Structural characterization of solid trivalent metal dodecyl sulfates: from aqueous solution to lamellar superstructures

Abstract

Metal dodecyl sulfates of trivalent aluminium, chromium, lanthanum and gadolinium were prepared by addition of the corresponding salts to aqueous solutions of sodium dodecyl sulfate at the natural pH (ca. 6). Using X-ray diffraction, FT-IR and NMR spectroscopy, DSC, thermogravimetry and polarizing light thermomicroscopy it is shown that metal dodecyl sulfates are formed with lamellar structures. These have different degrees of hydration, which depend upon the metal ion. In some cases there is evidence for coexistence of different lamellar phases. The metal is strongly bound electrostatically to the sulfate group, and although the alkyl chain is in an extended conformation, there are suggestions of local disordering of the methylene groups adjacent to the anionic head group. SEM with an EDS probe on the trivalent metal complexes shows a 1 : 3 ratio at the surface identical to the bulk structure. Studies by SEM and AFM provide evidence of periodicity, which is likely to be induced by the lamellar, layered structures. Differences are observed in the thermal behavior, which appear to reflect both the coordination behavior of the metal ion and the degree of hydration.

Thermodynamic study of the interaction between 5,10,15,20-tetrakis-(N-methyl-4-pyridyl)porphyrin tetraiodine and sodium dodecyl sulfate

“…This is also suggested by the computation of the binding ratio ([SDS]/[TMePyPI 4 ]) equal to 3.1. This value although slightly lower than that expected for full charge neutralization may suggest that the structure of the aggregate also takes into consideration the hydrophobic chain of the surfactant, as suggested by previous studies on similar systems [30]. However, at binding ratios higher than the stoichiometric ones, the DS − -TMePyP +4 aggregates re-dissolve and the electrical conductivity of mix solution is somewhat similar to that observed for SDS in aqueous solution.…”

“…Besides, β values do not change with temperature. From a nominal analysis of the β values, we can conclude that the experimental β values are lower than the expected value for charge neutralization; this discrepancy may indicate that the aggregate structure is rather complex, which, on the other hand, is justified to avoid the exposition of hydrophobic chains of surfactant to water [30]. This has also been found for interaction between trivalent metal ions and long chain carboxylates [31,32] and alkylsufates [30].…”

Interactions between cationic surfactants and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin tetrasodium salt as seen by electric conductometry and spectroscopic techniques

“…Recently we have found that the use of ionic surfactants can lead to the formation of organized structures with, for example, trivalent metal ions [22]. Herein we describe the effect of N-alkyltrimethylammonium surfactants, with different alkyl chain lengths (12 and 16 methylene groups), either in unimer or micelle forms, on the equilibrium between the different possible species of meso-substituted porphyrin, in aqueous solution, using spectroscopic techniques.…”

The interaction of long chain sodium carboxylates and sodium dodecylsulfate with lead(II) ions in aqueous solutions

“…With SDS, the maximum interaction concentration is not reached at charge neutralization, but at higher r values. This leads to formation of a lamellar solid [65], which redissolves in excess surfactant due to preferential hydrophobic interactions between the alkyl chains of the surfactant, destabilizing the aggregates of dodecylsulfate (DS − )/metal ion. The fact that lead(II)…”