Layer-by-Layer Self-assembly of a Polyelectrolyte Bearing Metal Ion Coordination and Electrostatic Functionality

Abstract

A novel polyelectrolyte (BiPE) bearing permanently charged quaternary ammonium groups as well as bipyridine ligands for metal ion recognition is presented that can be incorporated into ultrathin films either through electrostatic interactions or metal ion coordination. Conventional layer-by-layer assembly of BiPE with sodium poly(styrene sulfonate) (PSS) as an oppositely charged component results in multilayers. Layer growth is linear and the resulting films are smooth and homogeneous as indicated by X-ray reflectometry, ellipsometry, and atomic force microscopy (AFM). Reflection−absorption infrared spectroscopy suggests that the counterions are exchanged during layer assembly. The BiPE/PSS multilayers can bind transition metal ions including Fe(II), Ni(II), and Zn(II). Metal ion release from the layer is induced by ethylenediaminetetraacetic acid (EDTA), a strong complexing agent. Formation of 2-D arrays of metallo-units is achieved by microcontact stamping transition metal salts onto the BiPE/PSS interface. Also, multilayers of BiPE are readily assembled through metal ion coordination. The importance of metal ion coordination for multilayer formation is demonstrated by force−distance curves measured with AFM. Due to the reversible nature of metal ion coordination, exposure of these multilayers to EDTA causes instant disassembly of the layer, a property needed to implement stimulus-triggered release functions.