Reversible Switching of Adhesion With Polyelectrolyte Brushes Via Uptake and Release of Multi-Valent Ions

“Reversible switching of adhesion with polyelectrolyte brushes via uptake and release of multi-valent ions”

 

 

Abstract:

 

Polyelectrolyte brushes represent a large portion of polyelectrolyte applications, but also provide an excellent system for studying the behavior and physical properties of polyelectrolyte chains in solution.  Polyelectrolyte ‘brushes' consist of charged polymer chains extended outward into solution with one end tethered to an interface.  The applications of end-tethered polyelectrolyte brushes once primarily revolved around their colloidal stabilization and low frictional properties, but now represent a much wider range of possible applications including materials for coatings and adhesives, drug and therapeutic delivery, biological interactions, and energy storage.

This work explores the responsive and reversible nature that polyelectrolyte brush chains exhibit when interacting with oppositely charged multi-valent ions and complexes.  Other studies with responsive polyelectrolyte materials have mostly centered investigations on temperature, pH, or mono-valent salt effects.  However, previous work has left an important hole in the stimuli-responsive polyelectrolyte literature regarding polyelectrolyte interactions with multi-valent entities; which produce tremendous physical property changes.  When polyelectrolyte brushes contain tri-valent lanthanum counterions, for example, adhesion measured upon separating two brushes has been measured at as high as 30 mN/m (almost half the surface tension of water with respect to air, 72 mN/m).  Furthermore, this adhesion has been observed to reversibly appear and disappear upon the uptake and release, respectively, of multi-valent counterions.  This reversible transition also corresponds to changes in polyelectrolyte chain length, as can be observed below.