Stephen Gibbs literally got to play with fire during his 2015 summer internship. Working on a thermopower wave project with graduate student Tianxiang "Albert" Liu, Gibbs added fuel to short strands of carbon fibers and ignited them from one end. They conducted dozens of similar experiments, measuring magnetic field, voltage, temperature, and length.
"We're converting chemical energy into electrical energy. It's much like a fuel cell, but it's a very different concept fundamentally," explains Liu, a first-year graduate student in the lab of Michael Strano, the Carbon P. Dubbs Professor in Chemical Engineering at MIT. "In layman's terms, basically you are burning the chemical fuel, and there really isn't much of a way to create the oxidation reaction without the flame front; and all the interesting chemistry and all the thermal physics that is going on is embedded within the flame front, that is also called the reaction front."
"I'm very lucky to be a part of the Strano research group for the summer," Gibbs adds. "I want to further our understanding of these reaction waves, these thermopower waves, as much as I can in the nine weeks that I'm here and take with me the experience — the graduate school experience — of researching and implementing the lessons that you've learned from going through the literature."
Gibbs was one of 12 Summer Scholars chosen by the Materials Processing Center (MPC) and Center for Materials Science and Engineering (CMSE) from among 156 applicants this year. They were on campus from June 7 through Aug. 8, and presented their results at a poster session Aug. 5.
Hydrogel materials are prevalent in many avenues of scientific research and engineering applications. However, these materials are often made using a trial-and-error approach with limited understanding of how the microscopic structure in the material affects the desired macroscopic properties. Olivia Fiebig spent her summer investigating two largely similar protein materials. Both of these proteins form gels, but minor substitutions in their amino acid sequences result in two very different materials. Olivia learned how to express and isolate these proteins while working under materials science and engineering graduate student Michelle Sing in the lab of associate professor of chemical engineering Bradley Olsen. Fiebig used a variety of techniques to separate and purify the proteins, including fast protein liquid chromatography. For that process, a solution containing the desirable proteins is injected in a column and slowly separated in an anionic exchange while sodium chloride, the same chemical as common table salt, is added. "Protein is charged and this column has its own charge in it and other molecules could have charge, (or) might not have charge, so you increase the charge in the column over time, with the buffer (sodium chloride)," Fiebig explains. Peaks in a graph plotting response to ultraviolet (UV) light identify the protein. "You can tell which fractions are your protein and which are not," Fiebig says. Once purified, Fiebig then made and mechanically tested these proteins as hydrogels using both rheometry and tensile testing. She learned to freeze-dry samples of purified proteins for future use, a process that is called lyophilization.
Zhenni Lin synthesized hydrogels to use as solid-state magnetic resonance imaging contrast agents and measured their characteristics in David H. Koch Professor of Engineering Michael Cima's lab. The material could potentially be used to measure pH changes inside the body at cancer tumor sites. Lin used nuclear magnetic resonance (NMR) to characterize the different hydrogels.
"After I synthesize the gels, I soak them in different pH buffers and after a few days, I take out small pieces of each sample and test them in this time domain NMR to characterize their relaxation properties," Lin explains. "Since the material that we're trying to make can be used to measure pH internally, we can put the material near a tumor inside the body. By seeing the relaxation properties of the material when it's near the tumor, we can track the pH changes of the tumor. This can help surgeons determine a better course of action for treatment of cancer." Lin worked under graduate student Gregory Ekchian.
Jonah Sengupta's project focused on using novel annealing methods to align block co-polymer films and reduce annealing time. Because the methods being applied in the lab of MIT Professor Karl Berggren haven't been used before, "It would be nice ... if this project turned out nicely," Sengupta says. Preliminary results exhibited small- to large-scale ordering within the block copolymer nanostructures. Future efforts will focus on measuring displacement of the film and eliminating intermediate media, says Amir Tavakkoli Kermani Ghariehali, postdoc in the Quantum Nanostructures and Nanofabrication Group.
Katharine Greco synthesized core-shell quantum dots in the lab of William Tisdale, the Charles and Hilda Roddey Career Development Professor in Chemical Engineering. For her cadmium sulfide shell quantum-dot synthesis, Greco used cadmium oleate and octanethiol precursors. "We're trying to do different things with them, like making pure core/shell dots, and we're also trying to get the two shells to alloy and become graded, or solution state," she explains. Adding liquid hexane helps to dissolve the quantum dots. In this context, "graded" means that the atomic composition gradually changes across the interface between the core and shell material, rather than an atomically abrupt change from one material to the other.
Working on a Schlenk line, Greco synthesized up to 16 samples of core-shell quantum dots each week. Greco used capillaries to slowly inject the precursors into a three-necked flask over a period of up to four hours. One neck was covered with a rubber septum to keep out air. The apparatus can create a vacuum to keep water and oxygen from damaging the synthesis, she says. The core-shell quantum dots glow in different colors when they are held over an ultraviolet light. Samples are stored in a glovebox under nitrogen because they are sensitive to air, so leaving them in air over time would break down their photoluminescence, and the dots wouldn't glow anymore.
