Colloids are mixtures in which one substance is dispersed evenly throughout another. In a colloidal system, the dispersed particles—called the dispersed phase—are larger than molecules but smaller than what would be visible to the naked eye; typically, they range from about 1 nanometer to 1 micrometer in size. The medium in which the particles are suspended is called the continuous phase or dispersing medium.
Colloids can exist in various forms, depending on the state of the dispersed phase and the continuous phase. Some common types of colloids include:
- Sol: A colloidal solution where solid particles are dispersed in a liquid (e.g., paint, muddy water).
- Gel: A colloid where the liquid is dispersed in a solid (e.g., gelatin).
- Emulsion: A colloid formed by the dispersion of one liquid in another (e.g., milk, mayonnaise).
- Foam: A colloid consisting of gas bubbles dispersed in a liquid or solid (e.g., whipped cream).
- Aerosol: A colloid of fine solid particles or liquid droplets dispersed in gas (e.g., fog, mist, spray).
Colloids are characterized by their ability to scatter light, a phenomenon known as the Tyndall effect, which can be used to distinguish between true solutions and colloids. Due to their unique properties, colloids are used in various applications, including food production, pharmaceuticals, cosmetics, and materials science.