How to choose the right dispersant in production? ?

The selection of a suitable dispersant is the focus of recent research, and the most widely used dispersant is a surfactant. Among the surfactants, the more non-hydrophilic ionic groups, the better, because the increase of hydrophilic groups increases the water solubility of the surfactant, and the adsorption on the solid surface is reduced, especially in the mutual interaction between the surfactant and the solid surface. This is especially true in the case of weaker effects.

1. Several criteria that should be considered when selecting a dispersant

1) Under certain conditions, try to use a dispersant that can increase the energy barrier between particles, increase the repulsive force between particles, and make the particles fully dispersed.

2) For oxides and hydroxides and materials containing oxidizing groups, when selecting dispersing agents, attention should be paid to the influence of the pH value of the system on the dispersibility of the materials, and the appropriate dispersing agent should be determined according to the range of pH values.

3) In the case where the particle barrier energy is very low, it is not feasible to add a dispersant capable of increasing the electrostatic repulsion between the particles. It is considered to use a polymer dispersant or a nonionic dispersant to realize the material by the steric effect. Evenly dispersed.

4) Dispersing agents with small amount and high dispersion efficiency should be selected as much as possible, which not only reduces the pollution of the dispersing agent to the classified products, but also reduces the post-processing amount.

2. Type and nature of dispersant

The principle of surface force dispersion regulation of particles in the liquid phase is mainly achieved by adding a suitable dispersant. Its addition significantly enhances the mutual repulsion between the particles, creating the desired physicochemical conditions for the good dispersion of the particles. Enhancing repulsion is mainly achieved in the following three ways. Increasing the absolute value of the surface potential of the particles to improve the electrostatic repulsion between the particles: the steric hindrance effect between the adsorption layers formed on the surface of the particles by the polymer dispersant, resulting in strong steric resistance between the particles; regulating the surface of the particles Polarity enhances the wettability of the dispersion medium. While satisfying the wetting principle, the surface solvation film is enhanced, the surface structuring degree is improved, and the structural repulsive force is greatly enhanced. The dispersion mechanism of different dispersants is not the same.

The following three types of dispersants: inorganic electrolytes, surfactants and polymer dispersants are discussed separately.

2.1 Inorganic electrolyte

Inorganic phosphate with poly (sodium pyrophosphate, trisodium phosphate, tetrasodium phosphate, sodium hexametaphosphate), silicates (sodium metasilicate, sodium disilicate). The adsorption of the inorganic electrolyte dispersant on the surface of the particles not only can significantly increase the absolute value of the surface potential of the particles, thereby generating a strong electrostatic repulsion of the electric double layer, and the inorganic electrolyte can also enhance the degree of wetting of the surface of the particles by water. The adsorption of the inorganic electrolyte on the surface of the particles also enhances the wettability of the surface, increasing the strength and thickness of the solvated film, thereby further enhancing the mutual repulsion of the particles.

2.2 Organic

There are three types of organic types: anionic, nonionic, and cationic. Among them, the anionic type is an alkyl aryl sulfonate, an alkyl benzene sulfonate, a dialkyl sulfo acid salt, a polyethylene glycol alkyl aryl ether sulfonate, etc., and the nonionic type is an alkyl phenol. Polyvinyl ether, sorbitol alkylate, polyoxyethylene alkyl phenol ether, etc., cationic type is alkylpyridinium chloride, trimethyl stearin is chloride or the like. The length of the non-polar group plays a significant role in the modified dispersion of the ultrafine calcium carbonate particles. In water, the order of surface modification of ultrafine calcium carbonate by different polar groups is: -COONa>-Co nHOH >S03H> titanate >-PO(OH)2=silane.

2.3 Polymers

The polymer includes a polycarboxylate, a polyacrylic acid derivative, a maleic acid drunk copolymer, a nonionic water-soluble polymer (polyvinylpyrrolidone, a polyether derivative, polyethylene glycol). The dense adsorption film of the polymer dispersant has a very significant effect on the agglomeration and dispersion state of the particles. A large number of polar groups are almost uniformly distributed on the commonly used organic polymer chains. Therefore, the dense adsorption of organic molecules on the surface of the particles inevitably leads to the hydrophilization of the surface of the particles and enhances the wettability of the surface to the polar liquid. According to the first principle of dispersion control, this facilitates particle dispersion.

The polymer acts as a dispersing agent mainly to make use of its strong steric hindrance repulsion effect on the adsorption film on the surface of the particles. Since the thickness of the adsorbed film of the polymer dispersant can usually reach several tens of nanometers, which is almost equal to or greater than the thickness of the electric double layer, its function begins to appear when the particles are at a considerable distance. The dispersing and agglomeration of the polymeric dispersant can be converted. In general, when the coverage of the polymer adsorption layer on the surface of the particle is much lower than that of a monolayer, the polymer bridges between the particles to cause the particles to flocculate when the coverage of the surface adsorption layer is close to or greater than a single molecule. The layer makes the space compression dominate, and the particles are spatially and stably dispersed by the steric hindrance effect.

When the particles negatively adsorb the high molecular polymer, the polymer concentration of the surface layer of the particles is lower than the bulk concentration of the solution, and a void layer is formed on the surface of the particles. In a low concentration solution, the overlap of the vacancies causes the singularity to attract each other and the granules to vacate and agglomerate. In high concentration solutions, particle repulsion dominates and the particles are stably dispersed in vacancies.

In formulating a dispersion-stable inorganic powder water slurry, the amount of dispersion is not as high as possible, and it has an optimum value. It has been found through research that the dispersant has the optimum range of dosage depending on the solid content of the powder. Generally, the solid content is increased, and the amount of dispersant increases with the increase of the solid content of the powder, further increases the solid content, the distance between the particles decreases, the repulsive force increases, and the amount of the dispersant decreases. For powders of different sizes, the finer the particles, the larger the specific surface area, and the more dispersed dose required to form a stable slurry.

In practical applications, the effect of surfactants on the surface properties of the powder cannot be monolithic. They tend to be dominated by some kind of regulation. At the same time, it has other regulating effects, and sometimes it can increase the repulsive effect, increase the attraction, or reduce the attraction, and reduce the rejection. This requires the determination of the type and concentration of the surfactant by theoretical calculations and targeted experiments.

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