Nicholas Leventis never imagined where his youthful love of science would lead him. “Since I was a child I had an interest in the physical world around me, and I wanted to find out the laws that govern how things work, how nature works,” he explains. “I was ten years old when we went to the moon. All these things started my interest in chemistry and physics.”
It is only appropriate that the moon landing inspired Leventis’ entrance into the field, since his research on aerogels—which he describes as “super lightweight, super low-density solids” similar to Styrofoam—has led him to work with NASA in order to develop new technologies. During his four years with the space program, Leventis was involved with several projects that use cross-linked aerogels—“for lightweight tanks that need to be thermally insulated, for cryogenic liquids like liquid hydrogen and liquid oxygen for storage, and also for [making] space suits thermo-insulating and, at the same time, robust.”
Currently Professor in the Chemistry Department at Missouri University of Science and Technology, Leventis has been working closely with aerogels for years, but his biggest breakthrough came in 2002 with the discovery of a process for cross-linking them. He still remembers the excitement of the innovation: “We came up with the idea based off of curiosity. I did the first two experiments myself, and I engaged other students after that. I wanted some independent researcher to duplicate the findings. So we started with two graduate students; I gave them the recipes and I said, ‘You can duplicate this,’ and they came back with it.”
Aerogels consist of nanoparticles, Leventis explains, which are like honeycombs with walls similar to pearl necklaces. The structure becomes much stronger during cross-linking, when the “interparticle necks” between the beads are reinforced. Leventis differentiates the cross-linking procedure from strengthening honeycombs, nothing that “honeycombs become stronger by adding materials in the walls, making the walls thicker at the expense of the empty space.” Because there are well-defined weak spots on the solid network that forms the aerogel, like the space between the pearls, one can add material specifically to those weak spots so that “the whole structure becomes stronger without compromising much of the empty space that gives the interesting properties of the aerogel.” In the first adaptation of this idea, Leventis used polyurethane chemisty to fill the necks between the nanoparticles.
Developing this process was groundbreaking because cross-linked aerogels are stronger than regular aerogels, which Leventis jokes “can fall apart if you just look at them.” The added strength of cross-linked aerogels gives them countless functions that were once “unthinkable” for their more fragile relatives, ranging from thermal and acoustic insulation to antiballistic protection. Armor made from cross-linked aerogels can stop level three bullets—such as those from sniper rifles—fired from a distance of 15 meters.
Leventis’ other recent research has little to do with the contemporary technological or defensive adaptations of aerogels. In a 2009 co-authored article, “Smelting in the Age of Nano: Iron Aerogels,” he explores the process of smelting as practiced over the past 3000 years, literally from the Bronze Age. Leventis and his peers, Naveen Chandrasekaran, Chariklia Sotiriou-Leventis, and Arif Mumtaz, applied the ancient smelting technique at a nanoscopic level in order to produce nanoporous iron. He describes their work as follows: “we made some aerogels of mixed type, consisting of two interpenetrating networks—one of the inorganic mineral type and another one of the polymer type. When you heat up those mixed aerogels, the two networks react very efficiently, according to the age-old smelting process. The mineral aerogels convert to metal and the polymer aerogels to some carbon gas, like carbon dioxide or monoxide.”
In addition to this research, Leventis is also exploring the possibilities of purely polymeric aerogels. As he explains, “aerogels are of two kinds, inorganic and organic, like the two major sub-categories of matter. The inorganic type has a structural framework that consists of minerals or oxides. The organic type consists of polymers.” While both varieties of aerogels were invented in 1931, until fairly recently only the mineral type was developed.
Interestingly enough, Leventis would probably never have created cross-linked aerogels or experimented with polymeric aerogels had he not decided to change research areas years ago. After obtaining his Ph.D. in organic photochemistry, he switched gears in order to focus on organic materials chemistry. Although these are different disciplines, “the link between them is curiosity,” he notes. “Our research is motivated by curiosity, plain and simple. When we decide to pursue something, we learn whatever is necessary in order to have an understanding. Research is never completed—it is a continuum.”
Aside from satisfying his curiosity, research also complements Leventis’ teaching and vice versa. “Through teaching you find open questions, and you address them through your research,” he observes. He also embraces the chance to involve students in his research, as evidenced by his work with graduate students on cross-linked aerogels. “They make everything possible,” he insists. “None of these projects would be anywhere without them.”
Leventis’ research has benefited from resources aside from student assistance. A grant from the University of Missouri Research Board has been enormously influential on his work: “My experience has been good. The Research Board has been instrumental in getting my projects going.” Specifically, the grant has helped Leventis conduct experiments and provide preliminary results in order to obtain additional grants from the National Science Foundation. As he recalls, “when I came back from NASA in 2006, I received a small seed grant that led to everything we are doing today on polymer-coated aerogels—on interpenetrating networks, on purely organic polymer aerogels, on metal aerogels, and on ceramic aerogels.”
Another instrumental factor in Leventis’ research remains his own curiosity, which he emphasizes has driven him to explore chemistry since childhood and led him to develop revolutionary materials with countless functional applications. A self-described “pioneering spirit,” he offers advice for budding chemists: “Pursue your dreams. Do not be afraid to try new things.” In other words, follow your curiosity and see where it leads. Sound advice from someone who, as a child, was inspired by the moon landing and who went on to develop crucially important materials for the space program.