Ultrasonic Dispersion of Graphene
To incorporate graphene into composites, it is essential to disperse or exfoliate the graphene into single nano-sheets uniformly throughout the formulation. The more thoroughly the graphene is deagglomerated, the better its extraordinary material properties can be utilized. Ultrasonic dispersion offers superior particle distribution and dispersion stability, even at high concentrations and viscosities. This method provides outstanding dispersion quality, far surpassing conventional mixing techniques.
Ultrasonic Dispersion of Graphene
To imbue composites with the outstanding characteristics of graphene, such as its strength, graphene must be uniformly dispersed into a matrix or applied as a thin-film coating onto a substrate. Key factors influencing the resulting material properties include agglomeration, sedimentation, and the dispersion within the matrix or particle distribution on the substrate.
Due to the hydrophobic nature of graphene, creating a stable and highly concentrated dispersion without surfactants or dispersants is challenging. Overcoming van der Waals forces requires strong shear forces, which can be effectively generated by ultrasonic cavitation. This method is the most sophisticated for preparing stable dispersions.
Industrial sonicators for the high-throughput dispersion of graphene.
More information and technical details about Hielscher industrial probe-type sonicators for graphene exfoliation and dispersion can be found here:
- UIP1000hdT (1000 watts power ultrasound)
- UIP2000hdT (2000 watts power ultrasound)
- UIP4000hdT (4000 watts power ultrasound)
- UIP6000hdT (6000 watts power ultrasound)
- UIP16000hdT (16,000 watts power ultrasound)
All Hielscher sonicators allow for the precise control over all important process parameters, the ultrasonic dispersion technology avoids damages of the chemical and crystal structures of graphene – resulting in pristine, defect-free graphene flakes.
Hielscher powerful ultrasonicators are capable to process graphene and graphite in large volumes, e.g. for liquid-phase exfoliation and graphene dispersion. The exact control over the process parameters allow for the seamless scale-up of ultrasonic processes from bench-top to full-commercial production.
Ultrasonically exfoliated few-layer graphene with approx. 3-4 layers and an approx. size of 1μm can be (re-)dispersed at concentrations of at least 63 mg/mL.
SEM images of graphene nanoplatelets at (b) X3000 and (c) X8000
- high quality graphene
- high throughput? high yields
- uniform dispersion
- high concentration
- high viscosities
- rapid process
- low cost
- highly efficient
- environmental-friendly
7kW ultrasonic reactor for graphene dispersions
Ultrasonic Homogenizers and Disperser for Graphene
Hielscher Ultrasonics provides high-power ultrasonic systems for exfoliating and dispersing bulk-layered graphene and graphite into mono-, bi-, and few-layered graphene. Their reliable ultrasonic processors and advanced reactors deliver the necessary power and precise control to achieve specific process goals.
One of the most essential process parameters is the ultrasonic amplitude, which is the vibrational displacement at the ultrasonic horn. Hielscher industrial ultrasonicators are designed to deliver very high amplitudes, with continuous operation at up to 200µm. For even higher amplitudes, customized ultrasonic probes are available. The process parameters of all Hielscher sonicators can be precisely adjusted to the required process conditions and monitored via built-in software, ensuring high reliability, consistent quality, and reproducible results. The robust design of Hielscher sonicators are built for 24/7 operation in demanding environments, making sonication the preferred technology for large-scale production of mono- and few-layered graphene nanosheets.
Hielscher offers a wide range of ultrasonicators and accessories, including sonotrodes and reactors of various sizes and geometries. This allows for the selection of optimal reaction conditions and factors, such as reagents, ultrasonic energy input per volume, pressure, temperature, and flow rate, to achieve the highest quality. Their ultrasonic reactors can be pressurized up to several hundred barg, making the sonication of highly viscous pastes (up to 250,000 centipoise) feasible.
These capabilities make ultrasonic delamination, exfoliation, and dispersing superior to conventional grinding and milling techniques.
Hielscher sonicators are the most sophisticated ultrasonic homogenizers on the market. Take advantage of the numerous benefits that come with Hielscher sonicators!
Graphic visualizing the ultrasonic synthesis of graphene nanoplatelets using the sonicator UP100H
Hielscher Sonicators for Graphene:
- high power ultrasound
- high shear forces
- high pressures applicable
- precise control
- seamless scalability (linear)
- batch and flow-through
- reproducible results
- reliability
- robustness
- high energy efficiency
Facts Worth Knowing
What is Graphene?
