Sonication

What is Sonication?

Sonication is defined as the process in which sound waves are used to agitate the particles in the solutions. These disruptions are used for mixing of the solutions, to increase the speed of dissolution of a solid into a liquid, and for the removal of dissolved gases from the liquids.

Parts of Sonicator

The equipment used for sonication is known as a sonicator. The following are the three parts of the sonicator:

• A generator
• A transducer
• A probe

The generator is used for transforming the input electrical power into an electrical signal that drives the transducer.

The transducer is used for converting the electrical signal into vibration. This vibration is used in the probe tip by amplifying it into a longitudinal vibration causing a cavity in the sample.

The ultrasound energy is the creation of cavitation which causes the disruption of the sample and makes it easy to break down the particles into smaller ones.

How does Sonication Work?

The sonication process uses ultrasonic sound waves. During the process, there is a production of thousands of microscopic vacuum bubbles in the solution due to applied pressure. The formed bubbles collapse into the solution during the process of cavitation.

The collapsing of bubbles takes place in the cavitation field leading to the generation of enormous energy as there is a production of waves. This results in the disruption of the molecular interactions between the molecules of water. As there is a reduction in the molecular interactions, the particles start to separate and allow the mixing process to take place.

There is a release of energy from the sound waves that result in friction in the solution. Ice cubes are used during and after the sonication process to prevent the sample from heating up.

Principle of Ultra-Sonication

In the ultra-sonication process, cavitation leads to dispersion, homogenization, disintegration, emulsions, extraction, and sonochemical effects of the liquids. High power ultrasound is introduced to the liquid which creates regions of high pressure (known as compression) and low pressure (known as rarefaction). The creation of these regions is dependent on the rate of frequency at which the ultrasound is applied.

When low pressure is applied to the liquid, high-intensity ultrasonic waves are produced, creating small vacuum bubbles in the liquid. As the bubbles reach their saturation level, they collapse and this happens in the high-pressure cycle. This process is termed cavitation. During cavitation, the bubbles in the liquid can jet up to 280 m/s velocities.

The below figure explains how the sound wave propagates in the liquid resulting in the formation of bubbles and their collapse.

Sonication Methods

There are two sonication methods and they are:

• Direct sonication method
• Indirect sonication method

Direct Sonication Method

In the direct sonication method, the probe is directly inserted into the sample, and it is the most common method of sonication. In this method, the energy is transmitted from the probe to the sample directly. This is a high-intensity process and therefore, the processing of the sample takes place quickly. The determination of the volume of the liquid for processing is done by studying the diameter of the probe’s tip. These tips are either replaceable or solid tips made from titanium.

The smaller the diameter of the tip, the higher is the intensity of sonication and the energy is confined to smaller areas. As the diameter of the tip increases, the processing volume becomes larger, however, the intensity becomes lower. The output of the large-diameter probes can be increased by using boosters and high gain horns.

Indirect Sonication Method

In the indirect sonication method, the contact between the probe and the sample is eliminated. This method is also known as the high-intensity ultrasonic bath. The ultrasonic energy is transmitted from the horn to different tubes of the sample through the water. This method is preferred when the volume of the sample is low as it reduces the foaming and loss of the sample.

The indirect sonication method finds application in pathogenic or sterile samples as this method prevents the contamination of the samples. The cup horn and the microplate horn are the two indirect sonicators that are considered ideal for throughput applications.

Uses of Sonication

The following are the uses of sonication:

• The sonication mechanism is used in ultrasonic cleaning which includes cleaning of particles that adhere to the surfaces.
• It is used in laboratories for cleaning fragile objects such as spectacles and jewellery.
• The artificial ageing of liquors and other alcoholic beverages is done by the process of sonication.
• Other applications of sonication in food industries include dispersions of emulgators and speeding the filtration process.
• Different parts of the soil are studied with the help of sonication.

The below is an explanation of the characteristics of sound waves:

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