The Raman Spectra and Molecular Conformations of Surfactants in Aqueous Solution and Crystalline States

Abstract

The Raman spectra were measured for sodium alkyl sulfates and potassium aliphatic carboxylates in the solid state and aqueous solutions. Vibrational assignments of Raman lines were made, and characteristic Raman lines of the alkyl sulfate ion were identified. The ethyl sulfate ion in the aqueous solution was found to exist predominantly as the trans form about the CH2–O bond. For higher alkyl sulfate ions in aqueous solutions, Raman lines due to rotational isomers with gauche CH2–CH2 bonds were observed. Longitudinal accordion frequencies of the solid state and aqueous solutions were compared in order to discuss the conformations of hydrocarbon chains in solution.

The Raman Spectra and Conformational Change of Simple Sodium Alkylsulfates and Sodium Alkyisulfonates in Aqueous Solution

“…The Raman spectra of aqueous and solid SES were found to be much the same; no new Raman lines appeared when the solid was dissolved in water. This observation indicates that the ethylsulfate ion in an aqueous solution exists primarily in the trans form [12], In the present study, Raman spectral measurements of SES were made at various concentrations. No Raman lines due to the gauche form of ethylsulfate ion were observed in the concentration range of 0.67-5.41 mol/1.…”

“…The peak height of the 839 cm -1 line of the all trans form relative to that of the 878 cm -1 line of the gauche isomers [12]. / 839 // g78 , was found to be 1.0 at 0.87 mol/1 and 1.4 at 3.13 mol/1.…”

“…sodium n-propylsulfate (SPS), sodium * Application Laboratory, JASCO Co. Ltd., Hachioji. phatic carboxylates (n s 6), linear relations between the reciprocal number (1/«) of C atoms and the accordion frequency in the solid state have been reported by Okabayashi et al [12]. Recently, for monoalkyl and dialkyl phosphate ions such a linear relation was also found [13], The accordion frequencies may be observed even in aqueous and liquid crystalline forms, and are useful for studying molecular conformations in aqueous solutions.…”

“…can be used as a measure of the conformational change of the hydrocarbon chain [3][4][5], For SBS and SHS in aqueous solution, no Raman line corresponding to gauche isomers (1080 cm -1 ) is observed, owing to the very strong 1063 cm -1 line assigned to the SOj symmetric stretching vibration [12], The 1022 cm -1 line of SBS and the 987 cm -1 line of SHS are assigned to the gauche isomers of the alkyl chains. The J mi!…”

A Carbon-13 Spin-Lattice Relaxation Studies of Simple Alkylsulfates and Alkylsulfonates in Aqueous Solution

“…For monomeric SPS, SBS, SHS and SOS solutions, a preferential stabilization of the conformation about the CH?-0 bond possibly occurs [6], This causes a restriction of the CH 2 -0 segment, which results in the shortest T\ of the C-l atom nearest to the sulfate group.…”