(6p) Multiscale Simulations of Polymer Dynamics, Polymerization Kinetics, and Polymer Blend Morphology

The availability of fast and large mulitnode computer clusters have made computer simulations of polymers routine. Development of parallel algorithms and availability of accelerators such as graphical processing units (GPUs) further enhanced our capability in performing these simulations. Despite these advances, simulating polymeric systems still remains a challenge because of the multiscale nature of polymers that spans multiple length and time scales. To illustrate I am presenting a vignette of my latest works where I used different coarse-graining techniques and atomistic simulations to simulate: (1) the dynamics of unentangled polymer melts confined in a highly adsorbing cylindrical walls, (2) the polymerization kinetics and chain characterization of bottle-brush macromolecule synthesized through the macromonomer approach, and (3) the morphology and characterization of organic photovoltaic blends with emphasis on the structure of the donor/acceptor interface. All simulation results were qualitatively, and in some cases quantitatively, in agreement with neutron scattering experiments.

For example in the simulations of polymer melts confined in pores, we used a polymer bead-spring model to simulate anodize aluminum oxide (AAO) infiltrated with polydimethyl-siloxane (PDMS) and found excellent agreement in the dynamic and static properties of the chains between neutron spin echo (NSE) and small angle neutron scattering (SANS) experiments, respectively. In the second example, we used a bead-spring model of a macromonomer and simulated ring opening metathesis polymerization (ROMP) by sequentially adding macromoners to form bottle-brush macromolecules. The structure of the bottle-brush was compared to SANS experiments. In the third example, a hindered-rotation model of a polymer was used to model poly(3-hexylthiophene) (P3HT). The simulation results of the P3HT/PCBM blend, in the presence of a substrate, shows qualitative agreement with neutron reflectivity (NR) experiments where a vertical composition profile indicating PCBM rich regions in the vicinity of the substrate and air interfaces. Furthermore, the orientation of the thiophene rings in the donor/acceptor interface was also investigated using atomistic molecular dynamics simulations.

My objective is to perform simulations that would tackle difficult areas in polymer physics such as charged polymers, liquid crystalline polymers, polymers at interfaces and polymer crystallization. In these future works, I will actively search for areas of collaboration with the goal providing insights that will provide a better understanding of these polymeric systems. The above examples illustrate my strategy to meet the challenge.