Critical Casimir interactions between colloids around the critical point of binary solvents

Abstract

Critical Casimir interactions between colloidal particles arise from the confinement of fluctuations of a near-critical solvent in the liquid gap between closely-spaced particles. So far, the comparison of theoretical predictions and experimental measurements of critical Casimir forces (CCFs) has focused on the critical solvent composition, while it has been lacking for off-critical compositions. We address this issue by investigating CCFs between spherical colloidal particles around the critical point of a binary solvent through a combination of experiments, previous Ising Monte Carlo simulation results and field-theoretical methods. By measuring the correlation length of the near-critical solvent and the pair potentials of the particles in terms of radial distribution functions and by determining the second virial coefficient, we test in detail theoretical predictions. Our results indicate that the critical Casimir theory gives quantitative correct predictions for the interaction potential between particles in a near critical binary mixture if weak preferential adsorption of the particle surface is taken into account.

Rigidity and auxeticity transitions in networks with strong bond-bending interactions

“…In this work we explored the elastic properties of a model system that represents a material whose mechanics is dominated by bond-bending interactions, rather than the commonly-studied steric or radial interactions. Our study was motivated by recent intriguing experimental work by Schall and coworkers [14], who fabricated colloidal superstructures using critical Casimir forces [39], in which bond-bending interactions between the constituent patchy colloidal particles were shown to be much stiffer than radial ones. In our model system we observe numerically and rationalize theoretically the existence of an angle-preserving isostatic point z c = 4 that governs an underlying jamming transition observed when the ratio of stretching to bending stiffnesses of the interactions vanishes.…”

Collective behavior of colloids due to critical Casimir interactions

“…In Ref. [86] this inaccuracy of the experimental radial distribution function has been compared with the projected theoretical function is the surface counterpart of the bulk gap exponent [87] (see Secs. II B and II B 4).…”

Anisotropic scaling of the two-dimensional Ising model II: surfaces and boundary fields

“…Especially the binary and ternary systems are of special interest for the experimental measurement of the critical Casimir effect [13][14][15], especially for colloidal interactions, as the (lower) critical demixing point is near room temperature in contrast to liquid helium [16,17]. Additionally the surface preferences of the colloidal particles and the containers can be chemically tuned to be either hydrophilic or hydrophobic, which leads to a variety of experimental setups [18][19][20][21][22][23][24].…”