Electrophoretic Deposition of Hexagonal Boron Nitride Particles from Low Conductivity Suspension

Abstract

Given that hexagonal boron nitride (hBN) particles are extremely stable in colloidal suspensions due to their low density, they are difficult to deposit via electrophoretic deposition (EPD). Poly (diallyldimethylammonium chloride) (PDDA) is widely used as a polyelectrolyte for ceramic particles because of its strong electrophoretic response. Nevertheless, studies on PDDA as a functionalising agent of hBN particles for EPD remain elusive. Here, hBN particles were functionalised with different amounts of PDDA to investigate effects on suspension stability and EPD yield. Deionised (DI)-water-based hBN particle suspensions with PDDA contents that varied from 0.3 wt% and 0.6 wt% (of hBN basis) were prepared using washed as-received hBN particles. Then, washed and nonwashed PDDA-functionalised hBN particle groups were prepared by subjecting only the former to water washing. Washing, which involved the repeated particle dispersion in DI water and vacuum filtration, successfully reduced the conductivity of the aqueous hBN suspension to 2 µS/cm, which was significantly lower than the conductivities of 180 and 25 µS/cm shown by the as-received particle suspension and PDDA-functionalised particles before washing. This result indicated that washing eliminated the interference of free ions on the suspension stability of hBN particles and EPD yield. In contrast to that of the nonwashed group, the suspension stability of the washed group decreased as the PDDA content was increased. Nevertheless, at 0.3 wt% and 0.6 wt% PDDA, the EPD yields of the washed group were 183% to 31% higher than those of the nonwashed group. This study provided new insight into the EPD of hBN particles using low-cost aqueous suspensions with sustainable ultralow ion conductivity.