Views:41 Author:Site Editor Publish Time: 2019-08-15 Origin:Site
Under the action of ultrasonic energy, two or more than two kinds of insoluble liquids are mixed together, one of which is dispersed evenly in another liquid to form emulsion liquid. This process is called ultrasonic emulsification.
Emulsion is a dispersion of two or more immiscible solutions. High-intensity ultrasonic provides the energy needed to disperse liquid phase (dispersed phase) in a small droplet of another second phase (continuous phase).
Two types of liquid can form different types of emulsion. For example, oil and water. First of all, water in oil emulsion, in which oil is dispersed phase and water is dispersed medium. Secondly, they can form oil in water emulsion, where water is dispersed phase and oil is outer phase. At the same time, multiple emulsions may be formed, including "water in oil and water in water" emulsion and "oil in water oil" emulsion.
Ultrasonic emulsification is caused by cavitation. The ultrasonic wave passing through the liquid causes it to compress and expand continuously. High-intensity ultrasonic provides the energy needed to disperse the liquid phase. When the maximum pressure is reached, the liquid breaks down at the weak point of cohesion. After the rupture, the overpressure occurs at the point where the rupture occurs, and some cavities are found. In these voids, liquid dissolved gases explode in the form of bubbles in a short time.
In order to stabilize the newly formed dispersed droplets to prevent coalescence, emulsifiers (surfactants, surfactants) and stabilizers were added to the emulsion. The final droplet size distribution is maintained at the same level as the distribution of droplets after breaking up in the ultrasonic dispersion zone.
Cavitation process is affected by the frequency and intensity of ultrasonic. The occurrence of cavitation in the body largely depends on the existence of liquid suspended undissolved gas, which seems to play a catalytic role. Under certain pressure, the formation of the cavity depends to a certain extent on the development time and ultrasonic frequency. The phacoemulsification process represents the competition between opposing processes. Therefore, it is necessary to choose appropriate working conditions and frequency in order to dominate the destructive effect.
Ultrasonic cavitation process
•Control the type of emulsion.
•The power required to produce emulsion is small.
•The emulsion formed is more stable, some stable for several months to more than half a year.
•High concentration, pure emulsion concentration can exceed 30%, and emulsifier can reach 70%.
•Low cost, an important characteristic of ultrasonic emulsification is that it can produce very stable emulsion without or without emulsifier.
•Compared with general emulsification technology and equipment (such as propeller, colloid mill and homogenizer etc.), ultrasonic emulsification has many advantages.
•The average droplet size of the emulsion formed is small (0.2~2 micron), and the droplet size distribution range is narrow (0.1~10 micron) or narrower.
The ultrasonic emulsification equipment can consist of one or more kilowatts of ultrasonic processors, effectively providing the ability to transform laboratory applications into industrial production, and the results are comparable to the best high pressure homogenizer today, so as to obtain fine dispersible emulsion in continuous flow or batch. The maintenance cost of ultrasonic emulsifying equipment is very low, and it is very easy to operate and clean. The power of ultrasonic emulsifying equipment can be adjusted to meet the emulsifying requirements of specific products.
Ultrasonic emulsification technology has been widely used in food, paper making, paint, chemical industry, pharmaceutical, textile, petroleum, metallurgy and other industrial fields. Ultrasonic equipment can be easily installed on existing production lines to facilitate manufacturers to upgrade equipment at a lower cost. Ultrasonic emulsification can also create emulsions that do not work in general methods. The commonly used mixing method can only produce 5% paraffin in water. It is inconceivable that under the action of power ultrasonic, 20% of paraffin emulsion can be made.