(807c) 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.