian and the spherical models, as well as the mean field results for the Ising and the XY model. Special attention is paid to the influence of the boundary conditions on the behavior of the Casimir force. We present results both for the case of classical critical fluctuations if the system possesses a critical point at a non-zero temperature, as well as the case of quantum systems undergoing a continuous phase transition at zero temperature as function of certain parameters. As confinements we consider the film, the sphere -plane, and the sphere -sphere geometries. We discuss systems governed by short-ranged, by subleading long-ranged (i.e., of the van der Waals type), and by leading long-ranged interactions. In order to put the critical Casimir effect into the proper context and in order to make the review as self-contained as possible, basic facts about the theory of phase transitions, the theory of critical phenomena in classical and quantum systems, and finite-size scaling theory are recalled. Whenever possible, a discussion of the relevance of the exact results towards an understanding of available experiments is presented. Hints about eventually applying the results towards their potential use in devices are also given.

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“…[22][23][24] One way to realize selective patch-patch attraction of tunable magnitude is through critical Casimir interactions that depend on the solvent affinity of the particle surfaces. [25][26][27][28] The critical Casimir force arises in binary solvents close to their critical point when the confinement of solvent fluctuations between the particle surfaces causes an effective attractive force on the order of the thermal energy, k B T, tunable by the temperature offset DT from the solvent critical point, T c . [29][30][31] In experimental work on patchy particle systems, investigation of the complex phase behaviour has been rarely reported, with notable exceptions: 6,7,10,12 varying density and attractive strength is an added complexity of an already complex experimental system.…”

Section: Introductionmentioning

confidence: 99%

“…22–24 One way to realize selective patch–patch attraction of tunable magnitude is through critical Casimir interactions that depend on the solvent affinity of the particle surfaces. 25–28 The critical Casimir force arises in binary solvents close to their critical point when the confinement of solvent fluctuations between the particle surfaces causes an effective attractive force on the order of the thermal energy, k B T , tunable by the temperature offset Δ T from the solvent critical point, T c . 29–31…”

Section: Introductionmentioning

confidence: 99%