A new instrument for the measurement of very small electrophoretic mobilities using phase analysis light scattering (PALS)

A new instrument based on the principles of phase analysis light scattering (PALS) applied to the measurement of electrophoretic mobilities has been produced. Such measurements are particularly useful in the study of dispersions in non-polar media since for a given zeta potential, the mobility is proportional to the dielectric constant. It is also potentially useful where mobilities are low and the use of high electric fields (a traditional remedy) is inappropriate. This is the case when the ionic concentration and hence conductivity of the medium is high. The PALS configuration has been shown to be able to measure mobilities at least two orders of magnitudes lower than conventional LDE. The device is based on developments reported elsewhere (J. Miller et al., J. Colloid Interface Sci. 143 (2) (1991) 1]), but has a number of new features. In particular, all the signal processing is digital and the optical system a reference beam configuration.