Baby diapers and salt.
Some might find it surprising that these everyday materials can be used in such innovative ways. However, a team of engineers from MIT has developed a super absorbent material capable of extracting a remarkable amount of moisture from the air. It works even in extremely dry conditions, such as when humidity levels are below 30%.
The key is in the… diapers. The key to MIT's innovation lies in the use of hydrogels, which are “slippery, stretchy gels” composed mainly of water and a small amount of cross-linked polymer. In fact, hydrogels are a common material found in disposable baby diapers. Now, MIT researchers have successfully adapted this material to “work just as well to absorb vapor from the air.”
Imagine a group of top engineers and scientists brainstorming in front of a baby diaper. Yes, it's funny.
How did they do it? While searching for solutions to the problem, the researchers found that certain salts are highly effective at extracting vapor from the air. For instance, lithium chloride is “capable of absorbing over 10 times its own mass in moisture.” This means that lithium chloride alone can extract water from the air, but the issue is that it can’t store it, which is what the hydrogel does.
The researchers wondered what would happen if they attempted to combine these two characteristics into one substance.
Not the first researchers to attempt this. In fact, researchers previously discovered that there was a limit to the amount of salt that could be added to such a hydrogel—around “4 to 6 grams of salt per gram of polymer.” Despite this, the results weren’t great, yielding only about 1.5 grams of vapor per gram of material (at 30% relative humidity).
To address this issue, the MIT team took a different approach. Instead of removing the hydrogel from a saline solution after 24-48 hours, as the other researchers had done, they left it immersed for a month.
Absorbing. As expected, the hydrogel continued to incorporate salt until it reached 24 grams. The result is a “transparent, rubbery material” that works much better than the previous iterations. Although the solution isn't a game-changer, it demonstrates a way to achieve success. Afterwards, one can simply heat it up and condense it to obtain pure water. On paper, it looks as promising as it actually is.
Overall, it's because of the applications. Extracting moisture from the air is very useful, even though it may not seem so at first glance. Possible use cases include creating passive water collectors in areas where droughts are common. These technology could also potentially be used in air conditioning equipment, potentially saving energy. The challenge, as always, is making it viable and cost-effective.
The primary concern is not only learning how to produce it quickly and cheaply, but also finding a way to extract the water from the material so that it can be easily recycled.
Image | Gustav Graeber and Carlos D. Díaz-Marín | Emma van Sant via Unsplash
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