Abstract
Phase diagrams for aqueous poly(ethylene glycol) (PEG)-(NH 4) 2SO 4 two-phase systems with PEGs of different molecular weights from 300 to 20,000 were determined by the measurements of the salt and PEG concentrations in the phases. Partition coefficients for a homologous series of sodium salts of dinitrophenylated (DNP-) amino acids with aliphatic side-chains were studied in the systems as functions of the systems composition. The free energy of transfer of a CH 2 group from one phase to the other in the systems was estimated and used as a measure of the difference in the relative hydrophobicity of the phases. The results show that the difference in the relative hydrophobicity of the phases in the aqueous PEG-(NH 4) 2SO 4 systems is governed mainly by the difference in the PEG concentrations between the phases. The difference in the ability of water in the phases to participate in electrostatic ion-dipole interactions estimated using the logarithm of the partition coefficient of sodium salt of DNP-glycine as a measure was found to be governed mainly by the difference in the salt concentrations between the phases. The results obtained imply that phase separation and physicochemical properties of the phases of the aqueous PEG-salt systems are governed by the mechanisms similar to those typical for aqueous two-polymer systems.
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