(382d) Functionalized Polyethylenimine for Controlling the Dispersibility of SiC Aqueous Suspentions

SiC nanoparticle is one of the promising materials expected to be applied for sintering additives, power devices and optical emission materials. However, it is difficult to improve the dipersibility of SiC nanoparticles in aqueous media because of their hydrophobic surface properties. Until today, polymeric dispersants such as polyethylenimine (PEI) has been used to disperse SiC particles in aqueous media. Controlling the adsorbed content and adsorbed structure of PEI on the particle surface is important for improvement of particle dispersion. In this study, PEI functionalized with hydrophobic toluoyl group (toluoyl-PEI) were synthesized as a novel dispersant to disperse the SiC nanoparticles in aqueous media. Since it has been reported that the hydrophobic groups of surfactant can become an adsorption segment for the hydrophobic surface, it is considered that the affinity of toluoyl-PEI for SiC surface become higher than that of as-received PEI. In order to estimate the effect of molecular weight of PEI and functionalized toluoyl group ratio of toluoyl-PEI on the dispersibility of SiC nanoparticles, toluoyl-PEI with different molecular weight and hydrophobic group ratio ranging from 0 to 40% were synthesized. The dispersability of SiC nanoparticles were evaluated by viscometer and colloid probe AFM method. When as-received PEI was added in SiC slurry at pH 4, the apparent viscosity of SiC slurry did not decrease compared with the system without dispersant. Contrary, when toluoyl-PEI with metrical molecular weight 1,800 was added, the viscosity of SiC slurry decreased. It was observed that the decrease amount of viscosity increased as the increase of the hydrophobic group ratio. From the measurement of the adsorption ratio of dispersant and the interaction between SiC nanoparticles determined by colloid probe AFM method, it was found that the adsorption ratio and the steric repulsive force between the particles increased by the functionalization of toluoyl group to PEI. When toluoyl-PEI with metrical molecular weight 10,000 which have 15 and 30% hydrophobic group ratio was added, the apparent viscosity of SiC slurry has remarkably decreased while those with 40% hydrophobic group ratio did not decreased remarkably. In the case of toluoyl-PEI with 40%, the adsorption ratio of dispersant did not change compared with that of 15 and 30%. However, the steric repulsive force between SiC nanoparticles was lower than that of 15 and 30%. From these results, it is estimated that toluoyl-PEI with metrical molecular weight 10,000 which have 40% hydrophobic group ratio thinly adsorbed on SiC surface because of their strong hydrophobicity.