FAQ

Dispersants can be divided into inorganic dispersants and organic dispersants. Among them, inorganic dispersants are ionic dispersants, while organic dispersants are surfactants.

For ionic dispersants, dispersants can ionize positive ions and negative ions after dissolving in water. These ions are adsorbed on the surface of colloidal particles with opposite charges, and then a double electric layer is formed on the surface of the ions, resulting in an increase in zeta potential; for non-ionic dispersants, dispersants are adsorbed on the surface of colloidal particles after dissolving in water, surrounding the particles, forming a steric hindrance, and hindering the contact between the reaction reagent and the reaction center.

Both of these effects will increase the repulsion between particles, resulting in the release of free water wrapped in the aggregate structure. Therefore, dispersants can play the role of dispersing and lubricating particles.

Inorganic dispersants

Inorganic dispersants are some conductive electrolyte compounds that can electrolyze cations and anions when dissolved in water. Inorganic dispersants adsorb ions on the surface of charged particles through ionization, changing the original double layer, thereby increasing the absolute value of the zeta potential and generating a larger electrostatic repulsion, so the colloid has good stability.

(1) Structural formula of sodium tripolyphosphate:

The molecular formula of sodium polyphosphate is Na5P3O10·6H2O (molecular weight: 476.02) or Na5P3O10 (molecular weight: 367.88), also known as sodium triphosphate, pentasodium phosphate, and pentasodium. Sodium tripolyphosphate is easily soluble in water, and the pH value of its aqueous solution is 8-10.

(2) Sodium hexametaphosphate:

The hydrolysis process of hexametaphosphate is as follows:

(NaPO3)6+H2O=6NaOH+6HPO3

HPO3+H2O=H3PO4

H3PO4=H++H2PO4-

H2PO4-=H++HPO42-

HPO4=H++PO43-

Sodium hexametaphosphate belongs to polymetaphosphate. Its molecular structure is cyclic, but it has a linear long chain configuration. It adsorbs to the surface of particles through the end groups, while the middle chain basically does not participate in bonding, which can provide additional electrostatic repulsion. After sodium hexametaphosphate is dissolved in water, the ionized anions are adsorbed on the surface of the particles, increasing the negative charge of the particle surface; in addition, the ionized Na+ ions can increase the thickness of the double layer. Sodium hexametaphosphate has a dispersion effect under these two effects.

Organic dispersants

Organic dispersants (i.e. surfactants) can be divided into ionic surfactants (which can ionize to form ions) and nonionic surfactants (which cannot ionize to form ions). Organic dispersants have a dispersing effect on the system through the following two dispersing mechanisms: For ionic dispersants, electrostatic repulsion and steric hindrance play a role together. If the adsorption layer is thick and the solvation layer is also thick, steric hindrance plays a dominant role; otherwise, electrostatic repulsion plays a role. For nonionic dispersants, steric hindrance plays a dominant role.

(1) Structural formula of citric acid:

The molecular formula of citric acid is C6H8O7. It is an organic electrolyte and an anionic dispersant of organic small molecules. Citric acid is a tribasic acid that can ionize different ions in different pH ranges.

(2) Structural formula of FS10:

FS10 is an ether-based polycarboxylate water reducer with a molecular weight of 10.000 and is an amphoteric surfactant. FS10 consists of a negatively charged main chain and a group of uncharged side chains. The main chain carries more active groups, and the side chains can play a role of lubrication and steric hindrance. Therefore, FS10 not only has the advantages of macromolecular polyelectrolytes, such as steric hindrance and high charge density, but also has the characteristics of excellent mobility of short-chain admixtures.

(3) Structural formula of FDN3000:

The molecular formula of FDN3000 is (C10H6CH2NaSO3)n, which belongs to the naphthalene series of high-efficiency water reducers. After FDN3000 is dissolved in water, the ionized anions are adsorbed on the surface of the particles, increasing the absolute value of the zeta potential, and forming a layer of solvated film to weaken the condensation process between the particles and reduce the friction. Therefore, the particles in the system are dispersed and the fluidity is improved.