The Experiments Of2D Colloidal Crystal And Glass Transition

As the two basic problems of the condensed matter physics, crystallization and glass transition,are a hot topic in recent decades. Under appropriate conditions, colloidal liquid can transform into both order colloidal crystals and disorder colloidal glass. Although crystal and glass exist universally in nature and our daily life, and many advances have been made in the past decades, the understanding of the microscopic mechanism of crystallization and glass transition in colloids is still far from being complete. In this thesis, we experimentally study the colloidal crystallization and glass transition and it will help us to understand the colloidal phase transition and provide reliable guidance for the optimization of the materials.1. Fabrication of large two-dimensional colloidal crystals via self-assembly in an attractive force gradient. Colloidal particles in a water-lutidine (WL) binary liquid mixture experience temperature-dependent attraction close to the mixture’s demixing temperature. This temperature-tunable interaction can be potentially harnessed to assemble colloids and grow colloidal crystals. In this article, for the first time a novel attractive force gradient method is presented to fabricate high-quality, single-domain colloidal crystals. The well-controlled attractive force gradient here arises from a temperature gradient in the WL mixture. The nucleation of colloidal crystals in such a WL mixture preferably occurs in the high-temperature region because of the stronger attraction there. Crystallization propagates from the high-temperature region to the low-temperature region in a well-controlled way. The growth of the colloidal crystal is characterized in detail by Voronoi construction, the pair correlation function, and the orientational order parameter. It is found that the number of crystal-like particles increases with time, and a single-domain2D colloidal crystal can be produced. The mechanism of the defect-free crystallization process is discussed on the basis of an analogy to cluster beam deposition methods.2. Observation of pinning-induced vitrification in two-dimensional colloidal crystal. We experimentally studied the effect of pinning on the structure and dynamics in two-dimensional colloidal crystal. The number fraction of pinning particles is the key to controlling this process. In this paper, we observe that with increasing of number fraction of the pinning particles, the system transforms firstly from a crystal to a polycrystalline state, and then into a glass. The crystal-glass transition shows structural signatures:at the transition point (the number fraction φ=6.9%), the persistence of orientational order decreases sharply from long-range to short range, and the bond orientational order parameter susceptibility exhibits a maximum. The system also shows a sharply variation in particle dynamics:For φ<6.9%, as the number fraction of pinning particles increases, particles move faster due to the generation of some defects near the pinning particles. By contrast, for φ>6.9%, particles move slower when the number fraction of pinning particles increases, because their immobility has a distinct effect (caging of the moving particles). At the transition point (φ=6.9%), the particles move fastest.3. The self-assembly of particles with smooth surface and rough surface in the binary mixture. We use the mixture of water and2,6-lutidine which can produce attraction force close to the mixture’s demixing temperature to induce the self-assembly of the particles with smooth surface and rough surface. In the experiment, we can see that, the particles with smooth surface can get together easily; the particles with rough surface can not get together; the particles with smooth surface and rough surface can get together but not very stable.