1. Interfacial tension forces on the border of water and bitumen phase separation. The lower the interfacial tension, the easier is the dispergation of the DP, the higher the quality and the emulsion and its dispersion.
2. Type and nature of the emulsifier. As was mentioned above, emulsifier is adsorbed on the surface of DP globules due to their surface energy, therefore lowering the interphase tension and creating an adsorption layer, which prevents globule adhesion, stabilizing the emulsion.
The processes of emulsifier adsorption are quite complex and vary for liquid (soluble in DM) and solid emulsifiers.
3. Emulsifier concentration. Emulsifier significantly decreases interphase tension s even in small concentrations, but it’s quality may be insufficient for creation of even adsorption layer on DP droplets. Therefore, in lower concentrations, the emulsifier promotes dispergation but does not ensure stability of the emulsion. Every emulsifier has a certain concentration, at which it creates an adsorption layer, stabilizing the emulsion.
Fig. 2. Bitumen road emulsion structure: а – O/W on water soluble emulsifier; б – O/W, solid emulsifier; в – W/O, water soluble emulsifier; g– W/O, solid emulsifier; 1 – water solution of emulsifier (dispersion medium); 2 – emulsifierions; 3 – bitumen globule (dispersion phase); 4 – water suspension of solid emulsifier (dispersion medium); 5 – solid emulsifier particles; 6 – globule of emulsifier water solution (dispersion phase); 7 – bitumen (dispersion medium); 8 – globule of water suspension of solid emulsifier (dispersion phase)
At the same time, increase concentration of emulsifier leads to decrease of s to the minimum according to the emulsifier used and the types of DP and DM. This concentration may be considered necessary to form emulsion and to maintain its stability, i.e. it is the optimal concentration.
Further increase of emulsifier concentration has almost no effect on s and emulsion stability. Dispersion of the emulsion does not increase further as well.
Method of emulsifier injection. There are several ways to inject the emulsifier into the system to produce an emulsion. Dissolution in water (for water-soluble compounds) or in bitumen (for oil-soluble compounds.. This method consists of solving emulsifier in water or bitumen and then introducing DP. For anionic emulsions, fatty acid containing emulsifiers are often used, which are indissoluble in water. In this case they are saponified with a base solution to transform to water soluble state. Depending on the nature of the compounds obtained and the order of injecting the solutions into the system, O/W or W/O emulsions may be produced. This process may be treated as a separate operation, by treating emulsifier with fatty acids with base, then solving the resulting soap in water and then using the solution as water emulsifier solution. It is more preferable, however, to saponify fatty acids in the process of emulsion production, i.e. base and emulsifier are introduced in small quantities into the water phase and are then injected into the system. This method is not only simpler, but also allows more rapid formation of emulsifier protective film on the surface of DP droplets as they are dispergated, that is, producing of stable emulsion. Solid emulsifier is introduced into the system for emulsion production as water suspension of mineral powder of required concentration.