In the asphalt-water system, the emulsifier molecules move between the asphalt and water interface, and the water-saving groups of the molecules are adsorbed on the surface of the asphalt and make them charged, while the hydrophilic groups enter the water phase. This connects the asphalt particles with water and reduces the interfacial tension between the two.

At the same time, because the asphalt particles have the same electric charge and repel each other, preventing them from agglomerating with each other, so that the asphalt emulsion can maintain a certain period of uniformity and stability.

The nature of the charge is determined by the charge of the hydrophobic group or hydrocarbon chain part of the emulsifier. If it is negatively charged, the pitch particles are negatively charged, and the formed emulsion is an anionic pitch emulsion. On the contrary, it is a cationic bitumen emulsion. If the asphalt particles have both negative and positive charges, the emulsion is a zwitterionic asphalt emulsion; in addition, there are non-ionic asphalt liquids.