Speeding Up the Process

Innovative computer simulations promise to streamline the development and manufacturing of materials for consumer products — from plastics to batteries to electronics.

For Sitaraman Krishnan, solving a practical problem, while discovering something new, motivates him to pursue his research.

Sitaraman Krishnan

“My students and I like to investigate properties of complex and novel materials and understand how they conform to known laws of physics,” he says.

Krishnan, an associate professor of chemical and biomolecular engineering, is working to reduce the synthesis time and cost for various types of polymers. Polymers are compounds consisting of many repeating structural units that are bonded together. They are used as the starting material for many consumer products, such as plastic and nylon.

“If we can predict the properties of these materials even before we synthesize and characterize them, we can choose to only work on materials that have potentially useful properties,” he says.

Predicting the mechanical properties of polymers remains a challenge because current analysis methods often yield results that significantly differ from experimental measurements. Krishnan’s own experiments have shown that these values can differ by at least 700 times.

To tackle this challenge, he uses pi-conjugated polymers as his model materials. These polymer structures consist of alternating double and single bonds, with “delocalized” electrons moving throughout the polymer chain. The moving electrons give these polymers the ability to conduct current. One example is poly (para-phenylene vinylene), better known as PPV, which is used to manufacture displays for cell phones and TVs.

Krishnan designs computer programs to simulate how atoms in a polymer interact with one another according to Newton's laws of motion. These simulations enable him to predict the properties of that polymer and determine if it is feasible to synthesize. Harnessing advanced computing capabilities, he can perform these simulations efficiently using common desktop computers.

Our results confirm that we can predict the properties of new polymers,” he says. “That means we can now screen materials for potential use in specific applications using the computer even before we synthesize them, leading to significant savings in efforts and costs.

Sitaraman KrishnanSEM (scanning electron microsope) images of polymer-coated carbon nanotubes. Photos: Arvind Sreeram, graduate student.
SEM (scanning electron microsope) images of polymer-coated carbon nanotubes. Photos: Arvind Sreeram, graduate student.

In a recent study, Krishnan was able to successfully predict the elastic modulus and glass transition temperature of a polymer. The former is important for polymers used in products such as textiles and artificial skins, in which crumpling may occur. The latter is a threshold above or below which the polymer texture changes significantly. “These parameters are basic properties that determine the mechanical behavior of a polymer,” he explains.

Not only did he predict the values for these properties, but he also synthesized the polymer of interest and showed that the experimental measurements coincide with his predicted values.

“Our results confirm that we can predict the properties of new polymers,” he says. “That means we can now screen materials for potential use in specific applications using the computer even before we synthesize them, leading to significant savings in efforts and costs.”

Krishnan has since used his simulation programs to predict other polymer properties that are also crucial to synthesis, such as densities and thermal extension coefficients. His next step is to understand how polymers behave at different temperatures so that he can better predict their properties.

Krishnan is also using his knowledge in polymer properties to create novel methods for synthesizing polymers, specifically those that can conduct electricity. He has built strong ties with industry partners and hopes that his research can lead to more efficient manufacturing processes for energy storage devices.

“I want to demonstrate the use of the materials we have developed in my lab in practical devices, such as supercapacitors, solar cells and lithium ion batteries,” he says.

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