(4eq) Computational and Theoretical Studies of Polymer Self-Assembly

Block copolymers can self-assemble into various periodic structures ranging from simple phases like lamellae, cylinders, etc. to more complex phases like Frank-Kasper phases. These structures find their applications in drug delivery, filtration, structure-directing agents, and nanolithography as a few examples. Due to advancements in synthetic chemistry over decades, today block copolymers can potentially be designed in many architectures giving us a tremendous opportunity to tune the target structure thereby tuning the material's properties. Motivated by their applications and my curiosity to go beyond simple block copolymers, my future independent research will use computational simulation in conjunction with theoretical tools to explore the design space of these molecules and understand the self-assembly processes. The simulation methods will include dissipative particle dynamics, Kremer-Grest bead-spring model, vertex model along with self-consistent field theory as a theoretical tool. My initial research topics are:

1. Developing the phase diagram of linear and cyclic block copolymer blends. Although these two architectures are widely studied, there is little to no information on the self-assembly of these blends, especially, in the region of Frank-Kasper phases. The knowledge of blending to manipulate phases can be an effective strategy to manipulate the target structures and control their properties.
2. Estimation of Flory-Huggins chi parameter as a function of block copolymer architecture. For a chosen chemistry of monomers, the effective chi parameter largely depends on the polymer architecture. The empirical relationship between the chi parameter and the chain architecture will be a guide for experimentalists to obtain a desired ordered phase for a given block copolymer.
3. Thin film self-assembly of knotted block copolymers. Knots on the polymer chains affect the dynamics and the final equilibrium structures. Motivated by nanolithography, the molecular assembly of such systems in a thin film environment will be investigated.

Research Experience

Graduate Student, Department of Chemical and Biomolecular Engineering, Tulane University; Prof. Julie Albert and Prof. Hank Ashbaugh

Throughout my Ph.D., I have developed a keen interest in polymer physics by working on different aspects of polymeric systems. In my first project, I studied binary blends of diblock copolymers (linear/linear or linear/cyclic) where I found that a polymer size mismatch between the blend components is positively correlated with the segregation strength of the blend at the order-disorder transition (ODT) and explain this curious behavior in terms of mismatch in characteristic lengths of polymer domains in the disordered phase near the ODT. In another project, I examined block copolymer thin films by incorporating surface interactions. Here, I find that the formation of vertical lamellae in a thin film of linear diblock copolymers is more robust compared to that formed by the analogous cyclic chains (equal molecular weight or twice the molecular weight of linear polymer) and explain the discrepancy in terms of near-substrate chain orientations. I also led a project where I investigated the interfacial properties of block random copolymers (A-b-(B-r-C)) with an emphasis on designing a rule to predict the surface energy of random coblock in the lamellae and comparing that with the mean-filed prediction. The work was in collaboration with Prof. Whitney Loo at the University of Wisconsin. These problems have direct applications in nanolithography.

Postdoctoral researcher, Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute; Prof. Patrick Underhill

Understanding the assembly states of soft particle domains by using the Vertex model. Coarse-grained simulations of soft particles involving pair-wise interactions are speculated to have limitations in predicting the minimum free energy states. Further, the understanding of metastable states and dynamic pathways is restricted due to the unaffordable computational cost of the simulations. My postdoctoral research focuses on tackling such issues by utilizing a novel theoretical and less expensive computational approach namely the Vertex Model to simulate soft particles where the energies are effectively not pair-additive. This model has been shown to capture the ODT in soft particles assembly. We aim to develop a phase diagram for such particles based on two parameters: the energy associated with the surface area of the particles and the energetic cost of changing the particle volume.

Teaching Interests:

My formal undergraduate program, PhD training, and postdoctoral work in a chemical engineering department have given me proficiency in fundamental chemical engineering concepts and a unique viewpoint on interacting with students from a variety of backgrounds and interests. I would like to teach a range of subjects, including thermodynamics, statistical mechanics, reaction kinetics, numerical methods, and polymer science and engineering. During my PhD, I have also worked as a teaching assistant for two courses: Numerical Methods and Unit Operation Lab. Over the past five years, I have mentored various undergraduate and graduate students on their research and the experience has been largely satisfying to me. I am also eager to work on science outreach projects outside my focused research area.