(93c) Electrostatically Driven Particle Adsorption On Polyelectrolyte or Chemically Functionalized Substrates

Layer-by-layer electrostatic assembly using polyelectrolytes is a versatile approach for obtaining nanoparticle (NP) multilayers. The outcome is dependent on pH and ionic strength that affects both the magnitude of charge on the polyelectrolyte chain and the NP surface, as well as conformation of the polyelectrolyte chains. Motivated by improved packing of NPs and better understanding of the electrostatic adsorption process, we have characterized the adsorption of different nanoparticles (e.g. silver, silica, manganese dioxide) on functionalized surfaces. We utilized poly (diallyldimethylammonium chloride) (PDDA) as the polyelectrolyte that binds both to the substrate and the adsorbate particles electrostatically (physisorption), and comparatively also (3-aminopropyl) trimethoxysilane (APS) that will bind on oxide-covered substrates (e.g. silicon wafers) by covalent chemical bonds. APS possess an ionizable amino group that will attract oppositely charged NPs. The two systems (PDDA and APS) provide useful insight into (ir) reversibility of the NP adsorption. NP desorption has to be separated from the desorption of the PDDA or APS molecules themselves. Our choice of different NP in turn allows accounting for the effect of particle physico-chemical properties and particle size and morphology on the NP packing in the film.

To gain insight into the actual mechanism of the adsorption process, efforts are made to ascertain the rate determining transport step and hence propose a model describing the kinetics of the electrostatically driven adsorption process. The experimental saturation NP packing density and the kinetics of the adsorption on the substrate were compared with Random Sequential Adsorption model. Parameters influencing the process are thought to be the ionic strength of the suspension fluid, pH of the suspension that would govern the charge density on both the interfaces, particle size, temperature of adsorption and the bulk concentration of the particles. To account for these parameters kinetic runs were carried out with different substrates and particles as described above and we investigate if the Random Sequential Model can satisfactorily describe the adsorption process in cognizance with the experimental results taking into account the parameters mentioned above. 

We seek to apply our expertise of NP electrostatic assembly to nanostructured battery cathode fabrication of MnO₂ and nickel particles for the Zn/MnO₂ battery.