(757f) Electrostatically Driven Adsorption of Silica Nanoparticles On Functionalized Surfaces

Self-assembly of nanoparticles (NP) on solid support is an interesting phenomenon and attracts increasing attention due to the fundamental curiosity in NP and due to their high application potential in electronic and optical devices. We exploited the electrostatic interaction between silica (SiO₂) nanoparticles and amino-functionalized substrate in order to devise a simple method for the fabrication of SiO₂ NP film.

Stöber method (a sol-gel approach) was employed to prepare uniformly sized SiO₂ NP with a diameter of 50-80 nm. Native oxide-covered silicon wafer substrates were amino-functionalized by self-assembly of a 3-aminopropyltrimethoxysilane (APS) monolayer. The adsorption of SiO₂ NP film onto the silicon wafer substrate was controlled by electrostatic interaction between the NP and the substrate. Modification of surface charge of either the SiO₂ NP or the substrate is a crucial step in the process. Thus the effect of depositon time of APS on the surface energy was investigated. Also, process parameters such as NP concentration, adsorption time and solvent composition were varied in order to investigate the NP adsorption kinetics. Moreover, NaCl was introduced to the SiO₂ suspension as a charge-screening agent to reduce the interparticle repulsion. This resulted in thicker films. Dependence of NP adsorption kinetics on salt was investigated by varying adsorption time.

Electrostatically controlled adsorption allows for uniform coverage of NP over large areas. Covalent and ionic adjustment of surface charge can be applied for depositing films of a large variety of different nanoparticles.