University of Minnesota
School of Physics & Astronomy

Spotlight

Coarse-grain modeling of polymers

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Physicists at the School of Physics and Astronomy are using modeling techniques to make things easier for chemists working with polymers. Taher Ghasimakbari is a graduate student working in theoretical condensed matter physics on diblock copolymers, a family of materials with wide range of applications from drug delivery to strengthening plastics. Spandex and polyurethane are examples of block copolymers in the same family of materials as diblock copolymers ever since. This class of polymers were invented in the 1950s and have been studied extensively.

However, there has been difficulties in applying computational techniques to predict experimental results due to complicated nature of diblock copolymers. Ghasimakbari recently contributed in establishing a method that will bridge between simulation and experiment. "Trial synthesis of diblock copolymers aimed for different properties can be very tedious and overwhelming due to huge number of parameters involved," Ghasimakbari says. "Trying different substances under different conditions is not just expensive but also is very time-consuming, so predicting the effect of different parameters using simulations will be a tremendous help for experimentalists."

A family of polymers composed of two distinct homopolymers connected covalently head to tail are called diblock copolymer. Atomic level simulations of diblock copolymers are limited to very tiny systems with maximum of few hundred particles due to computational limitations. However, coarse grain modeling makes it possible to study physical properties at larger length scales by encapsulating the chemical details into a few effective parameters. Ghasimakbari is hoping to map the entire phase diagram of diblock copolymers using his coarse-grained simulations. Diblock copolymers with different chemistry show similar behaviors on length scales comparable to polymer length, which is known as the hypothesis of universality. "The phase separation and structure formation is an example of universal behavior observed among diblock copolymers polymers. This phenomenon and many others can be explained with very few coarse-grained parameters containing relevant chemical details," he says.

Ghasimakbari's work will be tested by experiments performed in the Chemical Engineering Dept of the University of Minnesota which is an ongoing project. "Experimental results from Bates group in the Chemical Engineering Dept have shown good agreement with simulation results on symmetric diblock copolymers, but there is still a lot to do!" In the next step Ghasimakbari’s research will be focusing on dynamics and thermodynamics of asymmetric diblock copolymers. "There are many applications for diblocks. Coming up with tool for engineering their behavior before synthesizing them would be a great advantage."