Structure, Dynamics and Rheology of Polymer Solutions from Coarse-Grained Molecular Dynamics: Effects of Polymer Concentration, Solvent Quality and Geometric Confinement

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

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biomedical and Chemical Engineering

Year

2015

Author dc:creator

• Yang, Yutian

Contributors dc:contributor

• Radhakrishna Sureshkumar

• Engineering

Repository record dc:identifier

https://surface.syr.edu/etd/416

OAI identifier oai:identifier

oai:surface.syr.edu:etd-1416