The relaxation effect as observed on lipid suspensions of low polydispersity

Abstract Lipid suspensions with a low polydispersity ( Δ = 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 ( ζ sm ), obtained from the electrophoretic mobilities through the Smoluchowski equation, and double-layer theory prediction (ζ potential) at low salt concentrations. The values of ζ sm , measured for cardiolipin and phosphatidylserine suspensions in monovalent electrolytes, were compared with the correspondent theoretical values of the ζ potentials corrected 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.