Structural Properties of Colloidal Suspensions

JOSE LUIS ARAUZ-LARA Instituto de Fisica Manuel Sandoval Vallarta, Universidad Autonoma de San Luis Potosi, Mexico 

1 Quasi-two-dimensional suspension in the fluid-like phase. The system is formed by polystyrene spheres of diameter 0.5 / m suspended in water. The suspension is confined in a planar slit between two glass plates separated by a distance of twice the diameter of the particles. 

2 Two-dimensional colloidal crystal formed by a single layer of polystyrene spheres of diameter 3 /mi. The particles are initially suspended in water. The crystal is formed by confining the suspension between two glass plates and reducing the separation until it equals the diameter of particles. Here, one can see some typical features of crystals such as defects, fractures and vacancies. 

3 Colloidal aggregate formed in the air-water interface. The aggregated particles are polystyrene spheres of diameter 2.26 /un. In the air-water interface the particles develop an electric-dipole perpendicular to the surface, which prevents them from aggregating. Aggregation is induced by adding to the water solution a small amount of electrolyte which screen the dipolar interaction. In the sample shown here, sulfuric acid was added to the water until a pH of 2 was reached. Courtesy of Prof. Jaime Ruiz-Garcia, Instituto de Fisica, Universidad Autonoma de San Luis Potosi. 

4 Colloidal aggregates of various shapes suspended in water, formed from fluorescent polystyrene spheres of diameter 0.5 /un. 

---