Dynamics and Self-assembly of Single and Multi-component Polymeric Flows: A Mesoscopic Computational Study

The focus of this dissertation is on the development of computational models to elucidate the underlying physics of single- and multi- component polymeric fluids in equilibrium and non-equilibrium settings.

I have utilized a combination of a dissipative particle dynamics methodology and an entanglement network analysis algorithm, the so-called “Z1” code, to examine the relaxation mechanisms, their corresponding time scales and single chain dynamics of moderately entangled, linear, monodisperse polymer melts undergoing simple shear flow. In so doing, not only the fidelity of the DPD methodology for entangled polymeric melts at equilibrium and under flow has been examined for the first time, but also, the intricate relationship between single chain dynamics and chain relaxation mechanisms are elaborated. Specifically, it is shown that three main time scales, τ_R (Rouse), τ_d (disengagement), and τ_rot (rotation) are the dominant relaxation mechanisms at three distinct flow regimes.

In turn, the molecular origin of shear banding in unidirectional flow of entangled polymeric melts is investigated for the first time. It is revealed that the temporal evolution of shear banding is a very sensitive function of the time scale over which the deformation rate is imposed. It is demonstrated that the stress overshoot locally inhomogeneous chain deformation and thus spatially inhomogeneous chain disentanglement. Furthermore, the localized jump in entanglement density results in a considerable jump in first normal stress and viscosity leading to the incipient shear banding. The stability of the incipient shear banded structures is studied via interfacial stability analyses.

Finally, we applied a 3D self-consistent-field theory simulations to determine the equilibrium morphologies formed by ABC triblock copolymer melts confined between two parallel plates. The main goal is the determination of conditions under which the perpendicular lamella and cylinder is stabilized; since these structures play a central role in many nanotechnology applications. To this end, the chain architecture, surface energy, and film thickness are varied to find the rational process conditions to stabilize the aforementioned morphologies. Specifically, it is shown that the perpendicular lamella and cylinder morphology is stabilized if both confined walls attract the middle block and the surface energy is large.