What is the role of dispersant is? How to choose the dispersant?
1. ionic charge
Dispersant mostly ionized electrolyte, anionic moiety thereof preferentially adsorbed to the pigment surface, so that the liquid interface formed between the pigment - negatively charged layer. In the liquid phase, and this negative potential attracts the positively charged ion cloud area (i.e., positive ions area), thereby forming an electric double layer effectively pigment particles repel each other to a large extent dominates the stability of colloidal systems.
It is through the size of the dispersant molecule itself acts. Molecular synthetic resin dispersant is large, it is adsorbed on the pigment particles so that the buffer layer to produce a physical barrier between pigment particles or to form steric hindrance which prevents mutual contact of particles, which play the role of a protective colloid.
Because the dispersant molecules having positively charged and negatively charged electric terminal, so that it can make the water have a special adjacent alignment, thus forming a weak but very important key - hydrogen bond, in the vicinity of the pigment particles to establish a additional buffer layer, which allows the viscosity of the system rises, helps to stabilize the pigment dispersion.
In the electric field, are puzzled dipole molecules from inside - negatively charged center shifted, resulting dipolar molecules, one end of the dipolar molecules are arranged along the surface of the pigment; the liquid toward the other end of the pigment particles repel others that play a protective role in the dispersion.
How reasonable choice dispersant
Any dispersing agent, it is impossible for all pigments, fillers have good dispersion properties. While its pigment and binder has a high selectivity, and therefore choose the dispersant is a meticulous work.
Each dispersants have an HLB value (hydrophilic lipophilic balance). Generally speaking, the majority of inorganic oxides, sulfates, carbonates required dispersant HLB value of 13-20, while the phthalocyanine pigments, yellow sand and organic pigments. An HLB value of about 14 is appropriate, carbon black, Toluidine Red, etc. which is required HLB value 10-13, HLB system can be applied to the choice of the pigment dispersion surfactant.