The Critical Micelle Concentration for Aqueous Tetradecyl

Determination of the Critical Micelle Concentration for Aqueous Tetradecyl Trimethyl Ammonium Bromide using UV-Vis Spectroscopy Overview: Surfactants such as tetradecyl trimethyl ammonium bromide (TTABr) can form micelles in aqueous solutions when exceeding the critical micelle concentration (CMC, see the figure below). It has a non-polar chain with a polar head, forming a micelle in water (polar head on its surface). We will use UV-Vis spectroscopy to determine the CMC of TTABr by adding 1-Benzoylacetone (BZA). Below the CMC, dilute amounts of 1-Benzoylacetone (BZA) will absorbs light at λ = 250 nm (no micelles). Upon micelle formation, BZA will tautomerize to the enol which absorbs light at λ = 312 nm (micelles present) caused by intermolecular hydrogen bonding (J. Chem. Educ., 74, 1997, 1227-1231). In this lab, we will observe the changes in the absorbance measurements at these two wavelengths caused by varying the concentration of the TTABr surfactant. This lab will be conducted as a class with an emphasis on the Pre-Lab, lab notebook recording, basic analysis of results, and basic report writing. Instrumentation: UV-vis spectroscopy Chemicals and Materials needed: Tetradecyl Trimethyl Ammonium Bromide (TTABr), 1-Benzoylacetone (BZA), dioxane stock solution, micropipettes, Deionized water (from squeeze bottle), mass balance Introduction Links: See Canvas for links for theory (J. Chem. Educ., 74, 1997, 1227-1231) Assignment Deliverables: Post-Lab Assignment (on Canvas)