Emulsifier

Emulsifier is a type of substance that can form a stable emulsion from a mixture of two or more immiscible components. The principle of its action is that during the emulsification process, the dispersed phase is dispersed in the form of droplets (micrometer level) in the continuous phase. The emulsifier reduces the interfacial tension of each component in the mixed system and forms a relatively strong thin film on the surface of the droplets or a double layer on the surface of the droplets due to the charge given by the emulsifier, preventing the droplets from aggregating with each other and maintaining a uniform emulsion. From a phase perspective, emulsions are still heterogeneous systems. The dispersed phase in an emulsion can be either the aqueous phase or the oil phase, with the majority being the oil phase; The continuous phase can be an oil phase or a water phase, most of which are water phases. Emulsifier is a surfactant with hydrophilic and oleophilic groups in its molecules. In order to indicate the hydrophilicity or lipophilicity of emulsifiers, the "hydrophilic lipophilic balance value (HLB value)" is usually used. The lower the HLB value, the stronger the lipophilicity; On the contrary, the higher the HLB value, the stronger its hydrophilicity. The HLB values of various emulsifiers are different, and in order to obtain stable emulsions, suitable emulsifiers must be selected.

Emulsification mechanism

Emulsifier is an indispensable component to promote the stability of lotion and plays an important role in the stability of emulsion. In order to form a stable emulsion and disperse the dispersed phase into extremely small droplets, the use and selection of emulsifiers are also important. Emulsifiers mainly form stable emulsions by reducing interfacial free energy and creating a strong emulsion film. Reduce the interfacial free energy and form spherical droplets to maintain the minimum surface area. The process of forming lotion from two different liquids is the process of forming a large number of new interfaces between two-phase liquids. The smaller the droplet, the larger the newly added interface, and the greater the surface free energy of the droplet particles. Emulsifiers adsorb onto the surface of droplets, effectively reducing surface tension or surface free energy. Emulsifiers adsorb around droplets and form a directed film around them, thereby reducing the interfacial tension between oil and water and effectively preventing droplet aggregation. The more neatly emulsifiers are arranged on the surface of droplets, the stronger the emulsion film, and the more stable the emulsion.

The purpose of emulsification is to reduce the energy consumption of lotion preparation. In order to maintain the stability of lotion, emulsifiers should have strong emulsifying ability, form a solid emulsion film, and be safe, non local irritant, stable and less affected by external factors.

The surface effect and stability of emulsifiers

The mechanism of interface formation and stability:

1. The density of emulsifiers is highest at the interface, and the emulsifier molecules form a protective film outside the small droplets. From the perspective of geometric spatial structure, this is reasonable, and from the perspective of energy, it conforms to the principle of minimum energy. Therefore, the emulsion formed is relatively stable;

2. Because the formation of emulsions greatly increases the interfacial area of the system, which requires work to be done on the system, thereby increasing the interfacial energy of the system, leading to system instability. Therefore, reducing its interfacial tension and decreasing the overall interfacial energy can increase the stability of the system; Surfactants, as good emulsifiers, can reduce interfacial tension. According to the principle of "similar solubility", the lipophilic and hydrophilic groups in emulsifiers will insert into the side with the same properties, placing themselves at the water oil interface. During the emulsification process, the amount of emulsifier is inversely proportional to the emulsification temperature. When the emulsification temperature is increased, the distance between liquid molecules increases, and the attraction of the surface layer molecules to the interior of the liquid decreases, resulting in a decrease in surface tension;

3. After the emulsifier is added to the system, a layer of interfacial facial mask is formed while reducing the interfacial tension. The interfacial facial mask has a protective effect on dispersed phase droplets, so that their colliding droplets in Brownian motion are not easy to coalesce. The coalescence (stability destruction) of droplets is based on the rupture of the interfacial facial mask. Therefore, the mechanical strength of the interfacial facial mask is one of the main factors determining the stability of the emulsion.

When the concentration of emulsifier is low, there are fewer molecules adsorbed on the interface, the strength of the interface facial mask is poor, and the emulsion formed is unstable. When the concentration of emulsifier increases to a certain extent, the interfacial facial mask is composed of relatively closely arranged directional adsorbed molecules, which forms an interfacial facial mask with high strength and greatly improves the stability of the emulsion.

Reducing the interfacial tension of the system is a necessary condition for the stability of the emulsion system, while forming a firm interfacial facial mask is a sufficient condition for the stability of the emulsion. The formation of emulsions is the result of natural spontaneous motion, which conforms to the basic rules of spontaneous motion, namely entropy increase and energy decrease.