Determining the Critical Micelle Concentration of Surfactants by a Simple and Fast Titration Method

Abstract

Critical micelle concentration (CMC) is a crucial parameter of widely used surfactants, and many methods have been developed for CMC determination. However, the current methods for CMC determination, such as conductive, surface tension, and fluorometric methods, are tedious and time-and sample-consuming because a series of samples with different concentrations of surfactants need to be prepared and measured. Although an economical, simple, and fast titration method for CMC determination (only one sample and several minutes are needed) was reported using changes in the color/fluorescence of ionic organic dyes, it has not been used in practical CMC determination owing to the disadvantages of these dyes: very narrow application range (only suitable for cationic or anionic surfactants) and difficult to identify titration end point, especially using different concentrations (10−300 μM) for the same kind surfactants. Here a C6-unsubstituted tetrahydropyrimidine (THP-T1) was found to possess unique and excellent characteristics in titrated surfactant solutions: above CMC, preferring to dissolve in micelles and showing no emission, and not until near/at CMC, being released from micelles and instantly forming aggregates with strong fluorescence. The fluorescence-turn-on change at CMC (titration end point) is so sensitive that it can be clearly observed without comparison of blank and control of dye concentration, and the concentration (c′ THP ) of THP-T1 in titrated solution at CMC is only about 1 μM for zwitterionic surfactants and 2.5 μM for other kinds of surfactants. The CMC values determined by the THP-T1-based titration method are almost the same as those determined by the fluorometric method using THP-T1 as probe. THP-T1 overcomes the disadvantages of reported dyes for CMC titration and realizes the economical, simple and fast CMC titration of different kinds of surfactants for the first time.

Effects of Different Stabilizers on Miniemulsion Methyl Methacrylate Polymerizations

“…[35] which makes calculation of micelles concentration in complex mixtures difficult. [39][40][41] It is known, however, that CMC values tend to increase with the hydrophilic nature of the surfactant and that nonionic surfactants that are insoluble in water may not generate micelles at all, especially in presence of a dispersed organic phase. [42] Some CMC values are reported by the respective stabilizer manufacturers, as described in the section that describes the manipulated materials.…”

Responsive drop method: quantitativein situdetermination of surfactant effectiveness using reconfigurable Janus emulsions

“…of chemical (fluorescent) probes, the need for expensive and/or complicated equipment, requirement of additional computational add-ons, and/or methods are time-and sample-consuming because a series of surfactant solutions with different concentrations must be prepared and characterized individually. [8][9][10][11] The development of novel responsive and triggerable materials combined with advances in imaging techniques hold promise to provide alternative cost-effective, rapid, and material gentle pathways for visualizing detectable changes of physical parameters in surfactant solutions and thus to circumvent complications associated with conventional techniques. In this context, liquidliquid transduction schemes, such as oil-in-water emulsions are appealing because they allow the investigation of surfactants within their designated environment.…”

Influence factors on the critical micelle concentration determination using pyrene as a probe and a simple method of preparing samples

“…The characteristics of THPscompletely no emission in surfactant micelles but strong AIE in dilute surfactant solutions-let us develop them as unique sensitive and visible fluorescence-turn-on (showing the strongest fluorescence at CMC) probes for CMC (the reported CMC probes based on fluorescence intensity change show fluorescence-turn-off change at CMC, that is, show the weakest fluorescence at CMC) [26,27]. Recently, we found that one of the THPs could be used as an excellent indicator for CMC titration and realized simple, sample-and time-saving CMC titration for different kinds of surfactants for the first time [28].…”