WALLIS utilizes Laser Doppler Electrophoresis (LDE) to determine the zeta potential of particles in liquids.
An alternating electrical field/voltage is applied between two electrodes
immersed deeply in the colloidal suspension; because of electrostatic forces,
the charged particles located in between the electrodes undergo a translational
motion (electrophoresis). The speed (v ) is directly proportional to the applied
electrical field by a factor μe called the electrophoretic mobility.
This parameter μe is determined in a very accurate manner by measuring the
corresponding Doppler frequency shift fDoppler using a high sensitivity optical
heterodyne interferometer scheme.