Electrochemical Devices Via Electrostatic Nanoscale Assemblies
Paula T. Hammond, Chemical Engineering, Massachusetts Institute of Technology, 77 Massachuhsetts Avenue, 66-550, Cambridge, MA 02139
The alternating adsorption of oppositely charged molecular species, known as the electrostatic layer-by-layer (LBL) process, is a simple and elegant method of constructing highly tailored ultrathin polymer and organic-inorganic composite thin films. We have utilized this method to develop a number of functional ultrathin film systems, including materials that can be tailored for display, sensor and protective coating applications. These systems have allowed the formation of a range of electrochemical devices using multilayer assembly, including the use of conjugated polymers and inorganic nanoparticles for electrochromic displays, the formation of thin films as proton exchange membranes in fuel cells, and the use of these multilayers in other power and micropower devices. New explorations have also included the use of some of these unique redox active organic/inorganic hybrid systems as systematically deconstructible thin films with potential uses as an electrochemical means of drug delivery. All of these systems rely on the ability to control the placement of different multiply charged components within specific regions of the film. Some of the polyion systems of interest in these applications undergo some degree of interdiffusion during the assembly process. The nature of this interdiffusion, and means of controlling the interdiffusion process are discussed, as well as the final device applications of these systems. Means of using the interdiffusion phenomenon in an advantageous manner to create ordered virus-polymer thin film assemblies will be discussed, and collaborations at MIT in which these viruses are genetically engineered to support the generation of metal and metal oxide coatings will be described. In these systems the use of electrostatic assembly methods leads to the spontaneous assembly and ordering of viruses at the top surfaces of functional polyelectrolyte multilayers. The protein coats of the viruses act as templates to form Au, Co and CoO nanowires that can be used to make a number of interesting electrochemical functions, including battery electrodes with extraordinarily high capacity.