A defensive colloid is a term used in the field of colloid chemistry to describe a type of colloidal system that forms when a colloidal suspension of dispersed particles repels or inhibits the aggregation or coagulation of those particles. This repulsion prevents the particles from coming together and settling out, leading to the formation of a stable colloidal dispersion.
Defensive colloids are commonly observed in natural systems, such as in some biological fluids like blood or mucus, where the presence of protective molecules or ions creates repulsive forces between the dispersed particles. These protective agents can be proteins, lipids, or other complex molecules that adsorb onto the particle surfaces, forming a protective layer. This layer, known as the "colloid-protecting layer," creates an energy barrier that hinders the approach of other particles and prevents their aggregation.
The repulsion mechanism in defensive colloids can be electrostatic, steric, or a combination of both. In electrostatic repulsion, like charges are present on the surface of the particles and repel each other due to Coulombic forces. Steric repulsion occurs when the protective layer physically hinders the close approach of particles, preventing their aggregation. The strength of the repulsion depends on factors such as the surface charge, concentration and nature of the protective agents, and the ionic strength of the medium.
Defensive colloids play a critical role in maintaining the stability and functionality of various biological systems, as well as in the production and formulation of colloidal materials, such as in the pharmaceutical, cosmetic, and food industries.
