Date of Award

December 2015

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Biomedical and Chemical Engineering


Radhakrishna Sureshkumar

Subject Categories



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



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