Principle and Definition of Electrophoretic Phenomenon

Principle and Definition of Electrophoretic Phenomenon

The molecules, ions, or atoms distributed on the surface of an object are different from those inside the object. Molecules, ions, or atoms on the surface of an object are only attracted by other particles nearby and beneath it. So the particles on the surface of the object have residual attraction, which creates an attractive effect on the surface of the object. When an object is reduced to particle size, the surface area exposed to the surrounding medium is very large. So in colloidal dispersion systems, colloidal particles often attract ions from the medium and carry charges on the dispersed colloidal particles.

The surface composition of different colloidal particles varies. Some of them can attract positive charges, while others can attract negative charges. So some colloidal particles carry positive charges, such as aluminum hydroxide colloids. Some colloidal particles carry negative charges, such as arsenic disulfide (As2S3) colloids. If a direct current is applied to the colloid, they either migrate towards the anode or towards the cathode. This is the so-called electrophoresis phenomenon.

The same type of particles carry the same charge, reducing the possibility of collision between particles and preventing them from combining to form larger particles for precipitation. If electrolytes are added to such colloids, the ions generated by electrolyte ionization will neutralize the charges carried by the colloidal particles, causing them to aggregate and precipitate. The clay particles in the river are negatively charged due to the attraction of hydroxide ions. When river water flows into saline seawater, negatively charged clay particles are neutralized by positively charged sodium and magnesium ions in the seawater, causing the clay to precipitate and eventually forming a delta at the mouth of the river.

In the smoke of a blast furnace, carbon black and dust often appear in the form of colloidal particles and carry electric charges. If a high-voltage electrode is installed on the chimney, it can absorb negatively charged colloidal particles and deposit them. This not only allows for the recovery of valuable products, but also reduces air pollution.

The phenomenon of directional movement of dispersed particles in colloids under the action of an electric field is defined as electrophoresis.