The principle and process of dispersing agent

Dispersants are surfactants with two opposite properties, lipophilicity and hydrophilicity, in their molecules. They can evenly disperse the solid and liquid particles of inorganic and organic pigments that are difficult to dissolve in liquids, and at the same time prevent the sedimentation and agglomeration of particles, forming amphiphilic agents required for stable suspensions. The role of dispersants is to use wetting dispersants to reduce the time and energy required to complete the dispersion process, stabilize the dispersed pigment dispersion, modify the surface properties of pigment particles, and adjust the mobility of pigment particles.

Specific manifestations are as follows: 1. Improve gloss and increase leveling effect 2. Prevent floating color 3. Improve tinting power 4. Reduce viscosity and increase pigment loading 5. Reduce flocculation 6. Increase storage stability 7. Increase color development, increase color saturation, increase transparency (organic pigments) or hiding power (inorganic pigments)

Mechanism of dispersants / DISPERSANT

1. Adsorb on the surface of solid particles to make the surface of easily agglomerated solid particles easy to wet.

2. The polymer dispersant forms an adsorption layer on the surface of solid particles, which increases the charge on the surface of solid particles and increases the reaction force between particles that form a three-dimensional barrier.

3. The surface of solid particles forms a double-layer structure. The polar end of the outer dispersant has a strong affinity with water, which increases the degree of wetting of solid particles by water. The solid particles are separated by electrostatic repulsion.

4. Make the system uniform, increase the suspension performance, and prevent precipitation, so that the physicochemical properties of the entire system are the same.

Principle of Dispersant / DISPERSANT

1. Double-layer principle The dispersant used in water-based paint must be water-soluble, so that the dispersant will be selectively adsorbed to the interface between powder and water.

Currently, the anionic type is commonly used. They ionize in water to form anions, have a certain surface activity, and are adsorbed on the surface of the powder. After the powder particle surface adsorbs the dispersant, a double layer is formed. The anions are tightly adsorbed on the particle surface and are called surface ions. Ions with opposite charges in the medium are called counterions.

They are electrostatically adsorbed by the surface ions, and some of the counterions are tightly bound to the particles and surface ions, which are called bound counterions. They become a moving whole in the medium, with negative charge, and the other part of the counterions are surrounded by them, which are called free counterions, forming a diffusion layer. In this way, a double layer is formed between the surface ions and counterions.

2. The negative charge of the particles and the positive charge of the diffusion layer form a double layer, which is called the kinetic potential. The thermal potential is the double layer potential formed between all anions and cations.

It is the kinetic potential rather than the thermal potential that plays a dispersive role. The kinetic potential has an unbalanced charge and a charge repulsion phenomenon, while the thermal potential belongs to a charge balance phenomenon.

If the concentration of counterions in the medium is increased, the free counterions in the diffusion layer will be forced to enter the bound counterion layer due to electrostatic repulsion, so that the double layer is compressed and the kinetic potential decreases. When all free counterions become bound counterions, the kinetic potential is zero, which is called the isoelectric point. Without charge repulsion, the system has no stability and flocculation is easy to occur.

3. Steric effect The formation of a stable dispersion system not only utilizes electrostatic repulsion, that is, the negative charges adsorbed on the surface of the particles repel each other to prevent the adsorption/aggregation between particles and finally form large particles and stratification/sedimentation, but also utilizes the theory of steric hindrance effect, that is, when the particles that have been adsorbed with negative charges approach each other, they slide and stagger each other. This type of surfactant that plays a steric hindrance role is generally a non-ionic surfactant.

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