Heterogeneous Nucleation and Crystal Growth in Colloidal Model Systems Studied by Confocal Microscopy

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While nucleation and growth of crystals is a longstanding research topic of fundamental and technological importance details of the nucleation process on a microscopic level are still poorly understood. This holds both for ("homogeneous") nucleation in the bulk and for ("heterogeneous") nucleation near surfaces. Suspensions of micron-sized colloidal particles have become valuable model systems for such studies on the single-particle level because of the ease of their observation by conventional or confocal microscopy at all relevant time and length scales, the possible control the interparticle interaction and the recent availability of tools such as optical or magnetic tweezers to conveniently manipulate individual particle positions.The main goal of this project is to reach a detailed understanding of heterogeneous crystal nucleation close to at, curved, rough, and structured surfaces that can either accelerate or suppress nucleation. We will focus on the properties of crystal precursors and critical crystal nuclei which are of prime interest for the nucleation process. We will use polymethylmethacrylate colloids in a index and density matched organic solvent which interact like slightly charged hard spheres. Crystal nuclei of controlled shape, size and symmetry will be generated by an optical multitweezer and the subsequent processes during crystallization observed by confocal microscopy. We also plan to study binary systems composed of particles with different sizes, charges and mixing ratios, with emphasis on the interplay between demixing and crystal growth.