(455b) Extended Flory-Huggins Model for Poly-(ethylene) Oxide Solutions

Extended Flory-Huggins model for poly-(ethylene)
oxide solutions

M. I. Chaudhari, L. R. Pratt

Tulane University, New Orleans, LA 70118

            Classic Flory-Huggins model for polymer
phase equilibria is based on a lattice model and widely used to understand thermodynamics
of polymer solutions. Nevertheless, this model is only applicable to polymer
solutions that are sufficiently similar components. Bae et.al. (1993) showed
that this model is unsatisfactory for aqueous poly-(ethylene) oxide solutions
(FIG 1). Composition independence of interaction parameter and assumption of
zero volume of mixing is often inadequate for such systems. Here, we present
extended Flory-Huggins model based on evaluation of the activity of the small
molecular solvent (water). 
Molecular simulations of poly-(ethylene) oxide
chains molecules capped with small hydrophobic groups solvated with water are
analyzed for generating solution structure information required for extended
model. We will survey the structural information that is a basis for a recent
proposal for high-angle neutron scattering for these solutions. Then we present
the computed solvent activities, and the implied Flory-Huggins interaction
parameter (X) are presented.
Our aim is to validate this extended model by molecular dynamic simulation and
understand thermodynamics of these PEO polymers in solutions.

FIG.
1: Composition
dependence of the Flory-Huggins interaction parameter interred from the data of
reference below for the PEG/water system for two temperatures. ¯₁ is
the volume fraction of the small-molecule solvent. Assumption of composition
independence of X₁₂ is less satisfactory for
PEG/water system. The temperature dependence is is stronger, and thus clearer,
for this system, and the interaction strength increases with increasing
temperature, reflecting significant entropic contribution.

1.
Bae, Y.C., Shim, J.J., Soane, D.S., and Prausnitz, J.M., J. App. Poly, Sci., 47, 1193-1206(1993)