Thousand of years ago, the Eqyptions and Chinese used naturally occurring polymers to stabilize colloidal dispersions. They mixed carbon black and a polymeric stabilizer (e.g. gum arabic or egg albumin) and then dried the mixture into a pen-like shape. When they needed ink, they dipped the "pen" into water. The carbon black was redispersed immediately to form the ink. In fact, the polymer formed a protective sheath around the colloidal particles to prevent their aggregation. Today, stabilization of colloidal dispersions is widely applied in the paint, electronics, ceramics, oil recovery, food, waste treatment and pharmaceutical science. In pharmaceutical industry, aqueous colloidal dispersions are used as drug carriers and film-coating materials. In the film coating, the water-insoluble polymer is dispersed in an aqueous medium and sprayed onto tablets or beads. For a uniform film coat, the colloidal dispersion must be stable. In addition, aggregated particles may clot the spray nozzles causing trouble to the coating process or even interrupt the film formation process. |
Stabilization of Aqueous Colloidal Dispersions-Basic Concept Zhion, Spring 2006 |