Thin Film Thickness Gradients and Spatial Patterning via Salt Etching of Polyelectrolyte Multilayers

Abstract

We demonstrate the time- and concentration-dependent dissolution (etching) of polyelectrolyte multilayer (PEM) films comprised of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) immersed in NaCl solutions. PEM thickness decreases to a reproducible unchanging value that depends upon the initial film thickness and the concentration of NaCl. As opposed to a “top-down” removal of PEM chains from the film, the dissolution mechanism involves the diffusion and association of chains throughout the PEM that leave the film in the form of polyelectrolyte complexes (PECs). The PEC phase diagram is invoked to explain the observations presented in this paper and work by previous researchers. We demonstrate the straightforward application of PEM salt etching to pattern films where the spatial position and amount of dissolved material are controlled, resulting in a multicolor reflector and a gradient-thickness film. In addition to providing a more comprehensive picture of PEM stability, these results may help to advance the technological impact of PEMs in biology and other fields where the ability to create gradients in film thickness could be advantageous.

Multilayered thin films from poly(amido amine)s and DNA

“…The presence of the charged substrate helps keep the remaining layers together, while amide hydrolysis slowly proceeds to degrade the remaining films. Similar salt-induced deconstruction has been reported previously by Ren et al and Schüler and Caruso for DNA-containing multilayers [46,47] and others [48][49][50], although mostly at higher salt concentrations than 0.15 M utilized in this study.…”

Multiple Functionalities of Polyelectrolyte Multilayer Films: New Biomedical Applications

“…It makes it possible to adjust film degradability by controlling salt concentrations. Cohen and co-workers [58] have reported this phenomenon in (PAA/PAH) films and made a proof of concept by forming a thickness gradient using this method. Such gradients could prove to be useful in the study of cell processes, as discussed in Section 5 of this review.…”

Erasable Coordination Polymer Multilayers on Gold

“…Upon exposure of a multilayer to a 10 mm solution of PPh 3 , a stronger base and a tighter coordinating ligand for the Pd II complexes along PNBE + , the absorbance intensity decreased dramatically within a few minutes (Figure 1 B), thus demonstrating the removal of our multilayers and suggesting another possible trigger mechanism for top-down patterning. [22] In summary, we have demonstrated that coordination chemistry between polymer-supported palladium complexes and polymeric bases can be used to assemble CoPMs. The CoPMs produced in this fashion rival the stability of covalent multilayers in the solid state and most organic solvents, while retaining the responsiveness of PEMs, thus adding a new surface functionalization method with unique properties to surface scientists "toolbox".…”