Pinacyanol spectrum

Figure9.8 The absorbance of 1.05 x 10 M pinacyanol chloride at 610.0 min pH 9.59 sodium borate buffer (I = 0.1) at 50 °C vs. dodecanoate concentration. The absorption spectrum of pinacyanol chloride in aqueous solution of anionic soaps changes sharply to one characteristic of its solutions in organic solvents within a small range of soap concentration (X ax 610 nm). This effect is attributed to the formation of micelles, in whose hydrocarbon-like layers or cores the dye is solubilized. The concentration of soap at which this spectral change occurs is taken as the cmc. The use of dyes for the determination of cmc values may lead to micelle formation at a concentration below the true cmc. In practice, the method gives only a rough approximation of the cmc. (Adapted, with some modifications, from Corrin et al., 1946.)...

The kinetic spectrum reveals more peculiar details than the usual spectral efficiency curve of the external photoeffect. For example, the kinetic spectra for pinakryptol and pinacyanol are quite different, whereas the efficiency curves are much alike.45... 

Various polymethine dyes (pinacyanol, pseudoisocyanine) are soluble in alcohol and acetone as well as water. In the first two solvents the spectrum does not change as the concentration is raised in these cases the dyes follow Beer s law. On the other hand if the solvent is water, important modifications take place in the spectrum (ScHEiBE et al ). These changes which are associated with a great rise of the viscosity, can best be explained by an association of the ions of the dye, first to double ions, later to polymolecular formations. 

To illustrate the changes in the spectrum on increase of the concentration the result of an experiment bij Scheibe with pinacyanol may be added (Fig. 45). The conductivity of these solutions does not charge so that the conclusion is drawn that there is association of the ions. In this medium — water — we must assume that the main spring in association are the Van der Waals forces between the aromatic... 

Change in the spectrum of pinacyanol on increase of the concentration (Scheibe, 1938). 

Dyes are often used for determining the critical micelle concentration of detergents. Their spectra may, however, be affected by concentrations of surfactants far below the CMC. One can readily see the effect on the spectrum of Pinacyanole of 0.1 ppm Nacconol NRSF, an alkylbenzene sulfonate. 

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