Seminar: Specific Ion Effects in Polymer Brushes

  • Date: –14:00
  • Location: Biomedicinskt centrum, BMC room C2:305
  • Lecturer: Professor Erica J. Wanless, The University of Newcastle, Australia
  • Organiser: Department of Pharmacy
  • Contact person: Randi Nordström
  • Seminarium

Polymer brush coatings are an effective means to modify the surface of an object and thus change the nature of the interaction of the object with its surrounding environment. The conformation of a terminally anchored polymer brush will change in response to the quality of its solvent environment. Factors that can drive a change in the conformation of a brush include the polymer hydrophobicity or charge. The impact of conformational changes can include alteration of the brush surface wettability, adhesion or friction. Such changes can be controlled reversibly in aqueous environments for weak polyelectrolytes through a change in the solution pH, or for a thermoresponsive polymer through a change in the temperature.

What is less commonly reported, is that many, if not all of these systems display an additional response to electrolyte ionic strength and indeed the identity of the constituent ions. Widely known as either specific ion or Hofmeister effects, the response of a polymer brush varies in the presence of different ions. We have deployed a powerful combination of physical characterisation tools in our efforts to understand the nature of these variations in aqueous environments. This includes ellipsometry, quartz crystal microbalance with dissipation, atomic force microscopy, contact angle and neutron reflectometry measurements. Together these yield information about the brush thickness, surface characteristics and depth profile.

Examples of specific ion effects for both weakly basic tertiary amine methacrylate brushes (pH and salt responsive),[1-2] and the thermoresponsive poly(N-isopropylacrylamide),[3-4] and poly oligo(ethylene glycol methacrylates),[5-6] will be presented.

The strong influence of ion identity on polymer brush behaviour is an area of ongoing investigation in our research group and impacts all potential applications of polymer brush coatings.