Noboru Moriyama

Mixed micelle formation of anionic and nonionic surfactants

Abstract The effects of a series of nonionic surfactants, dodecyl polyoxyethylene ethers (DPE), on the micellization of an anionic surfactant, sodium dodecyl sulfate (NaDS), have been studied as a function of the mole ratio of NaDS DPE and of the polyoxyethylene chain length of the DPE molecule. Attention has been paid to changes in the degree of ionic dissociation of NaDS brought about by its incorporation in mixed micelles. The degree of ionic dissociation of the mixed micellar species was evaluated both from osmotic and pNa data. It has been shown that the degree of ionic dissociation of the ionic surface-active material in the mixed micelle increases as the proportion of the nonionic material increases and as the polyoxyethylene chain of the nonionic material is lengthened. The specific conductivities of the mixed solutions of NaDS and DPE at low concentrations are smaller than those of the solutions of NaDS alone, whereas at high concentrations the former are greater than the latter; the results would be explained by the degree of ionic dissociation and the mobility of the mixed micelles.

Stability of aqueous ferric oxide suspension

Abstract The effects of various types of surfactants and inorganic phosphates on the stability of aqueous ferric oxide suspensions have been examined. The stability was evaluated from sedimentation velocity data. At low concentrations the stability increases with concentrations of surfactants and inorganic phosphates, whereas at high concentrations it decreases remarkably with increase in concentration above a certain value, which depends upon chemical compositions and molecular weights of surfactants or inorganic phosphates. Both the absolute values of zeta potentials and the amounts of adsorption increase with increases in the concentrations. There exists a correlation between stability data and zeta potential data or adsorption data at low concentrations. Correlations between stability data and zeta potential data or adsorption data, on the other hand, do not exist at high concentrations. Marked decreases of the stability at high concentrations may be due to the depression of electrical repulsion owing to the compression of the thickness of the double layer. The stability data in the systems of 1-1 type surfactants such as sodium dodecyl-benzene sulfonate and sodium dodecyl sulfate can be explained by applying the D.L.V.O. theory qualitatively. The stabilities undergo the effects of pH, particularly in the systems of inorganic phosphates, when pH values of the systems are changed.

The stability of aqueous ferric oxide suspensions and its relation to the chemical composition of anionic surfactants

Abstract The effects of alkyl chain length and chemical composition of 1-1 type anionic surfactants on the stabilities of aqueous ferric oxide suspensions are examined. The stabilities were evaluated from sedimentation velocity data. The stabilities increase remarkably with the concentration of surfactants at low concentration, whereas they decrease remarkably at high concentration. The concentration ranges in which the stabilities of the suspensions increase remarkably are shifted to the low concentration with increases in alkyl chain lengths of surfactants. The degrees of the stabilities at the concentrations showing the most stable suspensions are different with different alkyl chain lengths and chemical compositions, particularly, the positions of the benzene ring of the surfactants. Similarly, the concentration ranges in which the stabilities decrease remarkably at high concentration are different with different alkyl chain lengths and chemical composition of surfactants. The stability data are closely related to the concentration of surfactants and zeta-potential data in the systems.

The pNa Study of Mixed Solutions of Surfactants and Polymers

The concentration of the free counterion of an ionic surfactant has been measured for the mixed polymer-surfactant solutions, and the degree of ionic dissociation (α) of the surfactant has been calculated from the pNa data of these mixed solutions. The polymers examined were polyvinylpyrrolidone (PVP), polyethylene glycol (PEG) and polyvinylalcohol (PVA), and the surfactant was sodium dodecyl sulfate (NaDS). The value of α increases with increase in mixing ratio of polymer/NaDS (monomer unit mol/mol) and tends to decrease with increase in the molecular weight of polymer. The absolute value of α increases in the order PVP>PEG>PVA, namely in the order of increasing hydrophobic character of the polymer. From these results, authors discussed the mode of binding of NaDS onto these polymers. It was suggested that the surfactant is bound onto PVP or PEG forming aggregates on it in such a manner as micelle formation, but onto PVA the surfactant is bound monomolecularly.