Nanoparticle Dispersion by Ultrasound
A 2012 article in the Journal of Nanomaterials reported on the Dispersion and Stabilization of Photocatalytic TiO2 Nanoparticles in Aqueous Suspension for Coatings Applications.
The article noted that ultrasonication has been proven as a useful tool to disperse nanoparticles and to eliminate agglomeration in aqueous suspensions. It referenced a similar study in the August 2008 issue of the Journal of the American Ceramic Society that compared ultrasonic energy, milling with 5 mm diameter balls and milling with 50µm beads. The JACerS article concludes that nanoparticle dispersion by ultrasound was a useful way to prepare concentrated and highly dispersed nanoparticle suspensions.
Nanoparticle Dispersion in an Ultrasonic Cleaner
Titanium dioxide nanoparticles
Nanowerk.com, Oregon State University
A laboratory ultrasonic cleaner is a useful tool to establish and refine procedures to disperse nanoparticles that then can be scaled up to for production rates. Ideally the ultrasonic cleaner should be able to provide a range of options allowing researchers to develop procedures based on the agglomerates being studied.
The Elmasonic PH series of cleaners available from iUltrasonic in 6 capacities from 0.75 to 7.5 gallons offer features ideally suited to establishing nanoparticle de-agglomeration processes. For this post we’ll use the 1.75 gallon Elmasonic PH175EL with tank dimensions 19.9 x 5.4 x 3.9 inches deep.
Nanoparticle dispersion requires a unit with extremely high power, which is provided by the PH series operating at 100% power. For particularly difficult samples it has a pulse mode that is operator activated to increase the unit’s power by approximately 20% on a pulsed basis at regular intervals. See below for more on power.
Nanoparticle dispersion is typically performed in glass vials and beakers that are suspended in water with a surfactant added to enhance sonication. Sample containers should be immersed 1 to 2 inches in the water but not touch the bottom of the tank. Ultrasonic energy penetrates the glass walls and acts on the samples.
There are options available to suspend the containers in the water. One is using a separately purchased stainless steel basket. For the PH175EL the basket is 18.3 x 4.2 x 2 inches deep. Flask and vial holders can be placed in the basket or as an alternative the containers can be suspended in the water and held by externally supported clamps. Ask our scientists for suggestions based on your particular requirements. The number of samples you treat at a single time will help determine the dimensions of the tank required.
Other Equipment Selection Criteria
As noted above the PH series of equipment has a range of features useful to perform ultrasonic nanoparticle dispersion. In addition to the Pulse mode is its dual range of ultrasonic frequencies: 37 and 80 kHz. The lower frequency provides more vigorous sonication when handling difficult-to-process samples. The equipment can also be set to alternate between 37 and 80 kHz at 30-second intervals.
As noted above ultrasonic power is an important consideration for nanoparticle dispersion, and again the PH series offers researchers some options. Increasing the power increases the intensity of sonication and its effect on nanoparticles being dispersed. But rather than locking researchers in to a fixed power rating the PH series allows them the flexibility of adjusting the ultrasound from 30 percent 100 percent in 10% increments – with a further increase by activating the pulse mode. In the case of the PH175EL effective power when set at 100% is 220 watts.
A Tip on Controlling Temperature
Simply running an ultrasonic cleaner for long periods can cause the liquid temperature to rise to 60?C or more. If temperatures at this level are detrimental to nanoparticle stability simply add ice to the tank or fit it with a cooling coil available from iUltrasonic and connect it to an external circulating cold water supply.
This post should be useful in enabling you to decide on selecting an ultrasonic cleaner for dispersing nanoparticles. Please contact our scientists at 973-440-2191 to discuss additional points or for suggestions on selecting the equipment best suited to your needs.
Ultrasonic Dispersion of TiO2 Nanoparticles in Aqueous Suspension
Journal of the American Ceramic Society August 2008
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