Humidity-tunable electronic conductivity of polyelectrolyte multilayers containing gold nanoparticles

Ostendorf A, Cramer C, Decher G, Schönhoff M

Abstract

The frequency-dependent conductivity of polyelectrolyte multilayers (PEM) containing gold nanoparticles was investigated as a function of relative humidity (RH). Multilayers were prepared from poly(allylamine hydrochloride) (PAH) and gold nanoparticles (Au-NP). Impedance spectroscopy revealed that the dc conductivity of PEM-containing layers of Au-NP is ~5 orders of magnitude higher than the dc conductivity in PEM made solely of polymeric constitutents. An electronic conductivity is inferred, where electrons are transported via tunneling between adjacent gold nanoparticles. Humidity-dependent measurements show that the dc conductivity decreases with increasing relative humidity, and reversibly increases again when RH is decreased. This is attributed to swelling of the polyelectrolyte chains between adjacent particles, leading to larger distances and lower tunneling probabilities. The conductivity of PEM doped with Au-NP can be reversibly tuned over many cycles by varying the relative humidity. In addition, the salt content of the polyelectrolyte solutions has a major influence on the film conductivity, which is attributed to different conformations of adsorbing chains controlling the interparticle distances. The electronic transport is considered to be a tunneling process with a sensitive dependence on film parameters, thus presenting the possibility of preparing films with tunable electronic conductivity. We show that conductivity can be controlled either during preparation by the choice of deposition conditions or after preparation by tuning through humidity-induced swelling/deswelling of the films.