This story was published in Scientific American.
Eighty years ago, few people in the world had heard of plastics. But in 1939, after its debut at the New York World’s Fair, one type of plastic—nylon—became a household word in less than a year. While nylon took the stockings market by storm, the transition to plastics becoming ubiquitous in clothing and beyond—in kitchenware, electronics, building materials, medicine and more—would take decades. We now know that plastics literally became the material that defined the 20th century.
Looking ahead, metal organic frameworks (MOFs) are poised to be the defining material of the 21st century. While this group of 3-D nanocrystalline structures is still in its early days, its commercial adoption is rapidly accelerating. You have probably never heard of MOFs, but 50 years from now, we believe, they will be an ever-present part of human life just as plastics are today.
CREATING THE NEXT CHEMISTRY POWERHOUSE
What has enabled plastics to become so prevalent in society is their versatility. Plastics are polymers, long repeating strings of monomers that can be swapped out to give them different features. With simple changes to the monomers, polymers can become smaller or larger, softer or harder, stiff or stretchy, opaque or transparent, even electrically conductive.
Like polymers, MOFs are a group of materials with millions of variations for different applications, and they are composed of repeating units of small structures. In this case, the structures are nano-sized metallic clusters with organic molecules linking them. Unlike polymers that grow in only one direction, MOFs build out as crystals in all directions. They have a very rigid, uniform, and precise arrangement of atoms.
This unique uniformity enables scientists to design and engineer MOFs with a precision never before available. By knowing exactly where each atom is located in a MOF, computational tools can rapidly model and simulate different possible structures before needing to synthesize them in a lab. MOFs are currently being used in niche applications, such as stabilizing toxic gases used in fabricating electronics like the silicon chip in your smartphone, but we believe they are on the tipping point, like plastics were 80 years ago.
MOVING TOWARD THAT TEFLON MOMENT
The early 20th century was the heyday of synthetic polymer discovery. But many of the early polymers were unstable, dissolved in water, and lacked flexibility for a wide range of applications.
Nylon was the first widely known, commercially available synthetic polymer. After nylon stockings hit the market, the material next turned up in tents and parachutes for World War II. Around the same time at DuPont, which had also discovered nylon, a scientist accidentally discovered the polymer polytetrafluoroethylene (PTFE). This fluorinated plastic, trademarked as Teflon, had early uses in coating valves and seals of pipes used for radioactive material in the Manhattan Project, but it was relatively unknown. That all changed in 1954 when a French engineer and his wife experimented with using Teflon on cooking pans, leading to the first PTFE-coated, non-stick pans hitting the shelves in the 1960s. So it took roughly 60 years for plastics to reach the consumer masses in multiple industries.
For MOFs, this means we are right on track. After two decades of lab experimentation resulting in many unstable, unreliable and impractical structures, MOFs are now appearing in commercial applications for the first time. But MOFs have yet to have their Teflon moment.
As more companies adopt MOFs, they will continue to make it easier to manufacture MOF-enabled products at lower cost, and their applications will further expand. MOF-based insulation, sound-proof headphones and advanced sensors all could be in the near future. Further down the line, we could be using MOFs to pull carbon from the atmosphere or to help power a new generation of fuel tanks.
And like the serendipitous discovery of Teflon, we could see some serendipitous MOF discoveries along the way. We can imagine DIY paint to soundproof rooms, as the MOFs could produce very thin insulating layers; or MOF-based artificial muscles that could expand or contract along each crystal axis independently. But just as Teflon could not have been predicted 100 years ago, we can’t predict the full scope of possibilities for MOFs
CHARTING THE FUTURE PATH
While there is a clear historic and chemistry precedent for MOFs as established by plastics, what is far less known is the commercial path for the nanomaterial to become ubiquitous. As what happened with plastics, we don’t believe there will be a sharp turning point in the commercialization of MOFs; rather, if costs can come down sufficiently, it will be like water finding its level—MOFs will find broad applications.
Until then, scientists are every day inventing new ways to manufacture MOFs with important real-world applications. They are paving the way to make MOFs the plastics of the 21st century.