Graphene is a one-atom-thick layer of carbon, which can be described as a single-layer or 2D structure of graphene (single layer graphene = SLG). Graphene has an extraordinarily large specific surface area and superior mechanical properties (Young’s modulus of 1 TPa and intrinsic strength of 130 GPa), offers great electronic and thermal conductivity, charge carrier mobility, transparency, and is impermeable to gases. Due to these material characteristics, graphene is used as reinforcing additive to give composites its strength, conductivity, etc. In order to combine the characteristics of graphene with other materials, graphene must be dispersed into the compound or is applied as a thin-film coating onto a substrate.
Common solvents, which are often used as liquid phase to disperse graphene nanosheets, include Dimethyl sulfoxide (DMSO) , N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), Tetramethylurea (TMU, Tetrahydrofuran (THF), propylene carbonateacetone (PC), ethanol, and formamide.
Can Graphene be Dispersed in Water?
Yes, graphene can be dispersed in water using surfactants, polymers, or other stabilizing agents to prevent aggregation and maintain dispersion stability. Reliable dispersing equipment such as probe-type sonicators play also a crucial role in graphene dispersion by using ultrasonic energy to break up agglomerates and reduce the size of graphene particles, promoting a more uniform and stable dispersion in the liquid medium.
Can Graphene Oxide Dissolve in Water?
Yes, graphene oxide can dissolve in water due to its oxygen-containing functional groups, which enhance its hydrophilicity and allow it to form stable aqueous dispersions.
What is the Best Solvent to Disperse Graphene?
The best solvent to disperse graphene is N-methyl-2-pyrrolidone (NMP) due to its high polarity and ability to stabilize graphene sheets, resulting in a uniform and stable dispersion.
Why is Graphene Insoluble in Water?
Graphene is insoluble in water because it lacks functional groups that can interact with water molecules, making it hydrophobic and prone to aggregation due to strong van der Waals forces between graphene sheets.
Why is Graphene used in Composites?
Graphene is with a thickness of one atom the thinnest, with a weight of approx. 0.77 mg per 1m2 the lightest, and with a tensile stiffness of 150,000,000 psi (100-300 times stronger than steel) and a tensile strength of 130,000,000,000 Pascals the strongest material known.
Furthermore, graphene is the best thermal conductor (at room temperature with (4.84±0.44) × 103 to (5.30±0.48) × 103 W·m-11·K-1) and the best electric conductor (electron mobility higher as 15,000 cm2·V-1·s-1).
Another important characteristics of graphene is its optical property with a light absorption at πα≈2.3% of white light, and its transparent appearance.
By incorporating graphene into matrices, those outstanding material characteristics can be transferred to the resulting composite, which offers unique functionalities. Such graphene-reinforced composites offer new possibilities for material development and industrial applications. Due to its characteristics, graphene and graphene-composites are already widely spread in the manufacturing of high-performance batteries, supercapacitors, conductive inks, coatings, photovoltaic systems and electronic devices
Hielscher sonicators deliver the required high shear forces to overcome van der Waals forces in order to distribute graphene nanosheets uniformly into composite matrices. Ultrasonic dispersers such as the UIP2000hdT or UIP16000 are used to produce graphene- and graphene oxide-reinforced nano-composites.
Literature/References
- FactSheet: Ultrasonic Graphene Exfoliation and Dispersion – Hielscher Ultrasonics – english version
- FactSheet: Exfoliación y Dispersión de Grafeno por Ultrasonidos – Hielscher Ultrasonics – spanish version
- Ivanov R., Hussainova I., Aghayan M., Petrov M. (2014): Graphene Coated Alumina Nanofibres as Zirconia Reinforcement. 9th International DAAAM Baltic Conference of industrial Engineering 24-26 April 2014, Tallinn, Estonia.
- Adam K. Budniak, Niall A. Killilea, Szymon J. Zelewski, Mykhailo Sytnyk, Yaron Kauffmann, Yaron Amouyal, Robert Kudrawiec, Wolfgang Heiss, Efrat Lifshitz (2020): Exfoliated CrPS4 with Promising Photoconductivity. Small Vol.16, Issue1. January 9, 2020.
- Štengl V., Henych J., Slušná M., Ecorchard P. (2014): Ultrasound exfoliation of inorganic analogues of graphene. Nanoscale Research Letters 9(1), 2014.
Hielscher Ultrasonics manufactures high-performance ultrasonic homogenizers from lab to industrial size.