Surface Modification by the Reversible, Electrochemical Deposition of Polyelectrolyte Complex Films

Polyelectrolyte complex films made from oppositely charged polymer chains have applications as drug delivery vehicles, separation membranes, and biocompatible coatings. Conventional layer-by-layer techniques for polyelectrolyte coatings are low-throughput, multistep processes that are quite slow for building films on the order of micrometers. We have developed electrochemical processes for depositing thick ( > 1 $\mu m$ ) films within short experimental time scales ( 5 min). This rapid electrodeposition is achieved by exploiting the reduction of hydrogen peroxide at the working electrode, triggering the pH responsive self-assembly of a polyelectrolyte complex film composed of poly(acrylic) acid and poly(allylamine) HCl. In situ rheology using an electrochemical quartz crystal microbalance (EQCM) quantified the viscoelastic shear modulus of the films at a frequency of 15 MHz. The EQCM technique is ideally suited for basic studies of salt and pH-induced swelling, dissolution and deposition of PEC films. The dissolution/redeposition cycle is significant in that it provides route to ‘resettable’ fouling release surfaces.