Conductivity, A Simple Method to Probe Micellar Solutions

Abstract

A conductivity experiment on the tetradecyltrimethylammonium X-benzoate surfactants and the corresponding sodium X-benzoate salts demonstrates how this physical property can be applied to the study of the complex equilibria of ionic micellar aggregates. The surfactant CMC and fractional ionization constant (alpha) values are determined from the conductivity measurements. A student class studies the surfactants, in which a number of substituted benzoate counterions are utilized, and can be introduced to Quantitative Structure-Activity Relationships (QSAR) to explain the resulting CMC values. High quality data can be recorded with ease. The data from a student class illustrate that CMC values are sensitive to the hydrophobicity of the X-benzoate anion. However, hydrophobicity is not the only important parameter to be considered. The student class can propose other important factors with some additional reading of the colloidal literature.

Scrutinizing Self-Assembly, Surface Activity and Aggregation Behavior of Mixtures of Imidazolium Based Ionic Liquids and Surfactants: A Comprehensive Review

“…But after the micelle formation, the rate of increase in conductivity decreases because the formed micelles have lower mobility than the distinct monomeric surfactant molecules that were present before. Thus, a breakpoint arises in the line and the concentration of surfactant corresponding to this breakpoint gives the value of CMC (Bachofer, 1996 ; Jungnickel et al, 2008 ; Ali et al, 2014 , 2016 ; Chauhan and Sharma, 2014 ). This method can also be utilized to determine the value of the degree of counterion dissociation as well as various thermodynamic parameters of micellization.…”

Simple Spectrophotometric Method to Measure Surfactant CMC by Employing the Optical Properties of Curcumin’s Tautomers

“…The values of the CMC can be determined by measuring the change of physicochemical properties that can occur in the solution due to micelle formation. A variety of physicochemical properties have been exploited for the determination of the CMC such as viscosity, − conductivity, − surface tension, − refractive index, , and light scattering. − …”

“…Students should be able to learn theoretical knowledge and apply experiments using different techniques in order to detect the CMC. Several educational papers related to this subject have been published, illustrating a variety of approaches to determine the CMC, including UV–vis spectroscopy, ,, fluorescence spectroscopy, , electrical conductivity, − surface tension, and contact-angle measurements …”

Examination and Improvement of Undergraduate Laboratory Experiment: Thermodynamics of a Surfactant Micellization

“…The experiment of CMC determination in the undergraduate course is straightforward, and several methods can be applied, which have been reported in this Journal , including the maximum bubble pressure method, the Wihelmy plate method, the drop volume method, drop–weight method, contact-angle, UV–visible absorption spectroscopy, fluorescence spectroscopy method, capillary rise, conductivity, and so on. − The ITC method is emphasized in this paper since ITC is a general technique that provides a complete and accurate thermodynamic description of association processes in complex systems such as surfactant aggregation in colloidal systems. , …”