26 - Dispersion control of Al2O3 nanoparticles in ethanol

Abstract

This chapter focuses on the action mechanism and selection of the polymer dispersant on Al2O3 nanoparticles in ethanol suspension, based on the surface interaction using a nanocolloidal probe AFM. By using 7, 30, 100, and 370 nm scaled Al2O3 nanoparticles, the aggregation and dispersion behavior of the Al2O nanoparticles in dense ethanol suspensions is investigated, for which six kinds of branched polyethyleneimines (PEIs) with a molecular weight (MW) ranging from 300 to 70,000 are used as polymer dispersants that are effective in the dispersion of ceramic particles in ethanol. To clarify the relationship between the suspension viscosity of each nanoparticle and the MW of branched PEIs, the apparent viscosity at the same shear rate (300 l/s) of suspensions as a function of the MW of branched PEIs is also plotted. The molecular size of a polymer dispersant with approximately several nanometer affects the dispersibility of nanoparticles in dense suspensions. As the particle size of Al2O3 nanoparticles is decreased, the optimum molecular size of the PEIs to obtain a low suspension viscosity is also decreased. The optimum molecular size of PEIs for the minimum viscosity of the suspension with the 7-nm scaled Al2O3 nanoparticle is found to be about 7 nm. The microscopic surface interaction between 7-nm scaled Al2O3 nanoparticles is also investigated by using a nanocolloidal probe AFM where the repulsive force increases with an increase in the MW of the PEIs. As the particle diameter of the nanoparticles decreases, the optimum MW and molecular size of the PEIs also decrease for the ethanol suspension with good dispersibility of particle and high fluidity.