Nanodiamonds Dispersed in Aqueous Suspension with Sonication

Nanodiamond dispersions are efficient and quickly produced using ultrasonic dispersers. Ultrasonic deaggregation and dispersion of nanodiamonds can be reliably performed in an aqueous suspension. The ultrasonic dispersion technique uses salt for pH modification and is thereby a facile, inexpensive, and contaminant-free technique, which can be easily used on industrial scale.

Nanodiamonds can be efficient and reliably dispersed using Hielscher ultrasonicators.

How Does Ultrasonic Milling and Dispersion of Nanodiamonds Work?

Ultrasonic dispersion uses the nanodiamonds itself as milling media. Acoustic cavitation generated by high-power ultrasound waves creates high-speed liquid streaming. These liquid streams accelerate the particles (e.g., diamonds) in the slurry so that the particles collide with up to 280km/s and shatter into minute nano-sized particles. This makes ultrasonicmilling and dispersion a facile, inexpensive, and contaminant-free technique, which reliably deagglomerates nanodiamond into nano-sized particles stable in aqueous colloidal solution in a wide pH range. Salt (sodium chloride) is utilized to stabilize the nanodiamonds in an aqueous slurry.


Ultrasonic Nanodiamond Milling Excels Bead Mills

Probe-type ultrasonicators are highly efficacious mills and are an established milling technique for the large-scale production of nanodiamond suspensions on industrial scale. Since ultrasonic mills utilize the nanodiamonds as milling media, contamination through milling media, e.g. from zirconia beads, is completely avoided. Instead, ultrasonic cavitational forces accelerate the particles so that the nanodiamonds collide violently with each other and break down to uniform nano-size. This ultrasonically induced interparticle collision is a highly efficient and reliable method for the production of uniformly distributed nanodispersions.
The ultrasonic dispersion and deaggregation method uses water-soluble, nontoxic, and non-contaminating additives such as sodium chloride or sucrose for pH regulation and stabilization of the ultrasonic dispersion. These crystal structures of sodium chloride or sucrose act additionally as milling media thereby supporting the ultrasonic milling procedure. When the milling process is completed, this additives can be easily removed by a simple rinsing with water, whichis a remarkable advantage over a process ceramic beads. Traditional bead milling such as attritors use insoluble ceramic milling media (e.g. balls, beads, or pearls), whose abrased residuals contaminate the final dispersion. Removal of contamination caused by milling media involves complex after-processing and is time-consuming as well as costly.

Ultrasonic dispersing technology efficaciously produces aqueous nanodiamond suspensions with narrow particle size distribution.
(Study and graphic: ©Turcheniuk et al., 2016)

Exemplary Protocol for Ultrasonic Nanodiamond Dispersion

Salt-Assisted Ultrasonic Deaggregation of Nanodiamonds in Water:
A mixture of 10 g of sodium chloride and 0.250 g of nanodiamond powder was briefly ground by hand using a porcelain mortar and pestle and placed into a 20 mL glass vial along with 5 mL of DI water. The prepared sample was sonicated using a probe-type ultrasonicator for 100 min at 60% output power and 50% duty cycle. After sonication, the sample was equally split between two 50 mL plastic Falcon centrifuge tubes and dispersed in distilled water up to 100 mL total volume (2 × 50 mL). Each sample was then centrifuged using an Eppendorf centrifuge 5810-R at 4000 rpm and 25°C for 10 min, and the clear supernatant was discarded. The wet ND precipitates were then re-dispersed in distilled water (100 mL total volume) and centrifuged a second time at 12000 rpm and 25 °C for 1 h. Once again the clear supernatant was discarded and the wet nanodiamond precipitates were re-dispersed, this time in 5 mL of distilled water for characterization. A standard AgNO3 assay showed complete absence of Cl⁻ in salt-assisted ultrasonically deag
gregated nanodiamonds washed with distilled water twice as described above. After evaporation of water from the samples, formation of black solid nanodiamond “chips” was observed with a yield of ∼200 mg or 80% of the initial nanodiamond mass. (see picture below)
(cf. Turcheniuk et al., 2016)

Dried sample od ultrasonically dispersed nanodiamonds.
(Study and graphic: ©Turcheniuk et al., 2016)

High-Performance Ultrasonicators for Nanodiamond Dispersions

Hielscher Ultrasonics designs, manufactures and distributes high-performance ultrasonic milling and dispersing equipment for heavy-duty applications such as the manufacturing of nanodiamond slurries, polishing media and nanocomposites. Hielscher ultrasonicators are used world-wide for dispersing nano-materials into aqueous colloidal suspensions, polymers, resins, coatings, and other high-performance materials.
Hielscher ultrasonic dispersers are reliable and efficient in processing low to high viscosities. Depending on the input materials and the targeted final particle size, ultrasonic intensity can be precisely adjusted for optimal process results.
In order to process viscous pastes, nano-materials and high solid concentrations, the ultrasonic disperser must be capable to produce continuously high amplitudes. Hielscher Ultrasonics’ industrial ultrasonic processors can deliver very high amplitudes in continuous operation under full load. Amplitudes of up to 200µm can be easily run in 24/7 operation. The option to operate an ultrasonic disperser at high amplitudes and to adjust the amplitude precisely is necessary to adapt the ultrasonic process conditions for the optimum formulation of highly filled nano-slurries, nano-reinforced polymer mixtures and nanocomposites.
Besides the ultrasonic amplitude, pressure is another very important process parameter. Under elevated pressures, the intensity of ultrasonic cavitation and its shear forces is intensified. Hielscher’s ultrasonic reactors can be pressurized thereby obtaining intensified sonication results.
Process monitoring and data recording are important for continuous process standardization and product quality. Pluggable pressure and temperature sensors wire to the ultrasonic generator for monitoring and controlling the ultrasonic dispersion process. All important processing parameters such as ultrasonic energy (net + total), temperature, pressure and time are automatically protocolled and stored onto a built-in SD-card. By accessing the automatically recorded process data, you can revise previous sonication runs and evaluate the process results.
Another user-friendly feature is the browser remote control of our digital ultrasonic systems. Via remote browser control you can start, stop, adjust and monitor your ultrasonic processor remotely from anywhere.
Contact us now to learn more about our high-performance ultrasonic homogenizers for milling and nano-dispersions!
The table below gives you an indication of the approximate processing capacity of our ultrasonicators: