ABSTRACT
Zeta-potential measurements can provide valuable information necessary for preparing stable colloidal suspensions in many applications, including food preparation, agriculture, pharmaceuticals, the paper industry, ceramics paints, coatings, photographic emulsions, etc. The concept of zeta potential is also very important in such diverse processes as environmental transport of nutrients, sol-gel synthesis, mineral recovery, wastewater treatment, corrosion, and many more. The historical prominence of zeta potential, ζ, in colloid and surface science has been due to its experimental accessibility via measurement of the electrophoretic mobility, μ which is the terminal velocity of the particle, v, per unit field strengtht, E :
(1) In an externally applied electric field, ζ can be calculated from the mobility using the
simple Smoluchowski relationship [1]:
where ε and η are the dielectric constant and viscosity of the medium, respectively. At present, a continuing problem with the measurement of the electrophoretic mobility, particularly where quantitative information is required, is the lack of universally recog nized standards for interlaboratory comparison and calibration of the various commercial instruments. This problem is compounded by the observed variability between measure ments on similar materials obtained from different laboratories or users [2, 3]. There are many possible instrumental origins of this variability, including improper alignment of measurement optics, incorrect determination of the cell position, dirty cell walls, and deteriorated electrodes. Variations may also occur due to sample-related problems such as contamination, chemical and dispersion instability, errors in pH measurement, etc. The research community has long recognized the need for mobility standards to address these and related problems [4, 5].
