Critical Casimir Interactions: New temperature control of nanoparticle assembly
Institute of Physics, University of Amsterdam
Control over the assembly of colloidal particles has important applications for the design of structures at micrometer and nanometer length scales. In this talk, I will present a new technique to control the assembly of particles with temperature using Critical Casimir forces. This effect allows direct control over the particle pair potential via temperature-dependent solvent fluctuations: In analogy to the confinement of fluctuations of the electromagnetic field between two conducting plates (quantum mechanical Casimir effect), the confinement of fluctuations of a critical solvent leads to an attraction between surfaces that are immersed in this solvent. This allows exquisite temperature control over the interactions of colloidal particles. We show that this dynamic control allows us to form equilibrium phases, as well as quench into well-defined non-equilibrium states. We exploit data taken on the International Space Station as well as on ground. The ideal diffusion-limited aggregation observed in space shows a systematic variation of the fractal dimension of clusters with attractive potential. The gas-liquid equilibrium observed on ground obeys the Van der Waals equation, and follows precisely the universal scaling behavior of molecular gases. The use of confocal microscopy then allows insight into the nucleation of liquids by direct three-dimensional imaging. I will conclude with a perspective on the use of anisotropic particles to assemble complex molecule-like superstructures.