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The critical Casimir force provides a thermodynamic analogue of the quantum mechanical Casimir force that arises from the confinement of electromagnetic field fluctuations. In its thermodynamic analogue, two surfaces immersed in a critical solvent mixture attract each other due to confinement of solvent concentration fluctuations. Here, we demonstrate the active assembly control of colloidal equilibrium phases using critical Casimir forces. We guide colloidal particles into analogues of molecular liquid and solid phases via exquisite control over their interactions. By measuring the critical Casimir pair potential directly from density fluctuations in the colloidal gas, we obtain insight into liquefaction at small scales. We apply the van der Waals model of molecular liquefaction and show that the colloidal gas–liquid condensation is a...
We present the Rayleigh-Brillouin light scattering data for He + Xe mixtures of various compositions and pressures between 2 and 10 MPa. We compare our experimental data to calculations for a mixture that behaves according to the van der Waals equation of state. Our analysis shows that the contribution of concentration fluctuations to the Landau-Placzek ratio is very important. Furthermore, we demonstrate experimentally the relation between the Landau-Placzek ratio, the adiabatic velocity of sound, and the reduced second moment of the dynamic light scattering spectrum. We show that the van der Waals equation of state can be used to predict the Landau-Placzek ratio in these mixtures quantitatively for mixtures with compositions xu < 0.9. For mixtures with higher xenon concentrations, experimental results agreed quantitatively up to 5 M...
We present new data on Hz + Xe mixtures that support the existence of a fast sound mode in binary gas mixtures. In addition we show that using an approriate scaling, the behaviour of the slow sound mode in systems with different mass ratios, i.e. Hz + Xe, H, + Ar and He + Xe, is identical.
We present experimental evidence that drop breakup is caused by thermal noise in a system with a surface tension that is more than 106 times smaller than that of water.We observe that at very small scales classical hydrodynamics breaks down and the characteristic signatures of pinch-off due to thermal noise are observed. Surprisingly, the noise makes the drop size distribution more uniform, by suppressing the formation of satellite droplets of the smallest sizes. The crossover between deterministic hydrodynamic motion and stochastic thermally driven motion has repercussions for our understanding of small-scale hydrodynamics, important in many problems such as micro- or nanofluidics and interfacial singularities.
The dipole correlation functions determined from far infra-red absorption measurements of a variety of liquids are compared with correlation functions calculated with different models for the motion of the molecules. These models vary from simple rotational diffusion models to models derived from solid state theory. Experimental results are presented of far infra-red measurements of HCl dissolved in liquid argon and of solutions of CH3CN in some organic solvents. For these liquid systems good agreement can be obtained between experiment and model calculations. It is pointed out that the description of these systems in terms of a model has a strong phenomenological character.
By using the critical Casimir force, we study the attractive strength dependent aggregation of colloids with and without gravity by means of near field scattering. Significant differences were seen between microgravity and ground experiments, both in the structure of the formed fractal aggregates as well as in the kinetics of growth. In microgravity purely diffusive aggregation is observed. By using the continuously variable particle interaction potential we can for the first time experimentally relate the strength of attraction between the particles and the structure of the aggregates.
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