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Electrostatic and Excluded Volume Effects on the Transport of Electrolytes in Poly(ethylene glycol)-Water "Mixed Solvents"

Summary: Electrostatic and Excluded Volume Effects on the Transport of Electrolytes in
Poly(ethylene glycol)-Water "Mixed Solvents"
Fabio Capuano, Alessandro Vergara, Luigi Paduano, Onofrio Annunziata, and
Roberto Sartorio*,
Dipartimento di Chimica, UniVersita` di Napoli "Federico II", Monte S. Angelo, Via Cinthia,
80126, Naples, Italy, and Center for Materials Science and Engineering, Massachusetts Institute of Technology,
77 Massachusetts AVenue, Cambridge, Massachusetts 02139
ReceiVed: January 28, 2003; In Final Form: July 29, 2003
The transport properties of NaCl in poly(ethylene glycol)-water (PEG-water) mixtures are presented, with
special regard to the dielectric and hydrodynamic effects. We report experimental data of mutual diffusion,
viscosity, and conductivity for the aqueous ternary system containing PEG with an average molecular weight
of 2000 a.m.u. (PEG2000, component 1) and sodium chloride (NaCl, component 2). Both PEG2000 and
NaCl are used extensively as protein-crystallizing agents. The four diffusion coefficients (D11, D12, D21, and
D22) that are required to describe the diffusive properties of a ternary system correctly were determined by
the precise Gouy interferometric method. We also report measurements of the dielectric constant for several
aqueous binary systems containing PEG with three different molecular weights (200, 400, and 2000 a.m.u.),
which significantly decreases the dielectric constant of aqueous solutions. The experimental values of the
four diffusion coefficients are discussed in terms of obstruction, excluded volume, and dielectric effects. The
dependence of the PEG main-term diffusion coefficient, D11, on the salt concentration is quantitatively described
by the corresponding change of viscosity. The cross-term diffusion coefficients, D12 and D21, are described


Source: Annunziata, Onofrio - Department of Chemistry, Texas Christian University


Collections: Chemistry