16064-83-8

The IR spectra in the 13001450 cm-1 region, which reflect the CH and CH2 deformation vibrational modes of the succinate skeleton, have been investigated in detail for sodium dialkylsulfonates (alkyl groups: Ethyl, n-propyl, n-butyl, n-hexyl, n-heptyl, n-octyl, n-decyl, and n-dodecyl) and sodium 1,2-bis(2-ethylhexyl)sulfosuccinate (sodium 1,2-bis(2- ethylhexyloxycarbonyl)ethanesulfonate) (AOT). The results have provided clear evidence that two configurations, arising from the difference in the torsion angles of the succinate skeleton, are preferentially stabilized in aqueous solution as well as in the solid state, depending upon the concentration. Thus, the IR spectra of this region can be used as a powerful tool for elucidation of the mechanism of the disorderorder transition in aggregate systems of AOT or its homologs at the molecular level.

A series of AOT (aerosol-OT) analogue surfactants (sodium salt of dibutyl-2-sulfosuccinate, sodium salt of dipentyl-2-sulfosuccinate, sodium salt of dihexyl-2-sulfosuccinate, and sodium salt of dioctyl-2-sulfosuccinate) were synthesized and characterized by 1H NMR and elemental analysis. A static method coupled with gravimetric analysis is developed to measure the solubility of the surfactants in 1,1,1,2-tetrafluoroethane (HFC-134a) and supercritical CO2 (scCO2). The solubilities of the surfactants in HFC-134a and scCO2 are affected by the temperature, pressure, and carbon atom number of the surfactant. The solubility of the same surfactant in HFC-134a solvent is approximately two times that in the most commonly used supercritical solvent CO2. The pressure-temperature phase diagrams for water/MFC-134a microemulsions stabilized by the surfactants were determined using cloud-point measurements for a concentration range of the surfactant from (1.85 × 10-3 to 5.60 × 10-3) M, temperature up to 338 K, and pressure up to 40 MPa in a high-pressure vessel. At a fixed temperature, the cloud-point pressure increased with increasing water-to-surfactant molar ratio (Wo). At a fixed Wo, the cloudpoint pressure decreased with increasing temperature. The surfactant with the longest hydrocarbon chain has the highest cloud-point pressure even at lower surfactant concentrations.

A series of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) analogue surfactants [sodium dibutyl sulfosuccinate (DBSS), sodium dipentyl sulfosuccinate (DPSS), sodium dihexyl sulfosuccinate (DHSS), and sodium dioctyl sulfosuccinate (DOSS)] were synthesized and characterized with 1H NMR and elemental analysis. The solubilities of surfactants in supercritical CO2 (scCO2) and supercritical 1,1,1,2-tetrafluoroethane (HFC-134a) fluids at a temperature range from (308 to 338) K and under pressures of (10 to 30) MPa were measured using a static method coupled with gravimetric analysis. The solubilities of these surfactants are much higher in HFC-134a fluid as compared with that in scCO2. The solubilities increased with increasing temperature and pressure for both scCO2 and HFC-134a fluids. The solubilities in scCO2 increased with increasing carbon atom number of surfactant, whereas they decreased with increasing carbon atom number of surfactant in HFC-134a. The density of scCO2 was simulated with the Peng-Robinson (P-R) equation. The experimental data were used to validate the accuracy of the P-R equation.

Headgroup-counterion interactions have been studied for a homologous series of sodium dialkyl sulfosuccinates (SDAS) with propyl, butyl, hexyl, octyl, decyl, undecyl and dodecyl chains as Aerosol-OT analogues. Raman scattering and IR absorption spectra were recorded and compared with those for dimethyl sulfosuccinate monohydrate, diethyl sulfosuccinate trihydrate and diheptyl sulfosuccinate dihydrate, whose crystal structures are known. The spectral features of the C=O and SO3- stretch modes directly reflect the interaction between the polar group and the Na+ ion and depend strongly upon the environment of hydration. The results may be summarized as follows. For the SDAS monohydrates in the solid state, there exists a strong interaction between the β C=O group and the Na+ ion, as a consequence of coordination of the β C=O to the Na+ ion, resulting in splitting of the C=O stretch modes. In particular, the common Raman (IR) bands observed at 1705- 1707 (1706-1708) and 1730-1732 (1732-1733) cm-1 may be assigned to the β C=O group coordinated to the Na+ counterion and the hydrated α C=O group, respectively. The extent of splitting of these bands is a measure of the strength of this C=O···Na+ interaction. Coordination of the β C=O to the Na+ ion also affects the C=O deformation modes of the O-C=O linkage. An increased hydration number and longer hydrocarbon chains induce a weak interaction between the C=O group and the Na+ ion. The SO3-···Na6+ interaction reflects the SO3- stretch modes, depending upon the extent of hydration. Furthermore, for the SDAS samples in the organic and aqueous microphases, Raman (IR) bands characteristic of the C=O and SO3-1 groups have been used successfully to account for the interaction between the polar group and the Na+ ion.