Mariely Caraballo Santa worked in the lab of Professor Ronald Ballinger on a project that aims to extend the inspection interval for submarine propulsion shafts up to 12 years. She measured the tensile properties of the submarine shaft material. Caraballo deformed "dogbone" specimens, which were machined from an actual submarine shaft, on a hydraulic testing machine. She recorded the load versus displacement of the specimen and converted this data to stress versus strain.
Lisa Savagian worked in the lab of Paula Hammond, the David H. Koch Professor in Engineering, making films for photothermal drug delivery using a layer-by-layer mechanism. "We have a polymer that's conjugated to a small molecule drug of interest, and we're laying that on top of alternately charged polymers and then incorporating gold nanorods into the film as well, so the drug can be released by an external excitation process," Savagian says. In theory, shining a laser light on the film can speed up the hydrolysis reaction between the polymer film and the drug, so it can enhance the drug delivery process. "I'm making a film that eventually will have a drug polymer conjugated layer on top of it for drug delivery," Savagian explains. "I'm working on the release studies right now and the characterization has been more difficult than we imagined."
Bartholomeus Machielse worked in the lab of Juejun (JJ) Hu, the Merton C. Flemings Assistant Professor in Materials Science and Engineering, on a project to develop tellurium thin films for infrared photonics. "I'm working with chemicals that have flashpoints as low as negative 30 degrees Celsius, which means that in an oxygen environment, they will basically auto ignite any time they come in contact with even a small spark once they are above negative 30 degrees Celsius. Obviously, that's not a practical thing to work with in an oxygen environment, so we are working in an argon environment inside the glovebox," Machielse explains.
Working with a solution of tellurium in a combination of amine and a thiol, Machielse used a dip coater inside the glovebox to deposit a tellurium film onto a silicon oxide on silicon substrate. "The advantage of tellurium films is that they can conduct infrared light up to very long wavelengths. Being able to do it in solution process which is much faster and much easier than a vapor deposition process, would finally make tellurium a material that's accessible for everyday applications. This is one of the first solution-deposited tellurium films ever, and we think with a little bit more tuning we can get useable tellurium films," he says.
Machielse also worked on a project for Department of Materials Science and Engineering Professor Lionel Kimerling's group, taking Raman spectroscopy measurements of a germanium on silicon sample. "What we're exploring now is the effect that annealing has on both the carrier density of germanium samples and the amount of strain that gets carried over from the germanium-silicon interface to the surface of the germanium sample, which will determine the extent to which our bandgap is narrowed," Machielse says.
Alexander Constable worked in professor of aeronautics and astronautics Brian Wardle's lab, where he synthesized aligned carbon nanotube nanocomposites with a carbon matrix, sourcing with PhD student Itai Stein. "This is actually my first experimental lab research experience, so it's been really exciting," Constable says. "Much more hands-on than what I'm used to and I'm learning a lot about operating characterization equipment and analyzing the resulting data."
Constable infused a phenolic resin into a carbon nanotube forest, and then cured it in a furnace at 1,400 degrees Celsius to burn off everything except a carbon matrix with small carbon crystallites growing off of the carbon nanotubes. For analyzing the nanocomposites, Constable used X-ray diffraction techniques known as FTIR and XPS. "For X-ray diffraction we're looking to get the crystallite size based on the full width at half maximum of certain peaks in the 002 and 100 planes. For FTIR, we are just trying to get a better understanding of the vibrational modes of the crystallites within the material. And for X-ray photoelectron spectroscopy (XPS), we're trying to understand the bonding character between the different carbon structures within the composite," he explains.
Small shifts in expected peaks were observed, Constable says. "Just the spectra we're getting in general, it's really minute changes from what would be already considered known, but these small changes are what makes this really new and exciting. These small changes in the spectra actually mean really significant things regarding crystallite size and the evolution of microstructure of the material," he says.
Nathan Zhao investigated inherent stability of nanocrystalline composites in associate professor of materials science and engineering Michael Demkowicz's group. Zhao simulated properties at metal-to-metal interfaces of multilayered metals, which are of interest because of their high strength and resistance to radiation damage.
Lena Barrett sought to uncover a novel catalytic process for producing neopentyl glycol, an important intermediate in industry. Working in the lab of associate professor of chemical engineering Yuriy Román, she ran one-pot batch reactions with beta-structured Lewis acid catalysts and altering various parameters to determine optimal reaction conditions. Barrett worked with PhD student Helen Luo on the project.
Jahzeel Rosado Vega studied wave propagation in spider silk protein fibers using simulation of the molecular structure, under professor of civil and environmental engineering Markus Buehler.
Research associate Sean Bishop presented an update of his research on the chemo-mechanics of solid oxide fuel cells to the MPC-CMSE Summer Scholars on July 31. Solid oxide fuel cells are often subject to dramatic changes in size with composition during operation, known as chemical expansion, and, as his studies show, limiting this kind of expansion is a challenge. Bishop is part of the group of Harry Tuller, professor of ceramics and electronic materials at MIT.
In addition, CMSE research scientist Felice Frankel spoke about her techniques for crafting compelling scientific images for publication and offered guidelines for how to prepare scientific posters on July 17.
The nine-week Summer Scholar research internships are sponsored by the MPC and CMSE. This National Science Foundation (NSF) Research Experience for Undergraduates program is supported under NSF's Materials Research Science and Engineering Centers program (grant number DMR-14-19807).