Fluid-glass transition in a binary colloidal mixture

Although the fluid-glass transition and glass structure have been studied extensively for many decades, they are still not fully understood. The question still remains as to whether or not the fluid-glass transition is a true thermodynamic phase transition. Neither the structure nor dynamics at the microscopic level are known in great detail.; A binary suspension of highly charged polystyrene spheres in water was used as a model of a metallic glass system. We observed a fluid-glass transition and glass structure near a wall. This system is well-suited for studying both glass transition dynamics and glass structure. The highly charged spheres interact via a soft repulsive Coulomb potential and form a glass at volume fractions ∼0.03. A bidispersion was used in order to suppress nucleation and to enhance glass formation with the introduction of frustration. Digital video microscopy was used to access real time and real space microscopic structure and dynamics. The bidispersion of 0.305 μm and 0.624 μm was selected because it readily formed a glass, and was easily viewed with an optical microscope.; We have mapped out the phase diagram for the bidispersion as a function of the ratio of 0.305μm spheres to 0.624μm spheres vs total volume fraction. We studied in detail a cell with total volume fraction ∼2.5%–3.5% and 0.305μm sphere:0.624μm sphere ratio of 3:1. This cell contained a density gradient where a transition into a kinetically arrested glass was observed. Collective and single particle dynamics were examined. The large spheres became kinetically arrested at lower volume fractions than the smaller spheres. In the dense fluid, sphere motions were highly correlated; hopping was observed. A tiny AB₅ crystallite was heterogeneously nucleated at the coverslip. The three dimensional structure of the crystallite and glass phases were determined. Because the extent of the crystallite was not large enough a computer generated 10 x 10 x 10 AB₅ crystalline lattice was used to study bulk structural properties of the crystalline phase. The glass structure did not show evidence of icosahedral ordering. It did appear to have two layers of large spheres near the wall.