Surface Force Arising from Adsorbed Graphene Oxide in Kaolinite Suspensions

The mechanism of surface force, rheological and surface charge behaviours of kaolinite and graphene oxide (GO)-kaolinite suspension under various surface chemistry condition using kaolin mined in Malaysia are not clearly defined. Therefore, these properties were determined using zeta potential-pH measurements, Mular-Roberts (MR) pH-salt addition and yield stress-pH measurements at different solid concentrations. The KM40 kaolinite suspension displayed similar pH of zero zeta potential and point of zero charge (p.z.c.) at ∼5 where the maximum yield stress was located. With the presence of GO additive at 1.0dwb%, the pH of zero zeta potential was shifted to a higher pH of ∼8 similar with the maximum yield stress, with a significant increment of 63 % on the maximum yield stress. This was attributed to the arising of particle-bridging interactions between the kaolinite particles and relatively strong EDL interactions by overlapping negatively charged kaolinite particles and GO at higher pH region. However, the pH of zero zeta potential exhibited discrepancy that did not correlate well with the maximum yield stress at 0.5dwb%. The use of MR pH-salt addition method was also revealed not suitable for this case as GO was negatively charged throughout the entire pH region that did not show pH of zero zeta potential. Despite so, yield stress-DLVO relationships are still obeyed for all cases.