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Much is known about the formation of micelles from amphiphilic molecules and ions. Interaction of amphiphiles at less than Critical Micelle Concentration (cmc) is less well understood. Our research strategy was to make use of the cyclic voltammetry (CV) technique and measured viscosity to determine the ionic radii of Sodium Dodecyl Sulfate (SDS) structures in solution. The manner in which the measured diffusion coefficients and ionic radii change with respect to amphiphile concentration was of interest. Our strategy was centered upon four considerations. First, Ferrocene (Fc) was used as an electrochemical marker for amphiphile aggregate formation. Ferrocene should interact with the hydrophobic portions of the amphiphile structures. The concentration ratio of SDS to Fc was maintained around 240 to ensure one Fc per amphiphile moiety. Second, the solubility of Fc in deionized water was obtained as evidence of Fc interaction with SDS. It was anticipated that Fc solubility would be much smaller when the solution contained no amphiphile. Third, after demonstrating electrochemical reversibility, the Randles-Sevcik equation was used to calculate the Fc-SDS diffusion coefficient. Finally, from the measured solution viscosities and diffusion coefficients the ionic radii were computed from the Stokes-Einstein equations. Our results showed a definite deviation from normal micellar behavior at concentrations much less than cmc which will further help to understand the behavior of amphiphiles at concentrations less than the cmc.

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Robert G. Keil

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Stander Symposium poster


This poster reflects research conducted as part of course project designed to give students experience in the research process.

Research exercise: Solution Structures of Amphiphiles