Adsorption and conformation of polyethylene imine on the SiC/water interface and effects on the dispersion stability of slurry

The adsorption of polyethylene imine (PEI) on the SiC/water interface was studied in details by adsorption isotherms and kinetics. The adsorption results indicated that PEI formed saturated monolayer coverage on the SiC surface and the adsorption reached the equilibrium within 30 min. Langmuir and pseudo-second-order models could better describe the adsorption process. The adsorption was mainly dominated by electrostatic interaction between positively charged PEI and negatively charged SiC surface. With the pH increasing from 5 to 8, the conformation of PEI on the SiC surface transformed from flat trains to loops and tails, and then the PEI adsorption capacity increased gradually so that the contact angles of modified SiC decreased from 20.9° to 13.7°, the maximum values of zeta potential increased from 37.1 to 43.9 mV and the maximum stability of modified SiC suspensions at pH 5 also enhanced. Moreover, modified SiC powder with the best dispersion was obtained with 0.5 wt% PEI at pH 6.5 and modified slurry had the low viscosity of 664 mPa·s at high solid loading of 55 vol%.