March 26, 2013

The Scientist: Prof. Lynden Archer Researches Polymers

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Prof. Lynden Archer, director of chemical and biomolecular engineering, has always been enamored by polymers.

“I remember, as an undergraduate, deciding to do polymers in my first semester because the person who taught me my first chemical engineering course was a polymer scientist, and he had so much fun making polymers,” Archer said.

Archer went on to obtain his bachelor of science degree in polymer science in 1989. This was the period right after the oil embargo in the U.S. – something that led to him having a strong awareness about being smart in using scarce oil resources.

“If you were going to use those resources to make materials, you wanted to make the best polymer material possible and this caught my imagination,” he said. Archer has stuck to working on polymers ever since.

The basic push of his research is to synthesize and study polymers which are chemically attached to surfaces such as silicon or germanium.

According to Archer, the motivation for his work came from the fact that although pure polymers can be designed for any application, and their behavior is well understood, the interactions between polymers and a surface or substrate is not well studied even though such interactions are common in nature.

Archer’s research group studies polymers attached to a 1-D point in order to make branched structures, a 2-D plane to create slippery surfaces and 3-D nanoparticles to create materials called NOHMs, or nanoscale organic hybrid materials, which can be used as electrolytes in batteries.

The synthesis of these 3-D tethered polymer materials called NOHMs is one of his lab’s largest discoveries. NOHMs are pom-pom looking hybrid structures of the best low-cost and lightweight organic polymer chains tethered to the best of inorganic nanoparticles like silicon dioxide.

The traditional way to synthesize these materials is to produce the organic and inorganic parts separately and mix them, but this does not result in a homogeneous mixture at the molecular level. Archer’s lab worked on synthesizing these materials using a bottom-up approach to ensure homogeneity at the molecular level.

Archer said his 12-year old daughter coined the term NOHMs, which she said sounds like “gnomes,” when he was struggling to come up with a catchy name for these materials.

“I like to think of NOHMs as a hybrid of hybrids, where every building block is a nanoscale hybrid,” he said. Archer’s group has since tackled various questions about the physics of the behavior of these polymers and their applications.

One interesting physical attribute of these 3-D systems is that they act like a fluid under certain conditions. According to Archer, one would expect the nanoparticle-polymer hybrid to be suspended in some kind of solvent to result in these fluid like properties, think about the various blood cells suspended in the plasma or the solvent of blood, but these hybrid materials are actually self-suspended with no solvent.

Currently, Archer is involved in making better battery systems using NOHMs.

“The lithium-ion battery systems we are enamored with today are essentially a holdover from mobile technology, it’s really no surprise when they are not as successful for cars and laptops that require more energy,” Archer said.

Every battery system has a positive terminal called a cathode; a negative terminal called an anode and a solution or electrolyte which helps ferry the electrons from the anode to the cathode through electrochemical reactions. Lithium batteries em­ploy a lithium anode which is capable of sparing one electron per atom.

One of the major problems with using metallic anodes in battery systems, Archer said, is the formation of tree like structures called dendrites upon charging and recharging the battery. These short circuit the battery, causing safety and performance issues.

According to Archer, his group is currently working on modelling these dendrite formations and designing battery electrolytes using NOHMs to provide a porous media to control the dendrite growth.

Creating better battery systems capable of storing large amounts of energy can lead to green solutions because these systems aid in storing energy produced from renewable energy sources for future use, Archer said.

“Most people tend to forget that green technology is sustainable only if it is economically viable,” Archer said.  However, according to Archer, the problem with using lithium batteries is that there is not enough lithium available in the world to reduce usage of fossil fuels by adopting batteries. Any increase in the demand for lithium for batteries will also drive up the price of lithium because of its limited availability.

Aluminum, on the other hand, is the most abundant metal in the Earth’s crust. According to Archer, aluminum has the advantages of cost, natural abundance and also has three electrons to spare compared to lithium’s one which makes it seem like the perfect solution. But aluminum also has the same dendrite problems as lithium, and the aluminum ions are bulky, which increases its shuttle time in the electrolyte.

“We are on the right path and I predict that in the next five years, aluminum will be competitive with lithium at least in cost and performance,” Archer said.

Archer is also the co-director of the King Abdullah University of Science and Technology –  Cornell Center for Energy and Sustainability. The center was set up with a $25-million grant provided over five years by KAUST and has several partner universities as its collaborators.

“The nice thing about collaboration is that there is a nice feedback loop and a dynamic exchange of knowledge in research is critical,” he said.

According to Archer, such collaborations also help focus on the applications of polymer materials, which led to the founding of a company called NOHMs Technologies in Ithaca. Archer is the founder and a technical advisor of the company.

“Without deliberately connecting our research work on the fundamental side of polymers to these applications, such businesses would not be possible,” he said. NOHMs Tech­nologies commercializes battery systems using lithium-sulphur anodes with NOHMs as a part of the electrolyte.

Until this year, Archer also taught Chemical Engineering 3230: Fluid Mechanics.

“I live the best life one could ever live because I do so many different things in any given day from interacting with students in the lab and interacting with staff as a director, but interacting with young [undergraduate] students is really special,” he said.

Even though research in chemical engineering has evolved over the years to studying systems at the molecular scale, Archer believes the old adage that “chemical engineers are glorified plumbers” still stands true.

“To understand the plumbing or the fluid mechanics of a polymer system, it is really important to study, at a fundamental level, how the polymers interact with each other and with the surfaces of the pipe, and this leads back to where it all started for me,” he said.

Original Author: Srinitya Arasanipalai

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