Cation–surfactant interactions in aqueous alkylphenoxypolyoxyethylene salt solutions. A Raman spectroscopic study

Abstract

Raman difference spectroscopy has been employed to elucidate the effect of the alkali-metal (Li', Na+, K + , Rb+ and Cs') and alkaline-earth-metal cations (Mg2+, Ca2+, Sr2+ and Ba") on the polyether chain conformations of alkylphenoxypolyoxyethylene-type surfactants, C,H, ,Ph(CH,CH,O),OHwhere n" = 9.5, in aqueous media. A band appeared at ca. 868 cm-' in the spectrum of the surfactant upon the addition of some cations: this feature is assigned to a surfactant-cation complex incorporating a polyether chain exhibiting a TTGTTG (T, trans; G ; gauche ; G, gauche minus) or similar conformation sequence. The surfactant complexed preferentially to Ba2+ and K + , with :he effect being greater for the former ion. A Ba2+ concentration-dependence study suggested that 1 : 2 and 1 1 3 surfactant-cation complexes are formed in the surfactant-water-salt system. The 1 : 3 coordinate complex appeared to be dominant. Models are proposed for the structure of these complexes.

Highly ordered periodic mesoporous ethanesilica synthesized under neutral conditions

“…When the inorganic salts MX n (such as NiCl 2 ) are added during the synthesis, the metal cation M n+ can be coordinated with the PEO chains to create a crown-ether-like complex. 37 This complexation will make the hydrophilic head group of the surfactant more rigid and confer a global positive charge to it. 38 The formed complex can interact with the partially negatively charged organosilica oligomer and the counter ion X 2 through electrostatic forces.…”

The effect of dilute electrolytes on the formation of non-ionically templated [Si]-MSU-X mesoporous silica molecular sieves

“…This creates helical crown ether-like metal±PEO complexes. 30 In the silicate templating environment, this complexation (prior to silicate addition) seemed to cause the H-bonding sites (i.e. EO groups) to become unavailable for templating or silicate hydrolysis.…”

“…In this way, it can be conceived that the cation modi®ed template molecules will not be homogeneously distributed. According to Siew et al 30 a PEO surfactant will coordinate 3±4 alkali or alkali-earth cations for every 10 EO groups. Therefore, 5 mol% cation loading with respect to silica produces 0.4 M z per R-(EO) 10 surfactant molecule.…”

Perfluorocarboxylic acid counter ion enhanced extraction of aqueous alkali metal ions with supercritical carbon dioxide

“…Unfortunately, alkali metal ions, such as sodium or potassium, do not readily form complexes because they have no orbitals to form coordinate bonding with typical ligands, and to date the only known examples for the alkali metal are complexes formed with ligands such as crown ethers and other macrocyclic compounds such as valinomycin, or non-macrocyclic compounds such as surfactants that have polyoxyethylene (POE) chains. [8][9][10] The interaction between alkali metal ions and these compounds are mainly electrostatic, whereas the alkali metal complexes formed with these ligands are known to be polarized ion pairs, hence their solubility in non-polar solvents such as hexane is very low. Similarly, their solubility in scCO 2 is also expected to be low.…”