(3dr) Molecular Simulations for Understanding Morphology At Interfaces

Understanding the morphology and packing of nano materials at interfaces and in the bulk often determines their applicability. In fact, many applications rely on preferential orientation and packing of nano-entities at the molecular level for efficient and reliable performance.^1,2Computational tools such as molecular dynamics (MD), dissipative dynamics using coarse grained models, and quantum-mechanical calculations are being increasingly employed to investigate morphological and packing features, and to complement and guide experimental efforts.

My doctoral studies involved assessing the surfactant morphology at water-solid interfaces to aid in the description of admicellar polymerization. MD simulations of the surfactants at the water-nanotube interface were performed to discuss the effect of the curvature on the adsorbed surfactant morphology, which is important for the understanding of the dispersion of nanotubes. During my postdoctoral studies at University of Oklahoma, I investigated propagation of nanoparticles through porous media using the Lagrangian tracking model and the flow field in porous media was computed from a continuum Lattice-Boltzmann model.

At the Georgia Institute of Technology, I am performing simulations to gain molecular-scale understanding of the interfacial region in bulk heterojunction photovoltaic devices made of small-molecule donors and fullerene acceptors.³ Random blends of benzothiodiazole-dithienopyrrole-benzothiadiazole (BTD-DTP-BTD),⁴a small molecule donor, and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), a commonly used acceptor, were created for this purpose and MD simulations were performed to calculate the solubility parameters and thermodynamics of these blends, and to provide a platform to perform coarse graining of these molecules. Coarse graining would potentially reveal the equilibrium molecular-scale morphologies at interfaces; then, semi-empirical quantum calculations on the snapshots obtained from MD simulations would allow to study the electronic couplings between these molecules, which in turn would be used to determine the optimal interfacial morphology.

                (1)          Kim, M.; Hohman, J. N.; Cao, Y.; Houk, K. N.; Ma, H.; Jen, A. K.-Y.; Weiss, P. S. Science 2011, 331, 1312.

                (2)          Zhang, H.; Hussain, I.; Brust, M.; Butler, M. F.; Rannard, S. P.; Cooper, A. I. Nat Mater 2005, 4, 787.

                (3)          Mishra, A.; Bäuerle, P. Angewandte Chemie International Edition 2012, 51, 2020.

                (4)          Polander, L. E.; Pandey, L.; Barlow, S.; Tiwari, S. P.; Risko, C.; Kippelen, B.; Brédas, J.-L.; Marder, S. R. The Journal of Physical Chemistry C 2011, 115, 23149.