Zeta-potential measurement suspension rheology

Hunter and Nicol [5] studied the flocculation and restabilisation of kaolinite suspensions using rheology and zeta-potential measurements. Figure 21.11 shows plots of the yield value (cr ) and electrophoretic mobility (i) as a function of cetyl trimethyl ammonium bromide (CTAB) concentration at pH =9. increases in line with increases in CTAB concentration, reaching a maximum at the point where the mobility reaches zero (the isoelectric point, i.e.p., of the clay), and then decreases with further increases in CTAB concentration. This trend can be explained on the basis of flocculation and restabilisation of the clay suspension. 

For the full assessment of the properties of suspension concentrates, three main types of investigations are needed (i) the fundamental investigation of the system at a molecular level (ii) investigations into the state of the suspension on standing (iii) bulk properties of the suspension. All these investigations require a number of sophisticated techniques such as zeta potential measurements, surfactant and polymer adsorption and their conformation at the solid/liquid interface, measurement of the rate of flocculation and crystal growth, and several rheological measurements. Apart... 

Suspensions are generally evaluated with respect to their particle size, electrokinetic properties (zeta potential), and rheological characteristics. A detailed discussion on the methods/techniques and relevant instrumentation is given in Sec. VII. A number of evaluating methods done specifically with suspension dosage forms, such as sedimentation volume, redispersibility, and specific gravity measurements, will be treated in this section. 

These tests were performed using a universal Zwick tester, model 1435, coimected to a computer with appropriate software. Particle size was measured in paraffin oil using Zetasizemano S90 (Malvern Instmments) analyzer. Zeta potential of filler dispersion in water was studied by the means of Zetasizer 2000 (Malvern Instruments) apparams. Rheological properties of filler suspensions in paraffin oil were determined by viscometer RM500 (Rheometric Scientific). Dibutylphtalate (DBP) absorption was measured by means of an Absorptometer C (Brabender). The modification process was carried out in Brabender Measuring Mixer N50 at following parameters temperature 125°C rotor speed 40 RPM duration 0,5 h. 

In the following, we briefly describe two examples which support our arguments for two completely different apphcations and materials. First, we discuss the influence of the zeta-potential of alumina suspensions which were studied in the context of nanomiUing in stirred media mills. The zeta-potential is a measure of the surface charge of the particles and is here used to tailor the suspension rheology. Figure 13 shows that the magnitude of the zeta-potential controls the measured shear stress at low shear rates where the influence of interparticulate interactions can be monitored. 

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