The man who reinvented the hammer
In the early 2000s, while working at a company then called Nanotechnologies, Schroder was applying the concept of pulsed power, a subfield of physics and electrical engineering he’d studied at MIT, to synthesize nanoparticles. Pulsed power involves extremely brief, intense bursts of electric current that deliver “a huge amount of power—a ridiculous amount of power—for a short period of time,” Schroder explains. For example, a flash camera might take five seconds to charge, drawing a mere five watts from an AA battery. But when it releases that stored energy in less than a thousandth of a second, the flash is about 20,000 watts.
“Inventing is a skill, not a talent. Everyone can be an inventor.”
For one of its many projects, the company had been developing an electro-thermal gun, originally intended for military purposes, that Schroder says had “a very intense arc discharge—a spark, but 100,000 amps.” He describes the 50-megawatt prototypes they produced as “a little bit scary” and calls it a “failed device that never got out of the laboratory.” But his predecessors at the company realized that if they pulled the trigger after removing the projectile from the barrel, the high heat of the pulsed arc discharge would erode the silver electrodes inside the barrel, generating plasma that shot out of the device. When the plasma rapidly cooled, these eroded, or ablated, electrodes reacted with gases to form nanoparticles. An inert gas, like helium, would generate silver nanoparticles. A reactive gas would form nanoparticles of a compound, like silver oxide.
Abandoning the idea of an electrothermal gun altogether, Schroder and his colleagues drew on his expertise in pulsed power and focused on applying it to rods of, say, silver or aluminum to produce nanoparticles of those materials. Then they determined that if they tweaked the length of the pulse, from one millisecond to two or more, they could change the average particle size to suit a broader range of applications. The discovery was “really exciting,” Schroder says now, but it proved difficult to capitalize on given the lack of commercial demand for nanoparticles at the time. The company was on the verge of bankruptcy.
Around this time, in 2001, Schroder inherited an ailing 12-year-old German shepherd named Heidi. “She had these pus-y wounds that were a half-inch in diameter and a half-inch deep in her knees and elbows,” Schroder recalls. “The infection was so bad she couldn’t get up.” He began to treat Heidi with a salve made for dogs and horses, but after a couple of weeks she was not improving. “I thought, darn it, I don’t want to put her down,” Schroder remembers.
But then he thought of the silver nanoparticles that his company had developed. “I had heard that some of the stuff might be antimicrobial,” he says. So he mixed the nanoparticles into the salve and applied it to Heidi’s wounds. Within two weeks, they had healed, and Heidi could stand and even run. Now the nanoparticle-infused salve is an FDA-approved product that hospitals use to treat burn victims. “We referred to her, lovingly, as Heidi the Nano Dog,” Schroder says.
Today, Schroder is best known for his second nanoparticle invention, which he dreamed up when he became fascinated with the idea of printed electronics.
“I thought, wouldn’t it be kind of cool if you could take an inkjet printer cartridge, jailbreak it, and [add metallic] nanoparticles and make a dispersion, make an ink?” he says. “You could print wires on a piece of paper and make the cheapest circuit in the world.”
COURTESY OF KURT SCHRODER ’90
The problem is that cheaper substrates, including paper and plastic, will ignite at the high temperatures necessary to sinter, or cure, the nanoparticles into wires. (Melting silver requires a temperature of 962 °C, but paper ignites at 233 °C, or the novelistically famous Fahrenheit 451.) Equally problematic, the ovens in which this sintering takes place are often very large and slow, and they require a lot of energy.
