Conformation and Rheology of Semiflexible Macromolecules Using Non-Equilibrium Brownian Dynamics and Monte Carlo Simulations
Andrews, Naveen Chandy
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https://hdl.handle.net/2142/82437
Description
Title
Conformation and Rheology of Semiflexible Macromolecules Using Non-Equilibrium Brownian Dynamics and Monte Carlo Simulations
Author(s)
Andrews, Naveen Chandy
Issue Date
1997
Doctoral Committee Chair(s)
McHugh, A.J.
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Language
eng
Abstract
Non-Equilibrium Brownian Dynamics Simulations (NEBD) and Configuration-Biased Monte Carlo (CBMC) methods are used to model the dynamics of semi-flexible macromolecules and polyelectrolytes undergoing shear and extensional flow. The mathematical model utilizes a discretized version of the Kratky-Porod wormlike (or persistent) chain as the building block, generalized to include flow. This discrete chain contains beads which interact through stretching and bending forces, and for polyelectrolytes a screened Debye-Huckel potential is also present. The Fokker-Planck equation describing this chain is converted to a Stochastic Differential Equation (SDE) from which the simulation algorithm for the NEBD is obtained. In steady, potential flows, the solution of the Fokker-Planck equation exists and is used in the generation of trial and acceptance moves in the CBMC scheme. Various conformational and rheological quantities are monitored, under both steady-state and transient conditions, with the primary independent variables being the $flexibility\ parameter\ \beta ,$ the bending constant of the chain, and for polyelectrolytes, the salt concentration (parametrized through the Debye length) and the strength of interaction q, related to the degree of ionization of the chain. The model qualitatively describes many of the experimentally-observed effects in such systems, most notably birefringence overshoots, cessation effects, and various steady-state effects. The crucial advantage of the NEBD over an analytical treatment is its ability to incorporate (analytically intractable) effects such as hydrodynamic interactions and its (natural) ability to obtain transient information, a facet useful in comprehending the differing dynamics of molecules of varying rigidity. In addition, excluded volume effects on transient orientational and rheological behavior is studied.
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