Dispersants

Chemical nature of dispersants

Most often, dispersants are surfactants or mixtures thereof with different HLB values, which adsorb onto the surface of the dispersed phase particles, reducing the interfacial tension and improving their wettability by the continuous medium. Such adsorption reduces van der Waals interactions between fine particles and enhances repulsive interactions, which helps to keep them separate.

Mechanism of action of dispersants

The mechanism of action of dispersants is based on electrostatic and/or steric stabilisation. In the case of electrostatic stabilisation, ionic dispersants adsorb onto the surface of the particles, giving them a surface charge and forming a so-called double electric layer – the resulting charges cause particles of the same sign to repel each other, which prevents their coagulation.

Steric mechanism

In the steric mechanism, dispersants with a high molar mass (e.g. polymeric) form wide protective layers around the particles, whose spatial veil acts as a physical barrier, making it difficult for the particles to approach and recombine. Steric stabilisation is often less sensitive to the presence of electrolytes than electrostatic stabilisation.

Electro-steric stabilisation

In practice, many modern dispersants combine both mechanisms – so-called electro-steric stabilisation, where electrostatic repulsion and a polymer barrier are generated simultaneously, which increases the stability of the dispersion even under variable chemical conditions, such as pH or ionic strength of the environment.

Application of dispersants

Dispersants are used in many applications, including in the automotive industry as additives to engine oils and in construction as additives to concrete. They can also be found in household and cosmetic chemicals. In the textile industry, they are used as additives to pigments. They are also used in petroleum processing.