Micelle Formation Effect on Electroacoustics in an Aqueous Surfactant Solution: Colloid Vibration Current and Ion Vibration Current

Abstract

We measured the ultrasonic vibration current of aqueous solution of dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) as a function of surfactant concentration at 298.15 K under atmospheric pressure. The dependence of vibration current on the surfactant concentration exhibited a break point around the critical micelle concentration (CMC) in the DTAB system, whereas no break point was observed in the DTAC system. Taking account of the theory for vibration current, this suggests that the vibration current in the concentration regime higher than CMC depends on the electrostatic properties of micelle surface. From the difference in the slope of vibration current versus molarity curve above CMC, it was found that the z-potential of DTAC micelle is larger than that of DTAB micelle. This can be explained by the dissociation degree of counterions from the micelle surface. In addition, the theoretical equation of vibration current enabled us to estimate the partial molar volume of surfactant ions from the different behavior of vibration current in the concentration regime lower than CMC.

Effect of Ionic Surfactants on Ion Vibration Current and Colloid Vibration Current

“…Cationic surfactants, decyltrimethylammonium bromide DeTAB 9 , dodecyltrimethyl ammonium bromide DTAB 6 , and tetradecyltrimethylammonium bromide TTAB 10 purchased from Wako Pure Chemical Industries, Ltd., and anionic surfactants, lithium dodecyl sulfate LiDS, Sigma-Aldrich Co. 11 and lithium perfl uorooctane sulfonate LiFOS, Wako Pure Chemical Industries, Ltd. 11 were purified appropriately by recrystallization from the mixture of organic solvents. The purity of surfactants was checked by observing no minimum on the surface tension versus molarity of aqueous solution of surfactants curves around the cmc.…”

“…In our preliminary work 6 , it was found that a break point appears at the concentration around the cmc on the ultrasonic vibration current versus surfactant concentration curve, and therefore, the micelle formation affects the ultrasonic vibration current in the aqueous solution of ionic surfactants. In addition, we clearly observed the effect of counterion on CVI as well as IVI by comparing the results of dodecyltrimethylammonium bromide DTAB and dodecyltrimethylammonium chloride DTAC system.…”

“…The probe of this instrument can generate an acoustic pulse by a built-in piezoelectric device, and at the same time, detect the variation of an electric field in the aqueous solution at its surface. The details of this apparatus have been explained elsewhere 6,12 . The frequency of irradiated ultrasonic wave was fi xed at 3 MHz in this study.…”

Study on Colloid Vibration Current in Aqueous Solution of Binary Surfactant Mixtures: Effects of Counterions and Hydrophobic Chains

“…The details of this spectrometer have been described elsewhere 2 . The frequency of ultrasonic waves generated from a piezoelectric device in the probe was held at 3 MHz in this study, and the probe was calibrated by measuring the ζ -potential of standard colloidal silica Ludox TM-50, Nihon Rufuto Co., Ltd. , which yields 38mV.…”

“…2 The CVI values were affected by the type of counterion due to the difference in ζ-potential between different micelle particles. 3 The alkyl Abstract: In order to elucidate an electroacoustic phenomenon of mixed micelles in an aqueous solution, we measured the colloid vibration current (CVI) in aqueous solutions of binary surfactant mixtures.…”