Effect of ionic strength and ionic species on partitioning behavior of hydrophobic and hydrophilic polystyrene latex beads in aqueous two-phase polymer systems

Brian C. Tripp, Eric W. Kaler, Stanley I. Sandler, Alex Kopatsis

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

The effects of ion type, pH, ionic strength and colloidal surface properties on the partitioning of three different types of polystyrene latex beads with different surface properties in the two-phase polyethylene glycol (PEG)/dextran (DEX) system have been measured. Certain inorganic monovalent ion types alter the partitioning of hydrophilic polystyrene beads from the top PEG-rich phase to the bottom DEX-rich phase, while hydrophobic polystyrene beads always partition into the top PEG-rich phase, regardless of the type and concentration of salt. The partitioning of the hydrophilic beads depends on the ionic strength as well as the ion type, and is not due to changes in pH. Strong water-structure-making sails, e.g. ammonium sulfate, are least likely to induce partitioning to the bottom phase, while sodium azide, a pseudo halide, has the strongest effect on partitioning of the beads. The Hofmeister series does not predict the relative effectiveness of the different ions that do alter the partitioning of the hydrophilic beads. The polyacrylic acid (PAA) coating on the hydrophilic beads is known to strongly interact with PEG and polyoxyethylene (PEG) polymers, via hydrogen bonding, especially at lower pH values. This strong polymer-polymer interaction may be disrupted by many salts, e.g. sodium chloride, at higher ionic strengths. In general, the influence of ions on the conformation, solvation and free energy of PEG in aqueous solution, and its interaction with PAA, is a complex phenomenon and is not predicted by existing theories. Depletion flocculation may also play a role in the salt-dependent bead partitioning behavior. A general consequence of the acid-PEG interaction is that relatively hydrophilic solutes with many surface carboxylic acid groups may partition to the top PEG-rich phase, even though it is the less polar of the two phases in the PEG/DEX system. This phenomenon may explain the partitioning behavior as a function of salt observed for certain species of bacteria.

Original languageEnglish (US)
Pages (from-to)151-164
Number of pages14
JournalColloids and Surfaces B: Biointerfaces
Volume6
Issue number3
DOIs
StatePublished - Apr 2 1996

Keywords

  • Dextran
  • Partitioning behavior
  • Polyethylene glycol
  • Polymer systems
  • Polystyrene latex beads
  • Surface properties
  • Two-phase

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