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Factors affecting the emulsion of ultrasonic emulsification

Date: 2022-09-27Number: 211

An emulsion is a dispersion of two immiscible liquids, one of which is dispersed in a fine liquid or particle form into another liquid state, resulting in a mixed liquid state. The process of dispersing an immiscible liquid into another immiscible liquid is called an emulsion. The establishment of the emulsion must be carried out the necessary link of the liquid emulsion, which uses mechanical equipment shear stress to pulverize the large liquid dispersion medium in the continuous phase.

Ultrasonic emulsification is a technical means of emulsification, which means that high-frequency vibration is applied to tool head by ultrasonic converter to make two kinds of insoluble liquids mix and produce emulsion. Compared with traditional emulsifying technology, I. E. Ordinary mechanical mixing, ultrasonic treatment can form a super-small liquid state, and the total amount of surfactant needed to bring stable emulsion is generally lower than other technologies.

Ultrasonic emulsification

Factors affecting the emulsion

Sound wave frequency

The working frequency of 20-40kHz can bring the best emulsifying effect, while the shear stress has a greater effect on the emulsifying effect at a lower frequency. With the increase of ultrasonic frequency, the time needed for bubble swelling and cracking is reduced, thus the degree of shear is reduced. At a relatively high operating frequency, the cavitation threshold is raised because more power is required to initiate cavitation, thus reducing the efficiency of the acoustic wave link. The ultrasonic emulsification equipment has a working frequency of 20 to 40 khz can be selected, according to the actual different types of applications to choose the appropriate frequency of the tool head.

Ultrasonic power

Ultrasonic power is one of the important factors to control emulsion emulsion efficiency. With the increase of ultrasonic power, the liquid size of the dispersion medium will decrease. However, when the power input is greater than 200W, the smaller droplets will gather into a larger liquid. These conditions also produce many cavitation bubbles, very high energy density, increased droplet concentration, and high collision probability between liquids. Therefore, it is very important to determine the best power in the Phacoemulsification procedure. With the prolongation of homogenization time, the formation of small droplets will also increase. At the same specific energy, it is possible to compare two emulsifying techniques to check their efficiency in the production of stable emulsions.

Solution temperature

The surface tension and viscosity of the solution decrease with the increase of the temperature, which makes it easier to mix and increases the total number of cavitation bubbles. This trend is very beneficial to the whole emulsification process. However, the effect of increasing temperature on the emulsion is also possible: the cavitation nucleon increases with increasing temperature, and so does the air pressure inside the bubble, the resulting shock wave attenuates and produces many bubbles. This reduces the maximum pressure reached when the bubble implodes. As the total amount of evaporation in the bubble increases, the bubble cracking becomes less intense, which also leads to shear stress and reduced emulsion efficiency.

Sound wave processing time

In general, the increase of the emulsion time will lead to the decrease of the liquid size of the dispersion medium. With the increase of time, the energy of ultrasonic wave in the solution also increases, which leads to the increase of the number of cracked liquid and the decrease of the size of emulsion liquid. However, beyond a certain treatment time, that is, beyond the best treatment time, because the long-term presence of a high concentration of liquid and the collision between the liquid state, smaller droplets will coalesce into a larger liquid state.

Advantages of ultrasonic emulsification

Improve the actual effect of emulsification

According to the liquid size of the dispersion medium, the emulsion can be divided into microemulsion (10-100 nm) , nano-emulsion (100-1000 nm) and large emulsion (0.5-100 μm) . Ultrasound is an effective method to reduce the particle size of dispersions and emulsions. The emulsion with small particle size (only 0.2-2 μm) and narrow liquid size distribution (0.1-10 μm) can be obtained by ultrasonic emulsification equipment, and the concentration of emulsion can be increased by 30% to 70% by using emulsifier.

Enhance emulsion stability

In essence, the emulsion is dynamically unstable and not easily spontaneous, and if its stability is not controlled, it will be separated into its constituent phases. Thus, in order to stabilize the liquid state of the newly formed dispersion medium to prevent coalescence, emulsifiers and stabilizers are added to the emulsion. A stable emulsion can be obtained by using little or no emulsifier. After ultrasonic treatment, the emulsion can remain stable for several months or half a year.

Control the type of emulsion

Under certain conditions, two types of emulsions, “Oil in water” and“Oil in water”, can be produced by ultrasonic technology. The traditional emulsion can only rely on adding emulsifier to control the characteristics of the emulsion, simply through mechanical means can not change the type of emulsion. The ultrasonic emulsification equipment makes the emulsification process more convenient and flexible.

Low power consumption

The power consumption of ultrasonic emulsification is lower than that of homogenizer in producing emulsion with the same capacity. However, the homogenizer needs 4050HP at the working pressure of 70.3351.6 kg/CM2, so the use of ultra-emulsion technology can reduce a lot of energy consumption.

Improve the efficiency of emulsification

Ultrasonic emulsification can bring about emulsions that can not be produced by conventional emulsion methods. As the specific energy increases, the liquid size decreases. At a moderate specific energy level, the average liquid size of less than 1 μm can be achieved. Ultrasound makes the whole emulsification process faster and the resulting emulsion more pure.