Surfactants play an important role in stabilizing colloidal films. They can reduce surface tension and prevent particle aggregation. Understanding their mechanism helps improve durability, efficiency, and uniformity in products across chemistry, cosmetics, food, and pharmaceuticals.
BASIC CONCEPTS
What is a Surfactant
A surfactant is a compound that can reduce surface tension between two phases such as oil–water or liquid–gas. Its structure includes two parts: a hydrophilic (water-loving) head and a lipophilic (oil-loving) tail. Thanks to this amphiphilic nature, surfactant molecules orient themselves at the phase boundary. This changes the surface energy and helps the dispersion system become more stable and uniform.
Classification of Surfactants
Based on the charge of the polar group, surfactants are divided into four types: anionic, cationic, nonionic, and amphoteric. Anionic types have good foaming ability and are used in detergents and emulsifiers. Cationic surfactants carry a positive charge, have antibacterial effects, and soften surfaces, often used in hair conditioners. Nonionic types are stable in varying pH and salt conditions, suitable for cosmetics and food. Amphoteric types can change charge depending on the medium, increasing compatibility with many colloidal systems.
Colloidal Films and the Need for Stability
A colloidal film is the interfacial layer between two phases in a dispersion system. It is the region with high surface energy. Without stabilizers, particles easily aggregate and separate due to physical interactions or mechanical collisions. When adsorbed on particle surfaces, surfactants form a protective film. This prevents adhesion, maintains particle size, and ensures long-term stability.
MECHANISM OF COLLOIDAL STABILIZATION BY SURFACTANTS
Reduction of Surface Tension
At the phase boundary, surfactant molecules arrange so that the hydrophobic part faces the organic phase and the hydrophilic part faces the dispersing medium. This orientation reduces surface free energy. As a result, the formation of colloidal droplets or dispersed particles becomes easier. The system thus reduces aggregation and phase separation, while increasing long-term stability.
Formation of a Protective Film Around Colloidal Particles
When adsorbed onto particle surfaces, surfactant molecules form a uniform coating around colloidal particles. This coating acts as a barrier, preventing collisions and aggregation. The film also increases local viscosity around particles. It reduces their mobility and limits strong collisions. The presence of water or solvent in this region creates a hydration layer, making the film more flexible and mechanically stable.
Electrostatic and Steric Stabilization
Electrostatic stabilization occurs when particle surfaces carry charges of the same sign, creating repulsive forces that prevent aggregation. Steric stabilization occurs when polar groups or polymer chains extend from the particle surface, forming a physical barrier between particles. Both mechanisms work together to enhance the stability of colloidal systems under various environmental conditions.
Effect of Concentration and Surfactant Type
The stability efficiency depends on the concentration and type of surfactant used. At low concentration, adsorption is insufficient to cover all particle surfaces. When reaching the critical micelle concentration (CMC), micelles form, increasing colloidal stability. The HLB (Hydrophilic–Lipophilic Balance) value also determines emulsifying ability: oil-in-water systems require high HLB surfactants, while water-in-oil systems need low HLB types. Selecting the proper surfactant and concentration ensures optimal stabilization.
PRACTICAL APPLICATIONS AND SIGNIFICANCE
Colloidal film stability provided by surfactants determines product durability and uniformity. In cosmetics, they prevent phase separation between oil and water, maintaining smooth texture and protecting active ingredients. In food, a stable colloidal film keeps milk, cream, or sauces uniform. In pharmaceuticals, a stable film helps particles disperse evenly and enhances drug absorption. In paints and inks, surfactants maintain color stability and improve film coverage.
VICHEM – OFFICIAL DISTRIBUTOR OF CHEMICAL ADDITIVES FROM COVESTRO, SINOPEC, AND TINOX IN VIETNAM
Vichem is the authorized distributor of chemical additives from major global brands such as Covestro, Sinopec, Tinox, and TotalEnergies in Vietnam, fully compliant with local legal regulations. We not only provide high-quality products but also deliver international-standard after-sales services. Our services include:
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