Control of nanostructures through pH-dependent self-assembly of nanoplatelets

Abstract

HypothesisThe self-assembly of platy clay particles is influenced by anisotropic surface charging properties of the particles. The Stern potentials of particle surfaces are controlled by solution pH. Consequently, the energy-favorable particle association varies with pH, leading to different self-assembly structures. Therefore, it should be possible to form desired nanostructure of final clay product through self-assembly of clay particles by controlling the surface charge through adjusting solution pH. ExperimentsThree different surfaces of kaolinite clay nanoparticles were selectively exposed for Stern potential determination using an atomic force microscope. Aggregation structures through particle self-assembly were predicted based on the analysis of interaction energies between various types of surfaces of kaolinite particles. The structures were visually confirmed using the freeze-dried scanning electron microscopy technique. FindingsBy reducing pH of a concentrated kaolinite suspension from 8 to 5 and 3, the dispersed kaolinite particles were self-assembled to a well-stacked configuration and card-house structure, respectively. Current study demonstrates that the pH-dependent surface properties of platy kaolinite nanoparticles can be successfully used to understand the macroscopic behavior (rheology) of kaolinite nanoparticle suspensions and design nanostructures of clay products (catalysts and sorbents). The pH-dependent self-assembly is also applicable to other platy particles of anisotropic surface (charging or wettability) properties.