The basic working principle is hydrophilicity-lipophilicity balance (HLB). The HLB value is a measure of the relative hydrophilicity or lipophilicity of surfactant molecules. The lower the HLB value (0-9), indicating stronger lipophilicity; the higher the HLB value (11-20), it indicates stronger hydrophilicity. For example, HLB value at 3-6 is suitable for preparing water-in-oil (W/O) emulsions (W/O cream), and HLB value at 8-18 is suitable for making oil-in-water type (O/W) lotion.

Based on this dual-parent structure, surfactants derive a variety of critical functions: 1. Dispersion: The process of dividing solid particles and stably suspending them in a liquid to prevent aggregation and sedimentation. This is crucial in the coatings and pigment industries. 2. Emulsification: The process of stably dispersing one liquid (such as oil) in the form of tiny droplets into another immiscible liquid (such as water) to form an emulsion. Milk, salad dressing, and skincare creams are typical examples of emulsification. 3. Foaming and Defoaming: Surfactants can adsorb at the gas-liquid interface. At the liquid interface, they form and stabilize foam, which is a desirable characteristic in shampoos and toothpaste. However, in industrial cleaning or antibiotic fermentation processes, excessive foam is harmful, necessitating the use of specific low-foaming or defoaming surfactants. 4. Wetting: Reducing the contact angle between a liquid and a solid surface, making it easier for the liquid to spread across the solid surface. This is crucial in pesticide spraying, textile printing and dyeing, and cosmetics research and development.

Surfactants have been widely applied in numerous fields such as detergents, cosmetics, food, pharmaceuticals, and petroleum extraction, becoming indispensable in modern industry and daily life."Industrial MSG".