Mechanism of Action​

Electrostatic stabilization and steric hindrance
Dispersants form a double electric layer (anionic types) or a polymer adsorption layer (nonionic types) on the particle surface, generating electrostatic repulsion or steric hindrance effects to inhibit particle agglomeration. For example, anionic dispersants (e.g., polyacrylates) stabilize particles through negative charge repulsion, while nonionic types (e.g., PEG) rely on solvation layers to prevent particle contact.

Wetting and interfacial optimization
The polar groups of dispersants reduce the interfacial tension between the coating liquid and the substrate, enhancing wetting and promoting liquid film spreading. High-molecular-weight dispersants (e.g., PVP) can also form a bilayer on the particle surface, with the outer hydrophilic ends further improving wetting performance.

Viscosity control mechanism
Dispersants effectively regulate the rheological properties of the system through a dual-action mechanism: on one hand, their molecular structures contain specialized functional groups that directionally adsorb onto particle surfaces, forming a stable steric hindrance layer. This significantly reduces van der Waals forces between particles, thereby minimizing inter-particle frictional resistance. On the other hand, dispersants improve interfacial compatibility between different components, facilitating uniform dispersion of particles within the continuous phase. The synergistic effect of these two actions substantially decreases internal friction within the system, manifesting as a notable reduction in macroscopic viscosity. This viscosity control not only enhances the system's fluidity but also optimizes its rheological characteristics, providing an ideal processing window for subsequent manufacturing steps. Additionally, it contributes to improved uniformity and physical properties of the final product.

Dispersion Process

Wetting stage
The dispersant first acts on the gas-solid interface of pigments/fillers, converting it into a liquid-solid interface to reduce surface tension.

Mechanical deagglomeration
Using the shearing force of a high-speed disperser or sand mill, pigment aggregates are broken down into primary particles. At this stage, the dispersant adsorbs onto the freshly exposed surfaces to prevent re-aggregation. Note that the pigment concentration must be sufficiently high to effectively transmit the shearing force.

Stabilization
The dispersed particles remain stable through either a double electric layer (electrokinetic potential) or steric hindrance (e.g., an 8-9 nm adsorption layer). If the counterion concentration is too high, compression of the double electric layer may lead to flocculation (isoelectric point phenomenon).

Key Influencing Factors

Dispersant Type: Anionic dispersants are suitable for high-pH systems, nonionic dispersants exhibit pH insensitivity, while amphoteric dispersants adapt to a wide range of environmental conditions.
Process Parameters: Mechanical shear intensity, pigment solid content (with an optimal volume fraction of 40%-50%), and drying conditions all significantly impact the final dispersion efficiency.

Application Examples
In latex paints, polyacrylic acid-based dispersants are commonly used, combining both electrostatic repulsion and steric hindrance effects. In the paper industry, separate surfactants must be added for difficult-to-wet pigments such as talc to achieve proper wetting.