Electrostatic charging mechanism basic dispersants

Figure 1. Mechanism of electrostatic charging in oil of particles with acidic sites (AH) by a polymeric dispersant with basic sites (B). Reproduced with permission from Ref. (5).Copyright 1982, American Chemical Society.

Figure 1. Mechanism of electrostatic charging of suspended acidic particles (with acidic sites AH) by basic dispersants (with basic sites B) in solvents of low dielectric...

A basic fact of nanoscale materials chemistry is that nanoparticies arc only metastable. The stable state is bulk material. Surface stabilizers are necessary to prevent the particles in a colloidal dispersion from colliding and sticking together. Stabilizers act by an electrostatic mechanism or a steric mechanism or both (16). Particles with like charged surfaces electrostatically repel one another. By the steric mechanism solvated polymer chains extending from the surfaces of two different particles repel one another because the entropy of the system decreases if the polymer chains occupy the same volume. Colloidal dispersions are stable in water or in organic solvents when the stabilizer coordinates to the particle surface and is well solvated. 

Stabilization of colloidal dispersions can be divided into the two basic mechanisms electrostatic and steric (Fig. 4) [57]. With the van der Waals-London attractive forces acting continuously between colloidal particles, it is necessary, in order to maintain stabiUly, to introduce a repulsive force (electrostatic and steric) to outweigh the attractive force. The electrostatic stabilization provides the repulsive forces between similarly charged electrical double layers to the interactive particles [58, 59] (Fig. 4). Thus, the electrical double layer imparts the electrostatic stabilization. The steric stabilization becomes important when there are hydrophilic macromolecules or chains adsorbed or bounded to the particle surface [60]. When the layers of two interacting particles overlap the concentrahon of these macromolecules (chains) increases as weh as free energy. The molecules of good solvent enter the overlap layer and then separate the particles. This phenomenon is accompanied with the increased osmohe pressure. 

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