Plastic and Other Crystals Formed by Colloidal Silica Rods

Orateur : Arnout IMHOF (Debye Institute for Nanomaterials Science, Utrecht University)

Rod-like colloids can serve as a model system to study phenomena such as liquid crystalline phase behavior and anisotropic diffusion on the single particle level. We studied a system of fluorescent rod-like silica colloids using a combination of 3D confocal microscopy and a new single particle tracking technique. When left to sediment, we found that these particles form equilibrium nematic, smectic-B, and orientationally ordered crystals. By integration of the density profile in these sediments we obtained the full equation of state of the system, which we compared with computer simulations on hard spherocylinders. If the rods are made to interact through long range electrostatic repulsion, translational and rotational dynamics decouple and we find plastic crystals and plastic glasses. New insights in the glass transition in this system are obtained by using an electric field to control particle orientations. We also studied a binary smectic liquid crystal phase composed of silica rods and spheres. This phase, which previously has been called a lamellar phase, has spheres filling up the space between smectic rows of rods. The silica rods and spheres were found to interact with almost hard body interactions and the binary smectic phase is believed to form due to entropy, which is confirmed by Monte Carlo simulations of the bulk.

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