Carbon Nanotube-enabled ‘Strain Paint’ Could Replace Strain Gauges

Rice researchers keep commercial aspirations for carbon nanotubes alive

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Rice University appears committed to the development of the carbon nanotube (CNT). Ever since its chemistry professor Richard Smalley spun out his research with CNTs into the start-up Carbon Nanotechnologies Inc. (CNI), the university has been inextricably tied to CNTs.

CNI eventually merged with Unidym to create a “nano blockbuster” in 2007,and then it went belly up in 2009. But CNI’s demise had been written on the wall long before that. 

The cautionary tale of CNI is not a knock against the use of carbon nanotubes in commercial applications, but simply a reminder that market pull needs to be more critical to a company’s story than IP position or Nobel Prizes

So, it was pleasing to see that Rice University researchers have not abandoned commercial aspirations for CNTs but instead re-focused their commercial strategies. They have developed a polymeric varnish infused with CNTs that when painted on a surface can act as a strain sensor. The researchers, who have dubbed their material “strain paint,” believe that its early applications could include structures such as airplane wings.

After the “strain paint” has been applied to the surface of a structure and allowed to cure, it is then possible to excite the CNTs that are in the film by focusing a laser beam on the paint. The excited CNTs fluoresce in a way that indicates the amount of strain. More about the research, which was initially published in the American Chemical Society journal Nano Letters, can be found in the video below.


“For an airplane, technicians typically apply conventional strain gauges at specific locations on the wing and subject it to force vibration testing to see how it behaves,” says Satish Nagarajaiah, a Rice professor of civil and environmental engineering and of mechanical engineering and materials science, in a Rice University press release. “They can only do this on the ground and can only measure part of a wing in specific directions and locations where the strain gauges are wired. But with our non-contact technique, they could aim the laser at any point on the wing and get a strain map along any direction,” says Nagarajaiah.

According to Rice chemistry professor Bruce Weisman, some reproducibility and long-term stability of the spectral shifts need to be ironed out before market considerations can be fully explored. “We’ll need to optimize details of its composition and preparation, and find the best way to apply it to the surfaces that will be monitored,” says Weisman in the same press release. “These fabrication/engineering issues should be addressed to ensure proper performance, even before we start working on portable read-out instruments.”

What I like best about the story covering this technology is the final quote from Weisman: “I’m confident that if there were a market, the readout equipment could be miniaturized and packaged. It’s not science fiction.” Exactly.

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Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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