Critical micelle concentration empirical

Estimation is easier and less time-consuming because use is made of empirical relationships between the BCF and physicochemical properties of the compound, such as water solubility (S) [42-48], Km, (solid organic carbon/water partition coefficient) [48], Kmw (membrane water partition coefficient), iipw (liposome water partition coefficient) [49], critical micelle concentration (CMC) [45], steric factors, molecular weight [47,48], and others. The most common regression method is the estimation of BCF from the octanol-water partition coefficient (Kovl) [18,42,44-48,50,51],... 

The experimentally derived empirical expressions used in models such as the mass-action framework have contributed greatly to the logical selection of surfactants for efLcient and effective solubilization of drugs. However, there is currently a need to develop more efLcient, less toxic surfactants for use in drug delivery. A model that is able to provide quantitative prediction of the critical micelle concentration and micelle size without the need for extensive experimental measurements would greatly accelerate the development of novel surfactant chemistries for use in pharmaceutical applications. 

The value of the critical micelle concentration depends on a large number of parameters. Usually the more surface active the amphiphihc monomer, the higher is the tendency for micellization and, hence, the lower the CMC of the micelle produced. Accordingly, the longer the total carbon chain length of the monomeric surfactant, the lower the CMC becomes. The number of carbon atoms, n, is empirically related to the logarithm of the CMC ... 

The optimum concentration of surfactant for maximum foam effectiveness has to be determined empirically. It is often of the order of about 0.1 -0.3 mass% active surfactant. A useful starting point for preparing and/or testing foams is a surfactant concentration that is 1.5 - 2 times the value of the critical micelle concentration (cmc). 

Elevens Constants. The empirical parameters in an equation advanced by Elevens for predicting the critical micelle concentrations (cmc) of surfactants in terms of the number of carbon atoms in the hydrocarbon chain. Elevens constants for numerous surfactants are tabulated in references [17, IS]. 

In the very early phase of the kinetic studies on the effects of [micelles] on the reaction rates, it has been observed that an empirical kinetic equation similar to Equation 7.48 with replacement of [M X ] by [Smflj - CMC (where [Smflj and CMC represent total surfactant concentration and critical micelle concentration, respectively) is applicable in many micellar-mediated reactions. But the plots of kobs vs. ([Surf]j - CMC) for alkaline hydrolysis of some esters reveal maxima when surfactants are cationic in nature. - - Similar kinetic plots have also been observed in the hydrolysis of methyl orthobenzoate in the presence of anionic micelles. Bunton and Robinson suggested a semiempirical equation similar to Equation 7.49, which could explain the presence of maxima in the plots of ko s vs. ([Surflj - CMC). In Equation 7.49), J, is an empirical constant. 

The hypothesis of an aggregation of surfactants into micelles at concentrations in excess of the critical micelli-zation concentration of the surfactant is old (McBain, Laring and Titlay, 1919 Jones and Bury, 1920 and Ekwall, 1927). The phenomenon can be empirically understood in the following manner. 

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