Investigation on the conformations of AOT in water-in-oil microemulsions using 2D-ATR-FTIR correlation spectroscopy

The carbonyl groups of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in the water-in-oil (W/O) microemulsions of AOT/tetrachloromethane/water were investigated by using two-dimensional attenuated total reflection Fourier transform infrared (2D-ATR-FTIR) correlation spectroscopy under a perturbation of temperature. The results of a traditional curve fitting method were compared with the 2D correlation spectra results. The peaks at 1718 and 1736 cm(-1) were assigned to different carbonyl groups in trans conformation and gauche conformation of AOT molecules, respectively. With the increase of temperature, the trans conformation increased quickly at the lower temperature below 35 degrees C and decreased slowly at the higher temperature. The special phenomenon owed to the composition and decomposition of the hydrogen bonding between water of the inner polar core and carbonyl groups of AOT molecules. Two new peaks at 1707 and 1747 cm(-1) in the 2D correlation spectra implied the process of the transition of AOT molecule conformation and the deviation of correlation coefficients of curve fitting method. 2D-ATR-FTIR correlation spectroscopy exhibited the superiority over the traditional curve fitting method. (C) 2008 Elsevier B.V. All rights reserved.