Behaviour of laponite gels: Rheology, ageing, pH effect and phase state in the presence of dispersant

The zeta potential result showed that the nano-discotic laponite particles in dispersion were negatively charged across the whole pH range of 3-12. For the 3 wt% gel, no dispersed region was observed within this pH range. The yield stress decreased with increasing pH from 8 to 12. Particle agglomeration affected the yield stress result at low pH. Addition of 6 dwb% pyrophosphate peptizer increased the particle negative zeta potential and caused the 3 wt% gel to be completely dispersed at pH greater than 7. Again the yield stress increased with decreasing pH from 7 to 5. The critical volume fraction equation for the repulsive gel state or EDL caging effect to operate was found to be very useful for determining the phase state of the laponite gel by the method of exclusion. A liquid sol state was deduced for the 0.45 and 0.89 wt% laponite dispersions having conductivities equivalent to 0.0015 and 0.003 M KCl respectively. An attractive gel state was deduced for the 1.8 dwb% P2O74- shear-thinning laponite gels with concentration ranging from 1.5 to 5.5 wt% solids. The sol state was attributed to the Newtonian dispersions containing 1.1 to 1.5 wt% solids with 1.8 dwb% P2O74-. The structural recovery behaviour of 3 wt% laponite gels with 0.001 and 0.01 M KNO3, was well described by the two-parameter model of Rich et al. (2011b) and the three-parameter Leong model. The yield stress of the aged gel decreased with increasing temperature which contradicted a theoretical prediction. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.