A dispersant is a type of surfactant or polymer that reduces the tendency for solid or liquid particles in a liquid medium to aggregate and enables them to remain stably dispersed within the medium.

The following provides a detailed explanation of its definition, classification, and mechanism of action.

I. Definition

A dispersant is a chemical additive that enhances and improves the dispersibility of solid or liquid materials in a liquid medium. It functions by adsorbing onto the surface of the particles, reducing interfacial tension, and creating spatial barriers or electrostatic repulsive forces that prevent the particles from re-aggregating or settling. This results in the formation of a uniform and stable dispersed system.

II. Classification

Based on their chemical structure and mode of action, dispersants can be mainly classified into the following categories:

III. Mechanism of Action

The core function of a dispersant is to overcome the attractive forces (primarily van der Waals forces) between particles and prevent agglomeration. Its mechanism mainly involves the following four aspects:

• Wetting Effect

Dispersants reduce the surface tension of the liquid (water or solvent), improving its ability to wet the surface of solid particles. This allows the liquid to quickly penetrate the gaps between particles, displacing adsorbed air and moisture, thus creating conditions for subsequent dispersion.

• Electrostatic Repulsion Stabilization (Electrical Double Layer Theory)

After adsorption, ionic dispersants impart the same type of charge to particle surfaces, forming an "electrical double layer" around each particle. When two particles approach, the overlapping of their double layers generates electrostatic repulsion. Simultaneously, the dispersant compresses the double layer thickness, preventing particles from colliding and aggregating due to Brownian motion. The magnitude of repulsion is directly related to the particle surface potential (ζ potential) . A high ζ potential is conducive to stability.

• Steric Hindrance Stabilization

The lyophilic (solvent-loving) chains of polymeric or nonionic dispersants extend into the medium, forming a dense "polymer brush" layer on the particle surface. When particles approach, these polymer chains are compressed or interpenetrate, leading to increased local concentration and osmotic pressure, which generates repulsive forces. This steric hindrance effect is less affected by the medium and temperature and is key to preparing high-concentration, highly stable dispersion systems.

• Rheology Modification

Good dispersion can break the network structure formed between particles, releasing trapped medium. This reduces the viscosity of the system and increases its fluidity. This helps improve production efficiency, reduce energy consumption, and enhance the application performance (e.g., coating, casting) of the final product.

Summary

Definition: A substance that reduces inter-particle forces, prevents agglomeration, and achieves a stable dispersion system.

Classification: Based on charge: anionic, cationic, nonionic, amphoteric; based on molecular weight: low molecular weight and high molecular weight.

Mechanism: The core mechanisms are wetting + electrostatic repulsion + steric hindrance. In practical applications, these mechanisms often work synergistically.