Effect of sequentially adsorbed multilayers, citric acid(CA)-PEI-CA-PEI and PEI-CA-PEI-CA, on the surface chemistry and rheology of spherical α-alumina suspensions

Abstract

The yield stress and zeta potential of washed spherical α-Al₂O₃ suspensions with two to four layers of critic acid(CA) and polyethyleneimine(PEI_Mw1.8and 70 kDa) adsorbed sequentially were characterized. With CA adsorbed as the first layer, pH_ξ=0 was shifted to a lower pH and the maximum yield stress (τ_ymax) was reduced. With PEI adsorbed as the first layer, the pH_ξ=0 was moved slightly higher. With the introduction of the second layer, the CA/PEI additive was formed which functioned as a bridging agent. The pH range of yield stress was broadened significantly and increased with the number of layers. This pH ranged from 2.5 to 11. The CA/PEI multilayer additive loses its positive charge at pH >11. There was less adsorption in layer3 and layer4 when lower Mw PEI is applied to the suspension. The CA/PEI multilayer additive formed by PEI of M_w70000 and CA was larger in size than that formed by PEI of M_w 1800 and CA. Lower Mw PEI produced a stronger flocculated network or higher τ_ymax suspension due to a higher concentration of multilayer additive. CA/PEI multilayer additive was participating in bridging and particle bridging interaction was not affected by the adsorption order of CA and PEI.GRAPHICAL ABSTRACT

Keywords:

• α-alumina
• CA/PEI multi layers
• particle forces
• zeta potential