Synthesizing thin films for rechargeable batteries, exploring catalysts for the oxygen evolution reaction needed in fuel cells, and testing origami-inspired self-folding materials were among the projects tackled by 14 summer scholars in MIT labs.
The interns — chosen from among 256 applicants in a highly competitive process — were part of a Summer Scholars Program for undergraduate students, jointly run by the Materials Processing Center (MPC) and the Center for Materials Science and Engineering (CMSE).
Self-folding laminates
Meredith Fields built and tested self-folding hinges in origami-inspired laminates whose folding action is triggered by electricity. Fields worked in the lab of associate professor of mechanical engineering John Hart, who also is examining self-folding triggered by blue LED light.
To study the mechanical behavior of laminate hinges, Fields created the laminates by laser cutting paper hinges, applying a pressure-sensitive adhesive and attaching a biaxially pre-strained polymer, such as PVC or polyethylene, to the adhesive. The self-folding mechanism can be activated by electricity, heat or light.
“I’m testing an electrically actuated system, in which I flow current through conductive carbon, and when I do that, it heats the conductive carbon and through conduction heats the hinge. Since it’s a heat sensitive polymer it will shrink and create a fold, so this is the basis of self-folding hinges,” Fields says. The millimeter-to centimeter-scale laminates have a potential to be used in batteries.
“Meredith will have the experience of preparing a conference presentation and she’s been doing some other great work on mechanical design,” graduate student Abhinav Rao says. Fields contributed to a presentation by Hart for the sixth International Meeting of Origami Science, Mathematics and Education (OSME) conference in Japan in August.
Developing microbatteries
Rahul Kini experimented with building thin film batteries in the lab of professor of materials science and engineering Carl V. Thompson, who directs the MPC. The microbatteries are built up over several hours in an electron sputtering machine, depositing onto a silicon wafer substrate layers of current collector anodes and cathodes (usually titanium or platinum), silicon for the anode, lithium phosphorus oxynitride (LiPON) for the electrolyte, lithium cobalt oxide for the cathode, and a coating of titanium to prevent the LiPON from reacting with oxygen in air. The material is about 1 micron, or 1,000 nanometers, thick.
“What we’re really trying to achieve is high energy density, high energy capacity and reusability,” Kini says. “If you have a lot of energy that’s great, but if it’s reusable it’s even better. What we’re trying to see is: can we reuse this for 50 cycles, 100 cycles. ... If we can stack all these thin films, then we are going to have a huge energy capacity, a huge voltage. What we’re really looking at is reliability over the long term.”
Exploring solar alternatives
Sarah Arveson studied methyl ammonium lead bromide thin films in the lab of William Tisdale, an assistant professor of chemical engineering. Arveson experimented with different thin film synthesis techniques, varying thickness and temperature, comparing spin coating with drop casting, and working in a nitrogen-filled glove box. Spin coating at 1,500 rotations per minute causes the solvent to evaporate more quickly and produces thin, uniform films. She also made scanning electron microscope images of the perovskite films, which form into cubic crystals at room temperature and pressure, and saw a mix of cubic and tetragonal phases. The tetragonal phase is more stretched in one direction.
Arveson also experimented with hybrid films doped with iodine. “Instead of three bromine molecules, there will be two iodine or one iodine,” she explains. The iodine could cause different optical or structural properties in the crystal. The methyl ammonium lead bromide thin films with their perovskite crystal structure show potential for high-efficiency solar cells. “They’re inorganic-organic hybrid molecules, so the inorganic gives you very high charge carrier mobility, while the organic part gives you malleability. It’s very soft and flexible,” Arveson explains.
Forming hollow fibers
Karen Diaz Toledo, working under Professor Yoel Fink, director of the Research Laboratory of Electronics, made thin films from polycaprolactone polymer pellets, winding several layers around a hollow rod to a diameter of about 30 millimeters. The rolls are drawn into hollow fibers and could be used for drug delivery or cell transport.
Attaching quantum dots
John Lee, working with graduate student Noémie-Manuelle Dorval Courchesne in the lab of Paula Hammond, the David H. Koch Professor in Engineering and a professor of chemical engineering, studied the use of virus-based quantum dot nanowires for solar cell applications. Lead sulfide (PbS) quantum dots are dissolved in water, where they are attached to bacteriophages. "We're trying to make quantum dots that are positively charged because the bacteriophage is negatively charged, and we want to assemble them with electrostatic interaction," Courchesne explains.
"I've been learning a lot because I don't have much background in these type of ligand exchange studies," Lee says. "In order to make this happen, you have to be very knowledgeable in how ligands work. We are trying to use the (bacterio)phages and the quantum dots, so we can hopefully see a improvement in the efficiency of the solar cell."
Fighting canister corrosion
Jessica Ma undertook the study of corrosion in nuclear fuel canisters under Ron Ballinger, a professor of nuclear science and engineering. She used a coordinate measurement machine to map the surface of a sample block at 3,000 different points to provide a baseline for comparison in corrosion studies of nuclear fuel canisters. Ma studied stress analysis of the nuclear canisters and helped to create a model for calculating residual stress on the surface.
