(413d) Extracting Fundamental Materials Properties From Rheological Measurements

Extracting
Fundamental Materials properties from Rheological Measurements

Folarin
Latinwo¹
and Charles M. Schroeder¹

¹Department
of Chemical & Biomolecular Engineering, University of Illinois at
Urbana-Champaign, Urbana, IL 61801

A long
standing problem in complex fluids has been the determination of
fundamental materials properties (e.g. elasticity) from dynamic
far-from-equilibrium measurements (e.g. transient stresses). We
recently developed a framework to extract information about polymer
elasticity from trajectories of conformational changes of single
molecules induced by fluid flow [1]. In our approach, we applied
tools from non-equilibrium statistical mechanics namely the Jarzynski
relation [2] to
complex fluids via
Brownian dynamics (BD) simulations of bead-spring models of polymer
molecules. The relation allows for the calculation of free energy
changes from work distributions of arbitrarily far-from-equilibrium
processes and has been applied as
originally conceived only
to single molecule studies. In our current work, we demonstrate the
further application of this new tool to complex fluids by
determination of free energy changes from transient bulk stresses.
Using BD simulations of bead-spring models of dsDNA and polystyrene
molecules in various flow types (shear and extensional) and standard
expressions for the stress tensor (e.g. Kramers-Kirkwood), we make a
connection between stresses, work distributions of bulk measurements
and the Jarzynski relation. In doing this, we developed a formalism
to extract new fundamental information such as free energies (which
intrinsically defines a system) from previously existing
measurements.

[1]
Latinwo,
F. and Schroeder, C. M. Physical Review Letters, submitted.

[2]
Jarzynski,
C. Phys. Rev. Lett. 78, 2690--2693 (1997).