Date of Award
December 2015
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biomedical and Chemical Engineering
Advisor(s)
Radhakrishna Sureshkumar
Subject Categories
Engineering
Abstract
Understanding flow-microstructure interactions in macromolecular fluids is of great
importance in the design and optimization of ubiquitous polymer processing operations.
Further, such interactions are routinely encountered in separation of biopolymer mixtures
using gel electrophoresis and microfluidic technologies, manufacturing of polymer-based
functional nanocomposites and polymer-induced reduction in turbulent friction drag. To
date, the vast amount of theoretical/computational modeling efforts on flowmicrostructure
coupling has focused on continuum-level and stochastic descriptions.
Such approaches, while useful in qualitatively predicting polymer dynamics and rheology
in model systems, are incapable of describing the effects of polymer-solvent, polymerpolymer
and polymer-wall interactions. Further, in the context of polymer solutions, the
incorporation of hydrodynamic interaction are often computationally challenging. Hence,
the goal of this work has been to investigate the structure, dynamics and rheology of
solutions of flexible linear polymers using molecular dynamics (MD) simulations in
presence of explicit solvent mediated interactions.
Coarse-grained (CG) molecular models and corresponding force fields are employed
to describe the polymer, solvent and the underlying physico-chemical interactions. The
CG models are validated against atomistic ones by comparing the predictions of certain
structure parameters such as persistence length, radius of gyration and radial distribution
functions of the monomeric units. Results are first presented for the dynamics of a single
polymer chain in shear flow. The effects of chain length and shear rate on the
configuration statistics, e.g. tumbling frequency and orientation distribution of the end-toend
vector, are presented and compared to experimental observations as well as
predictions of mesoscopic stochastic dynamic theories. Further, the effects of solventpolymer
interactions on the configuration dynamics of a single polymer chain under
good, theta and poor solvent conditions are discussed. Specifically, the role of solvent
quality is shown to have a pronounced effect on coil-stretch transition in shear flow. We
also show that in addition to tumbling dynamics, polymer chain may undergo
configurational changes through a novel mechanism, namely collapse dynamics. CGMD
predictions for the relationship between the zero-shear viscosity and polymer
concentration in dilute and semi-dilute regimes are presented and compared to
experiment results. Shear thinning behavior is observed in both dilute and semidilute
solutions in non-equilibrium molecular dynamics simulations. Possible approaches to
parameterizing phenomenological constitutive models using MD simulation data is
explored. Subsequently, influence of solvent quality on the rheological properties of
dilute and semidilute solutions is discussed. Finally, the effect of geometric confinement
on equilibrium configurations as well as shear-induced migration of the polymer chains is
described.
Access
Open Access
Recommended Citation
Yang, Yutian, "Structure, Dynamics and Rheology of Polymer Solutions from Coarse-Grained Molecular Dynamics: Effects of Polymer Concentration, Solvent Quality and Geometric Confinement" (2015). Dissertations - ALL. 416.
https://surface.syr.edu/etd/416
