Collaborative studies of zeta-potential measurements and electrophoretic measurements using reference sample

Simultaneous measurements of zeta-potential for two standard latex suspensions were carried out so as to assess the reliability of each of these measurement techniques and find means for their improvement. Furthermore, syntheses of a reference particle dispersion stabilized sterically in an aqueous medium without any electrostatic effects and measurements of zeta-potential using the reference dispersion as a standard were performed under various experimental conditions. It became apparent that the dense adsorption layer of hydroxypropylcellulose (HPC), with a lower critical solution temperature (LCST), formed on latex particles with a low surface charge density at temperatures higher than the LCST, plays a role in completely shielding the electrostatic effect arising from the surface charge on the bare particles. Such reference particles with zero zeta-potential allow us to determine the electrophoretic mobility of unknown samples at the one-half depth in the electrophoretic cell by subtracting the mobility of the reference sample at the same level. Furthermore, the zeta-potential of the cell wall can be easily determined from the mobility of the reference sample, because the apparent velocity profile of the reference sample indicates the liquid flow velocity in the cell.