Monica I. El Seoud

Alkylammonium dialkylarsiante surfactants in organic solvents: Aggregation and water solubilization studies

Abstract The aggregation of butyl-, octyl-, and dodecylammonium di-2-ethylhexylarsinate in C 6 D 6 , CDCl 3 , and CCl 4 was studied by PMR spectroscopy. The variation of the chemical shifts of the magnetically discrete protons as a function of the stoichiometric concentration of the surfactants indicates that the − N + H 3 and −AsO 2 − ions are located at the aggregate interior. A multiple equilibrium aggregation model was applied to the PMR data, the equilibrium constant for aggregation, and the aggregates distribution calculated. Both quantities depend on the chain length of the alkylammonium moiety, and on the solvent polarity. Compared to the corresponding alkylammonium diethylarsinates the title surfactants show higher aggregation tendency, probably due to the diminished solvent-head-ions interactions. The polarity (Z value) of the water solubilized by dodecylammonium dietyl-, and di-2-ethylhexylarsinates in chloroform showed marked dependence on the [water]/[surfactant] ratio. Higher Z values were obtained in the case of the latter surfactant, reflecting weaker interactions of the head-ions with the solubilized water. The obtained Z values indicate micellar cores whose polarities lie between those of dichloromethane, and acetonitrile or t -butanol.

On the determination of the critical micelle concentrations of alkylammonium propionate surfactants using 7,7,8,8-tetracyanoquinodimethane (TCNQ)

Abstract The critical micelle concentrations (CMCs) of alkylammonium propionate surfactants determined by TCNQ solubilization are lower than those determined by PMR spectroscopy. The differences are due to the occurrence of a chemical reaction between the dye and the surfactants. This reaction proceeds similarly to that between the parent amines and TCNQ. First, the TCNQ anion radicaI (TCNQ − ) is produced, followed by substitution of one or two of the cyano groups. The ratio of the reaction products depends on the initial surfactant: TCNQ ratio.

Interactions of alkylammonium propionate surfactants with 7,7,8,8-tetracyanoquinodimethane

Alkylammonium propionates react with 7,7,8,8-tetracyanoquinodimethane (TCNQ) in organic solvents to produce the TCNQ anion radical and monoamino-tricyanoquinodimethane in a ratio that depends on the initial surfactant-TCNQ ratio; this may affect critical micelle concentration determinations using TCNQ.