2016 President's Report - page 18-19

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.
by Shelia Yong
Clarkson University
19
16
President’s Report
For Sitaraman Krishnan, solving a practical
problem, while discovering something new,
motivates him to pursue his research.
“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
& 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 are significantly different
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-phenylenevinylene), better
known as PPV, which is used to manufacture displays
for mobile 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.
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, where 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 screenmaterials 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.
“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.”
— Prof. Krishnan
SEM (scanning electron
microsope) images of polymer-
coated carbon nanotubes.
Photos: Arvind Sreeram, graduate
student.
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