(742g) Experimental Examination of Irreversibility of Electrostatically Driven Adsorption of Silica Nanoparticles At Solid-Liquid Interface

Adsorption of colloidal nanoparticles (NPs) at solid-liquid interface is a scientifically interesting and technologically important phenomenon due to the fundamental importance in many industrial, environmental, and biological processes, such as wastewater treatment, chromatography, papermaking, or biocompatibility. The process is well understood theoretically by the random sequential adsorption (RSA) model, based on the assumption of irreversible adsorption. Irreversible adsorption is defined as a process in which, once adsorbed, a particle can neither desorb, nor to move laterally on the surface. A great number of reports have confirmed the accuracy of the RSA model. However, experiment data in literatures to verify the irreversibility of particle adsorption is very limited. In this study, we demonstrated the irreversibility of electrostatically driven nanoparticle adsorption utilizing a carefully selected set of experiments.

      SiO₂ NPs with a diameter of 50-80 nm prepared by Stöber method (a sol-gel approach) was firstly electrostatically adsorbed onto amino-functionalized silicon wafer substrates. Then the substrates were rinsed but no drying procedure in order to get rid of the aging effect. Subsequently, Ag@SiO₂ core/shell NPs of the same size as well as surface chemistry with SiO₂ NPs were performed the second adsorption as exchange agent. Adsorption time for the second step was varied from 1min to one week. Surface coverage quantification has shown that the surface coverage of the first adsorbed SiO₂ NPs stays the same no matter how long the subsequent adsorption of Ag@SiO₂ core/shell NPs was performed. Furthermore, the surface coverage for one kind of NPs adsorption is equal to the total surface coverage for two kinds of NPs adsorption when the treated time is the same. All the results confirmed the irreversibility of electrostatic adsorption of NPs.