Presentation day

wednesday  11:30 AM

TITLE

Nanostructure and stimuli-responsibiilty of poly(betaine) brushes at the air/water interface

Abstract

Polybetaines are zwitterionic and they show quite different properties from simple
polyelectrolytes, i.e., polycations and polyanions. [1,2] In this study, nanostructure and its stimuliresponsibility
of zwitterionic polybetaine brush were investigated by X-ray reflectivity (XR). The fundamental
properties of betaine polymers were also studied by dynamic light scattering (DLS), static light scattering
(SLS), and zeta-potential measurements.
Amphiphilic diblock copolymers with zwitterionic polybetaine and hydrophobic blocks were synthesized by
RAFT method. Three different betaines, i.e., carboxybetaine[3], phosphobetaine, and sulfobetaine were
used (Fig.1). The diblock copolymers were spread on the water surface to form monolayer. In the
monolayer, polybetaine brush is formed at the hydrophobic layer/ water interface. Its nanostructure was
investigated by pai-A isotherm and XR. All betaines formed brushes and showed carpet-only/ carpet+brush
structure transition. Quite different from simple (i.e., anionic and cationic) ionic brushes, brush thickness, in
principle, increased by salt addition.[3] This might be, so called, anti-polyelectrolyte effect. However, it was
found that brush thickness was very sensitive to salt concentration under very low salt concentration
condition; it increased and decreased and this behaviour was different for three kinds of betaine brushes.
Similar characteristic behaviour was observed also for hydrodynamic radius and zeta potential of
polybetaine homopolymers in aqueous solutions. UCST behaviour of sulfobetaine and Ion-specific effect of
added salt were also examined.

Institution

Department of Polymer Chemistry, Kyoto University, Kyoto, Kyoto, Japan.

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