A protective colloid is a lyophilic colloid that, when present in small amounts, stabilizes lyophobic colloids by preventing their coagulation or precipitation, especially under the action of electrolytes. It does this by adsorbing onto the surface of the lyophobic colloidal particles, forming a protective layer that prevents the particles from coming together and coagulating
. Key points about protective colloids:
- They are usually lyophilic (water-attracting) colloids like gelatin, starch, gum arabic, or albumin.
- When added to lyophobic (water-repelling) colloids, they increase the stability of the system by preventing coagulation caused by electrolytes.
- The protective layer formed around the lyophobic particles reduces direct collisions and aggregation.
- The effectiveness of a protective colloid is measured by the "gold number," which is the minimum amount (in milligrams) of the protective colloid needed to prevent coagulation of 10 ml of a gold sol on adding 1 ml of 10% sodium chloride solution. A smaller gold number indicates greater protective power
Examples and their approximate gold numbers:
- Gelatin: 0.005–0.01 (high protective action)
- Albumin: 0.1
- Gum Arabic: 0.1–0.2
- Starch: 25 (lower protective action)
Thus, protective colloids play an important role in stabilizing colloidal systems in various industrial and pharmaceutical applications by preventing unwanted coagulation
