Determination of Critical Concentrations of Self-Organization of Sodium Octanoate in Aqueous Solutions Using Raman Spectroscopy
Recently, surfactants are actively used for the synthesis and modification of nanoparticles in nanotechnologies, in nanomedicine (drug delivery), which necessitates contactless diagnostics of technological media or biotissues together with surfactants present in them. Diagnostics means determining the main characteristics and state of the components of these media, including surfactants. The main characteristics of surfactants in solution are the following: first critical micelle concentration (CMC1), at which spherical surfactant micelles begin to form in the solution, critical concentration of transformation of spherical micelles into non-spherical micelles (second critical micelle concentration (CMC2)), and critical premicelle concentration (CPMC), when the first associates (dimers) begin to form in the solution.
Raman spectroscopy method made it possible to obtain the values of critical concentrations (CMC1, CMC2 and CPMC) of self-organization of sodium octanoate in aqueous solutions. The results were compared with the results of absorption spectroscopy in the near infrared region, pH-metry, measurements of the conductivity and surface tension of solutions, as well as with literature data. Analysis of the data showed that the method of laser spectroscopy allows not only determining the values of critical concentrations with an accuracy no worse than the common contact methods, but also provides information about the conformation of hydrocarbon radicals of the amphiphile (octanoate anion) and about the intermolecular interactions of water molecules in surfactant solutions.
I. V. Plastinin
Moscow State University, Moscow, 119991
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