The surface properties of phospholipid liposome systems and their characterisation

An equation is derived to evaluate the potential energy of interaction between the electrical double layers on two dissimilar spherical particles, one of which is characterized by a constant surface potential and the other by a constant surface charge density. The analysis is based on the Debye—Huckel approximation and the Derjaguin integration method. The results are compared with those for the situations where (a) both particles maintain a constant surface potential and (b) both particles maintain a constant surface charge density during double layer interaction. Some circumstances in which the mixed case is important are discussed. An evaluation of the validity of the Debye—Huckel approximation for spherical double layers is included.

The potential energy of interaction between dissimilar electrical double layers

Interfacial Electrochemistry of Silver Iodide

The prevailing concept that positive-edge to negative-face attraction accounts for the rheological behavior of montmorillonite suspensions at low electrolyte concentration was investigated. In one experiment, Mg2+ released from Na-montmorillonite was measured at several NaCl concentrations; in a second experiment, the viscosity, η, and the extrapolated shear stress, θ, were measured at several clay concentrations, pHs, and NaCl concentrations; and in a third experiment, the absorbance, A, was measured at two wavelengths (450 and 760 nm) at different clay and electrolyte concentrations. The released Mg2+ decreased with increasing NaCl concentration until it became zero at a NaCl concentration between 0.01 and 0.02 M, depending on pH. Thereafter, it increased with increasing NaCl concentration. Both θ and η were highly correlated with the amount of released Mg2+. Also, A remained constant until the NaCl concentration corresponded to that at the minimum of θ. Thereafter, it increased and became linearly related to θ. These results suggest: (1) positive-edge to negative-face interaction cannot solely account for the rheological properties of montmorillonite at low electrolyte concentration, and (2) the release of octahedral Mg2+ from montmorillonite affects θ, because it reduces the negative charge on the particles and, thereby, the repulsive force between them

R. H. Ottewill

Papers

The stability of hydrophobic sols in the presence of surface-active agents. Part 1.—Theoretical treatment