Understanding oxide catalysis
Working under mechanical engineering professor Yang Shao-Horn, Alyssa Johnson explored how to catalyze the oxygen evolution reaction in various oxide films, measuring the applied potential to electrodes for 20 different oxides, including lanthanum strontium cobalt oxide. Johnson worked with carbon electrodes, processing them in measuring resistance with rotating disc electroanalysis. "We're looking at the materials for fuel cell applications," Johnson says.
The process begins with making an ink that combines the oxide powder with carbon and applying it to the electrode so it will bind well to the surface. "Once I bind it with certain chemicals, I can deposit it onto the surface of the electrode," she explains. The electrode is then heated in the furnace for a minute and dropped into potassium hydroxide electrolyte for analysis.
"We're going to look at a cyclic voltammetry chart to see what happens when we apply a potential. That will tell us how good these materials are for the oxygen evolution reaction," Johnson says.
Probing carbon nanocomposites
Naomi Morales Medina used an X-ray diffraction system to analyze the structure of nanocomposite carbon materials and search for defects. Such materials are fabricated in industry for aeronautics and defense. Morales worked under Brian Wardle, an associate professor of aeronautics and astronautics.
The material, comprised of phenolic resin and carbon nanotubes, is heated to 1,000 degrees Celsius in the device and examined with X-rays to reveal its crystal structure. "With this in situ technique, I'm reaching temperatures of 600, 800, 1,000 degrees for my sample. The purpose of applying so much heat is just to know about the defects of the sample. Using this we have real nice results. This work will be eventually for publication," Morales says.
Seeking graphene bandgap
Gabriel Denham undertook a computational analysis of adding an amide found in nature to graphene as a way to coax an electronic bandgap in graphene. Working under Professor Markus Buehler, head of the Department of Civil and Environmental Engineering, Denham used density functional theory and molecular dynamics software to analyze the potential for applications in electronics.
"Both boron nitride and graphene are potential candidates for high-powered semiconductors that could potentially replace silicon, but ... graphene has no bandgap and boron nitride has too large a bandgap to be actually used for those applications right now," Denham says. "We're taking a bio-binder, which is a really fancy way of saying it's this molecule that's found in pig manure, so it's completely natural, and what we're interested in is particularly the amide portion of this bio-binder, that exhibits a really large delocalization of electrons. We're hoping that by putting it close to either graphene or boron nitride, we'll see some sort of electronic reaction between the two and either the creation of a bandgap in graphene or the reduction of the bandgap in boron nitride."
Controlling hydrogel defects
Julia Zhao worked with postdoc associate Mingjiang Zhong exploring defects in hydrogels with potential applications, such as an extracellular matrix. "The basic idea is trying to quantify the primary loop reactions in relation to the mechanical properties of a gel (hydrogels)," Zhao says of the joint project under assistant professors Brad Olsen, chemical engineering, and Jeremiah Johnson, chemistry.
"The challenge of this project is in most gels or elastomers you always end up with some primary loop, which is a defect in the gel," Zhong says. "The goal is to control the number of defects and also to improve mechanical properties."
Making conductive hydrogels
Eric Bailey synthesized composite hydrogel materials of carbon nanotubes embedded in a polymer, working in the lab of Professor Cullen Buie, an assistant professor of mechanical engineering.
"We'd like it to be a network of carbon nanotubes, so that gives it conductivity," Bailey says. The hydrogels are about 10 microns thick.
Measuring cartilage changes
Kayla Robinson focused on high and low glucose concentrations and their effect on cartilage. Robinson conducted one experiment for eight days and another for 22 days under the guidance of Alan Grodzinsky, a professor of biological, mechanical and electrical engineering, and the director of MIT’s Center for Biomedical Engineering. "The eight-day we have four conditions, high glucose, low glucose, then high glucose with IL 1 (interleukin-1beta protein) and low glucose with IL 1."
Studying changes in cartilage from the knee joint of cows, Robinson measured the release of glycoaminoglycan (GAG), a sugar-like molecule, released from the (IL-1) protein.
Processing carbon dioxide
Catherine Groschner explored bimetallic catalysts for turning carbon dioxide into carbon monoxide for synthesis gas, which could then be transformed into transportation fuels. Working under assistant professor of chemical engineering Fikile Brushett, Groschner used galvanic replacement reactions to modify copper foils and tested their effectiveness at carbon dioxide reduction.
Groschner studied the effect of varying the elemental composition and surface structure of copper foils via the addition of different ad-atoms with a goal of improving catalytic performance. "We're trying to make something here that's a lot of trial and error," Groschner says. "It's all brand new, I've never done any sort of electrochemistry before, and particularly not catalysis."
Catalyzing chemical intermediate
Kevin Romero evaluated water-based catalytic conditions to make a specific molecule that is an intermediate in production of certain pharmaceuticals and herbicides. Working under assistant professor of chemical engineering Yuriy Roman, Romero says, "We have a couple of catalysts that we're testing, and we're testing different reaction conditions."
Romero looked at different amounts of water, with the different catalysts, to try to make the most efficient synthesis possible. After carefully measuring and mixing the chemical ingredients, Romero puts the solution in a metal reactor chamber. The air is flushed out of the chamber with an inert gas three times, then heated to 160 degrees Celsius at about 20 times the pressure of earth's atmosphere. "It's pretty high pressure, which is why the reactor is as intense as it looks," Romero says.
The Summer Scholars presented their research at a poster session on Aug. 7.
