Evaluation of Non‐Ambiguous Critical Micelle Concentration of Surfactants in Relation to Solution Behaviors of Pure and Mixed Surfactant Systems: A Physicochemical Documentary and Analysis

Abstract

Critical micelle concentration (CMC) is a fundamental physical parameter of surfactant aggregation in solution. The CMC is determined by different methods, tensiometry, conductometry, microcalorimetry, fluorimetry, and so on. However, it is known that though CMC is reported as a single value, in reality, micelle formation occurs over a narrow range of concentration for different experimental procedures produce different results. We shall discuss about a unique procedure of measuring correct CMC applicable to all potential methods used in practice. This is essential for the evaluation of thermodynamic properties of the micelle forming process in pure and mixed states in terms of solution theories. As we in this short documentary want to deal with various aspects of Milton Rosen's research-wherein we have also worked-a few other facets of surfactant chemistry research, besides the micelle formation, are also briefly discussed. In mixed surfactant systems, synergistic effects in various surfactant properties like detergency, foaming, solubilization, and so on are found whereas in some others non-synergistic effects are observed. Dehydration of micelles with an increase in temperature or by the addition of hydrophilic substances may cause clouding to the system. Soluble amphiphilic systems produce Gibbs monolayer at the air/water interface; insoluble amphiphiles form Langmuir monolayers.A documentary of the above aspects will be herein presented and discussed. We mention that this article is neither an original research article nor a review article. This is a mixture of the two: a documentary of both original research and some review of our works presented in memory of Prof. Milton Rosen.

A Surfactant Concentration Model for the Systematic Determination of the Critical Micellar Concentration and the Transition Width

“…The authors also compare the concentrations of free and bound counterions, determined in ion-selective-electrode (ISE) experiments, with those calculated with the concentration model Equations ( 7) and (12). They find good agreement at low PS content but deviations at PS rich mixtures.…”

“…It is principally an impossible task to define or to determine a coherent cmc value from these nonlinear properties as long as the intrinsic parameters are not taken into account. This applies to procedures analysing derivatives of first, second, third or even higher orders of the experimental data, but also to graphical methods looking for intersections of straight lines [ 10 , 11 , 12 ]. As said before, the critical micellization concentration, cmc , is a property of the surfactant concentration itself, not of other derived experimental properties.…”

“…Figure 2 shows the results of the global fit of Equation (12) to the whole dataset of ClMP and Figure A1 to that of IMP. The fit was performed with a commercial software (Origin Pro).…”

“…Any property of the surfactant solution affected by the formation of micelles can in principle be used to determine the cmc : electrical conductivity of ionic surfactants, surface tension, NMR chemical shift, UV-Vis absorption, fluorescence spectroscopy of a probe molecule, ion-selective electrodes, isothermal titration calorimetry, densimetry, ultrasound spectroscopy, translational diffusion determined by light scattering or fluorescence correlation spectroscopy and many more. Many methods for the definition and determination of the cmc from property-concentration plots have been proposed over the last 70 years [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ] and are still published [ 10 , 11 , 12 ]. Most of these methods determine the cmc from the intersection of two straight lines drawn or fitted to the two branches below and above the cmc , assuming that the property depends linearly on the concentrations of free surfactant and micelles.…”

Special Issue Honoring Professor Milton Rosen

“…Rosen's work on structure property relations and surfactant synergy are highlighted in two review articles. Naskar et al (2021) present an unambiguous method for determining critical micelle concentration (CMC) using derivative plots and use the values obtained to calculate surfactant synergy using the Rubingh and Rosen approach. Interaction parameters are discussed in relation to detergency, foaming, solubilization, and cloud point.…”