Meso-Structure Control of Colloidal Nanoparticles Adsorbed on a Substrate by Applying External Electric Potential

点击翻译按钮获取中文摘要

Various high-functional materials would be developed if masoscale structure of nanoparticle arrays adsorbed on a substrate can be controlled as desired. This study has been aiming at developing a methodology for controlling kinetics and structure of particle arrays by applying external electric potential to a conductive substrate onto which colloidal nanoparticles adsorb. The conclusions are as follows.1.Experimental study :Having developed an experimental system equipped with a conductive substrate with desired surface potential controlled by external electrical potential, adsorption processes of positively charged polystylene latex collodal particles were observed by ex-situ SEM observation, and by in-situ AFM observation. We found that there is a limiting surface potential of -28mV, below which colloidal particles adsorb with rather high density with almost uniform interparticle distances, and above which almost no adsorption occurs even though the potential remains negative. The re … More ason for no adsorption on the substrate with slightly negative charge may presumably be a prevention of strong adsorption by structured water layer on the surface. This kind of weakly adsorbed particles would be expected to form an ordered arrays because of extremely reduced friction on the surface.2.Theoretical study :Extensive simulations of Brownian dynamics were conducted for a electrostatically stabilized colloidal nanoparticles onto a substrate with counter charge in order to find out the nature and estimation method for "one-directional average force", which has been found to be the determinant factor for order/disorder boundary. Through comparison with the Alder transition by hard disks, we have successfully unified the criteria for order/disorder transition in both the hard-disk and colloidal systems by introducing an effective diameter for colloidal particles, which should be larger than the real diameter because of the repulsive double-layer forces. With this success a priori prediction of ordered structure and kinetics of the order-formation process can now be possible.Summarizing, a mesoscale order formation by colloidal adsorption on a surface with given potential was successfully understood and modeled analytically, which would stand for theoretical basis for the control of kinetics and structure of particle arrays on a substrate by applying external electric potential. Less