Simplified Method for the Determination of Critical Micelle Concentration

M. J. L. CASTRO, H. RITACCO, J. KOVENSKY AND A. FERNÁNDEZ CIRELLI

JOURNAL OF CHEMICAL EDUCATION

Division of chemical education of the American chemical society

Lugar: Washington DC; Año: 2001 vol. 78 p. 347 - 348

0021-9584

Surfactants are versatile compounds with a wide range of applications in soaps, detergents, pharmaceuticals, motor oils, and as membrane mimics; they may also be useful in chemistry for kinetic studies, among other uses. Surfactants are amphiphilic molecules composed of a hydrophobic part and a polar "head" group. A long hydrocarbon chain usually constitutes the hydrophobic moiety, while the hydrophilic head can be either an ionic or a polar nonionic group. In water, surfactant molecules arrange themselves into organized molecular assemblies known as micelles. The concentration above which this phenomenon occurs is called the critical micelle concentration (cmc). The value of the cmc can be determined by the change in the physicochemical properties of the surfactant solutions as the concentration of the amphiphilic molecules is increased. Several experiments have been reported to familiarize undergraduate students with micellar solutions and with techniques to measure the cmc (1?4). A method using fluorescein and cetyl trimethyl ammonium bromide has been reported (1, 2). The effect of charge association between cationic micelles and fluorescein dianion can be analyzed by fluorescence, but this technique requires the availability of a fluorometer for cmc determination. The drop-weight method based on Tate?s law (3) is a simple method for cmc determination. However, its simplicity is handicapped by the requirement of correction factors, not always available, for quantitative determination. Moreover, it seems difficult to achieve the very slow formation of drops that is necessary to obtain accurate results by the experimental procedure proposed. simple method for cmc determination. However, its simplicity is handicapped by the requirement of correction factors, not always available, for quantitative determination. Moreover, it seems difficult to achieve the very slow formation of drops that is necessary to obtain accurate results by the experimental procedure proposed. association between cationic micelles and fluorescein dianion can be analyzed by fluorescence, but this technique requires the availability of a fluorometer for cmc determination. The drop-weight method based on Tate?s law (3) is a simple method for cmc determination. However, its simplicity is handicapped by the requirement of correction factors, not always available, for quantitative determination. Moreover, it seems difficult to achieve the very slow formation of drops that is necessary to obtain accurate results by the experimental procedure proposed. simple method for cmc determination. However, its simplicity is handicapped by the requirement of correction factors, not always available, for quantitative determination. Moreover, it seems difficult to achieve the very slow formation of drops that is necessary to obtain accurate results by the experimental procedure proposed. A method using fluorescein and cetyl trimethyl ammonium bromide has been reported (1, 2). The effect of charge association between cationic micelles and fluorescein dianion can be analyzed by fluorescence, but this technique requires the availability of a fluorometer for cmc determination. The drop-weight method based on Tate?s law (3) is a simple method for cmc determination. However, its simplicity is handicapped by the requirement of correction factors, not always available, for quantitative determination. Moreover, it seems difficult to achieve the very slow formation of drops that is necessary to obtain accurate results by the experimental procedure proposed. simple method for cmc determination. However, its simplicity is handicapped by the requirement of correction factors, not always available, for quantitative determination. Moreover, it seems difficult to achieve the very slow formation of drops that is necessary to obtain accurate results by the experimental procedure proposed. association between cationic micelles and fluorescein dianion can be analyzed by fluorescence, but this technique requires the availability of a fluorometer for cmc determination. The drop-weight method based on Tate?s law (3) is a simple method for cmc determination. However, its simplicity is handicapped by the requirement of correction factors, not always available, for quantitative determination. Moreover, it seems difficult to achieve the very slow formation of drops that is necessary to obtain accurate results by the experimental procedure proposed. simple method for cmc determination. However, its simplicity is handicapped by the requirement of correction factors, not always available, for quantitative determination. Moreover, it seems difficult to achieve the very slow formation of drops that is necessary to obtain accurate results by the experimental procedure proposed.