Micelle formation effect on electroacoustics in an aqueous surfactant solution: colloid vibration current and ion vibration current.
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 zeta-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.
Faculty of Pharmaceutical Sciences, Tokyo University of Science, Noda, Chiba, Japan. yoichit@rs.noda.tus.ac.jp
Youichi
Y
Takata
Tatsunari
T
Miyayama
Toshiaki
T
Nagahashi
Atsushi
A
Hyono
Hiroyuki
H
Ohshima
D000162:Acoustics / Q000295:instrumentation; D003102:Colloids; D055664:Electrochemical Techniques / Q000295:instrumentation / Q000379:methods; D017136:Ion Transport; D008823:Micelles; D019999:Pharmaceutical Solutions / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*; D014465:Ultrasonics; D014732:Vibration; D014867:Water / Q000737:chemistry*
D003102:Colloids; D008823:Micelles; D019999:Pharmaceutical Solutions; D013501:Surface-Active Agents; D014867:Water