See the bubbles; Quick! Make notes — Background of the development of the PR-1

“We want to disperse nanomaterials safely and in a highly reproducible manner” – In response to such calls, the rotating ultrasonic nano premixer, Nano Premixer PR-1, made its debut. Since it hit the market in February 2017, it has been used by a growing number of people, including scientists and researchers who use nanomaterials. In 2019, it won the Award of Excellence at the Going-Global Innovations Competition sponsored by the Tokyo Metropolitan Government; the PR-1 is one of the devices that has distinguished itself in a manner comparable to the Thinky Mixer.

In this issue, let us share with you how and why the Nano Premixer was developed.

Boston made us do it

In 2007, Thinky took part in a nanotech trade show held in Boston, MA, U.S.A., for the very first time. A visitor came to us with a test material, saying, “I want you to disperse this using the Thinky Mixer right now.” The material was a carbon nanotube (CNT), which was still uncommon in those days, and it was the first time for me to see it. At that time, the Thinky Mixer was no match for it and unfortunately, the demonstration failed.

* The city of Boston (for illustrative purposes only)

As we were groping for a way to address the problem after returning to Japan, a university professor said to us, “If you combine a certain approach with the Thinky Mixer, it would to help disperse nanopowder well. Why don’t we conduct research together?” Although a CNT is a fiber and thus different from powder, upon hearing “nanoparticle dispersion,” we jumped at the chance without hesitation.

Although we will omit the details, in the research, we installed a certain part in the container of the Thinky Mixer to disperse aggregated powders into nanosize particles. The challenge was how to install the part, which proved to be quite tricky, and durability also remained an issue. We ended up failing to commercialize a device and merely published the results of the research in a paper.

At that time, however, the professor shared with us values that were calculated by a supercomputer at the university, to which we normally would have no access, as well as values of the stress that was generated when materials were dispersed. Referring to these data, we discussed how much we should enhance our machine’s specifications and found that we would need to increase the speed of rotation tenfold. Given such a significant shortage of rotation, whether the material was a powder or fiber, it was only natural that it didn’t succeed, wasn’t it? We decided that this idea with the Thinky Mixer was a lost cause and again spent days exploring other strategies. After six months or a year, sometime in 2010, a friend of mine suggested that ultrasonic waves might be effective. After looking into it, we verified that the stress value would surpass the original value.

* Ultrasonic bath (for illustrative purposes only)

We immediately bought ultrasonic equipment and gave it a try. As many people have found, a general horn-type device can disperse a CNT but also fractures it. Meanwhile, the bath-type counterpart did not cause fracture, but neither did it disperse the CNT evenly. With the Thinky Mixer, we had already achieved homogenization by convection, so we thought to adopt a mechanism that rotates the container from the start. But rotation alone did not meet the challenge of “dispersing a CNT evenly without fracturing it,” which, in turn, forced us to think of other creative ways of applying ultrasonic waves.

We consulted a wide variety of ultrasonic equipment manufacturers but found no definitive answer. I gradually began losing hope of victory until one day in 2011, to clear the fogginess in my head and make a fresh start, I went to a nearby sento (public bathhouse). On that day, I happened to be just in time to enjoy a freshly drawn bath*. There were a great many bubbles on the walls of the bathtub. Usually, I pay no attention to these bubbles, but the more I looked, the more they seemed to be like those generated by ultrasonic waves.
(*freshly drawn bath: Bathing in a freshly drawn bath. Also, the freshly heated bathwater.)

* Unbelievably, those bubbles on the walls of the bathtub gave birth to the PR-1!

Then, I thought “what if I radiate an ultrasonic wave from the wall surface?” I vividly remember rushing out of the bathtub and making notes. I later put my idea into practice and checked the state of dispersion with a prototype, with the result being unprecedentedly favorable. This translated into the PR-1’s dual-sonic system.

I think it must have taken seven to eight years to encounter the bubbles in that pristine bath since my first blunder. During that period, I went through one failure after another and learned through trial and error and with much advice from various people. In so far as this development goes, nothing other than perseverance was the key, eclipsing things such as talking about techniques and skill. The development of the PR-1 started with trying to disperse CNTs and now, the machine has come to be used by a wide range of customers with a continuously growing number of applications. When I hear people say, “It’s really helpful,” it makes me profoundly happy and I think it is a true achievement to have been able to put it out onto the market.