The Role Of Ultrasonic Dispersion in Graphene Preparation

Ultrasonic dispersion is a reliable method to produce graphene layers from graphite flakes or particles. Other common dispersion techniques such as ball mills, roll mills or high shear mixers are susceptible to the use of aggressive reagents and solvents. The ultrasonic dispersion technology can overcome this problem well and prepare graphene materials efficiently.

Ultrasonic dispersion transforms graphene in liquid into a dispersed state, that is, fine or ultrafine ultrasonic grinding of solids or fluids due to the effect of ultrasonic vibrations. Due to the specificity of the ultrasonic field generated in the liquid medium, ultrasonic dispersion provides a highly dispersed uniform, chemically pure suspension (particle size less than 1 μm).

01

The principle of ultrasonic preparation of graphene

Ultrasonic preparation of graphene is based on the cavitation effect, so the quantum structure inside the graphene will not be destroyed. Ultrasonic cavitation generates high-frequency amplitudes through high-power ultrasonic waves. High power ultrasound can be used for the treatment of liquids such as mixing, emulsifying, dispersing and deagglomerating or grinding. When a liquid is sonicated at high intensity, sound waves propagating into the liquid medium cause alternating cycles of high pressure (compression) and low pressure (reflection) at a rate that depends on frequency. High-intensity ultrasonic waves in low-pressure cycles create small vacuum bubbles or voids in the liquid. When the bubbles reach a volume where they cannot absorb the energy, they collapse violently in the high-pressure cycle. This phenomenon is called cavitation.

The ultrasonic dispersion device transmits high-frequency vibrations into the liquid, and the application of this mechanical stress can separate the agglomerates of the graphene particles. When sonicating liquids, sound waves propagating into the liquid medium cause alternating cycles of high pressure (compression) and low pressure (reflection). Ultrasonic cavitation in liquids results in high-velocity liquid jets of up to 1000 km/h (about 600 mph). This jet squeezes the liquid at high pressure between the particles and separates the graphene from each other. Smaller particles are accelerated with the liquid jet and collide at high speed. The high-intensity shock wave generated by the high-speed collision continuously acts on the surface of the graphite body, and the graphite will reflect and generate tensile stress. When a large number of microbubbles are broken, the tensile stress between the graphite flakes increases continuously, and the graphene flakes are gradually exfoliated.

02Exfoliation and dispersion of graphene

If graphene is to be used as a material, it must first be uniformly dispersed in the formulation. Due to the hydrophobicity of graphene, it is difficult to obtain high-concentration graphene dispersions without the stabilization of surfactants or dispersants.

Graphene nanosheets (GNPs) can be fabricated by exfoliating graphite in a solvent by high-power sonication. Ultrasonic exfoliated graphene can be functionalized with biopolymers to obtain water-dispersible graphene. The synthesized graphene can be further processed into stable water-based dispersions by ultrasonic cavitation. Agglomeration easily occurs when graphene nanomaterials are mixed into liquids, and ultrasonic dispersion can break up the agglomerated graphene in aqueous and non-aqueous suspensions, which can bring out the full potential of nanomaterials.

Graphene oxide is water-soluble and can be easily dispersed into stable colloids. Ultrasonic exfoliation and dispersion is a very efficient, fast and cost-effective method to synthesize, disperse and functionalize graphene oxide on an industrial scale. To control the size of graphene oxide (GO) nanosheets, the exfoliation method plays a key role. Due to its precisely controllable process parameters, ultrasonic exfoliation is the most widely used delamination technique for the production of high-quality graphene and graphene oxide.

03Ultrasonic assisted liquid phase exfoliation

Liquid phase exfoliation (LPE) is an efficient method for exfoliation of graphene flakes. The main principle is to add graphite or graphite oxide as a raw material to a specific solvent or surfactant to stir the thermal intercalation to form a graphene pretreatment solution, and then use the ultrasonic waves emitted by a high-power ultrasonic device to peel the graphene from the graphite surface. come out.

Liquid phase peeling method

The main influencing factors of ultrasonic-assisted graphene exfoliation are ultrasonic cavitation and high shear force. The cavitation in the ultrasonic treatment process causes the graphite dispersed in the solvent to be crushed and crushed. The shear force of ultrasonic waves can cause the solvent to form micro-jets to impact the graphite surface, which promotes the separation of graphite layers.

04Summary

High-power ultrasonic systems can be used for exfoliation, dispersion and preparation of graphene and graphene oxide. Reliable ultrasonic processors and advanced reactors provide the power required for graphene processing, with precisely controlled processing conditions that allow the ultrasonic processing results to be precisely tuned to the desired processing target.