The relaxation effect as observed on lipid suspensions of low polydispersity

Lipid suspensions with a low polydispersity (delta = 0.15 +/- 0.05, as given by photon correlation spectroscopy (PCS)) were used to elucidate the origin of the disagreement between the experimental zeta potential values (zeta sm), obtained from the electrophoretic mobilities through the Smoluchowski equation, and double-layer theory prediction (zeta potential) at low salt concentrations. The values of zeta sm, measured for cardiolipin and phosphatidylserine suspensions in monovalent electrolytes, were compared with the correspondent theoretical values of the zeta potentials correlated for the relaxation effect; the correction was made according to the S.S. Dukhin theory of electrophoresis. It was found, that this correction eliminates the disagreement for cardiolipin in NaCl entirely; it partly solves the problem for cardiolipin in KCl but fails to improve the situation for phosphatidylserine in NaCl.