Phase behavior and dielectric spectroscopy of the sodium dodecyl trioxyethylene sulfate/n‐butanol/water system

Abstract

The phase diagram of the ternary system of sodium dodecyl trioxyethylene sulfate ( SDES )/n-butanoVwater is obtained at IntroductionIt is well known that surfactants in an aqueous solution could form micelles at a concentration higher than the critical micelle concentration (cmc) . Knowledge of alcohol solubilization in aqueous micelle solutions is important in understanding the aggregation behavior of such systems and is relevant to several industrial processes.' Many studies have been reported on phase behavior of ternary systems of ionic surfactant, alcohol, and water. '-' Generally, in the case of short chain alcohol, a transparent, isotropic, and low-viscosity phase appears extending from the water corner to the alcohol comer, which is called L phase. This region divides into two subregions, L1 and Lz, namely normal micelles and reverse micelles . Conductivity measurements can determine different microstructures in L phase of an ionic surfactant system. Dielectric Relaxation Spectroscopy (DRS) is a noninvasive and rapid method for the structural characterization and quality control of materials, because it only needs a small a. c . voltage and it is very sensitive to molecular motion and structure.' DRS is an effective tool to probe the physicochemical properties and inner structure of a system. It has been successfully used to determine the structural, dynamic, and electric properties of some molecular organized assembles. 9*10 Many reports have been focused on dielectric relaxation behavior of such systems in high frequency range 106-10'1Hz. 'I-'' A few researchers have primarily investigated that in low frequency range. 16*17In this paper, the ternary phase diagram of sodium dodecyl trioxyethylene sulfate ( SDES ) / n -butanol/water is obtained and phase behavior is discussed. DRS in low frequency range from 5 to I d Hz is applied to examine structure transition when one component content of the system varies, and it is in good agreement with the results obtained from phase diagram and conductivity measurements. Experimental MaterialsAnionic surfactant, sodium dodecyl trioxyethylene sulfate ( SDES 1, with the formula C H~( C H~)~I -( O C H Z C H Z )~O S O~N~, purchased from Henkel Ltd. (Germany), was recrystallized three times from ethanol and characterized by the melting point ( 148-150 T) and cmc ( 2 . 5 x 10-moVL , no minimum point ) . n -Butanol was of analytical reagent grade. All samples were prepared with deionized water. Samples for phase diagram were prepared by weighing the desired amount of SDES and n-C4H90H with a varying weight ratio from 0 : 10 to 10 : 0. Deionized water was added to the samples gradually while stirring at (30.0 * 0 . 1 ) "c . The isotropic uniphasic region ( L phase) of the phase behavior was determined by visual observation and conductivity measurements, and the liquid crystalline region was not studied in this paper. Conductivity measurementsConductivity measurements were performed with a conductometer ( Model DDS-1 1A , Shanghai Instrument Ltd., China) and a glass elec...