Electroacoustics: zeta potential measurement in concentrated dispersions

The zeta potential is defined as the electrical potential difference at the shear plane of a moving particle in a liquid medium. Thus, it is a characteristic parameter for the electro-chemical properties of an emulsion droplet or rigid particle in a liquid: it gives some indication of the dispersion stability and the particle mobility in external electric fields. The isoelectric point (IEP), the zero point of the zeta potential is an important value: the particles agglomerate and the dispersion tends to flocculate.

Instruments

DT-300: Determination of zeta potential DT-310: Determination of zeta potential incl. titration unit	DT-1202: Particle size measurement 5 nm – 1000 µm; measuring in original concentration up to 50 Vol.-%; determination of zeta potential

Measurement principle

The electroacoustic method is using the measured colloidal vibration current (CVI) to calculate the zeta potential of a dispersion. The figure is showing the DT-310 with its the zeta potential probe (including titration unit, temperature-, pH- and electrical conductivity probe).

Using this method, an ultrasound pulse is directly coupled into the suspension or emulsion, which has to be analysed. Regarding the continuous phase, the colloid particles are displaced to a relative motion due to their inertia, whereby they are moved relatively to the diffuse double layer. This effect creates fluctuating dipole and an electric alternating current (CVI) is generated, which can be measured as a potential between two electrodes. The zeta potential is finally calculated from that parameter
The main advantage of the electroacoustic is the possibility to analyze the zeta potential of measure in high as well as low concentrated dispersions (0,1 – 50 vol.-%). Thus a dilution, which normally leads to a modification of the zeta potential, is not necessary. The instruments of the DT-line can be equipped with several useful options like electrical conductivity probes for aqueous and organic dispersions, special designed measurement setups for concentrated slurries and cements and more.
The following figure is showing exemplarily the zeta potential vs. pH dependence of two 40 wt.-% concentrated ceramic suspensions. Both were measured using a DT-310, the titration experiment was done fully automatic. Both slurries show a different dependence on the pH. From the graph the pH-area, were the dispersions are stable can be read as well as the location of the isoelectric point (IEP).

Zeta potential-vs.-pH-value of two high-built two-component suspensions

References and norms

/1/ ISO 13099-3 Colloidal systems – Methods for zeta potential determination.
/2/ A. Dukhin, P. Goetz: Characterization of Liquids, Nano- and Microparticulates, and Porous Bodies using Ultrasound. 2nd Edition. Oxford: Elsevier, 2010.
/3/ PARTICLE WORLD 19; p. 18 – 19; „Characterization of liquids, dispersions, emulsions and porous materials using ultrasound“