Tuesday, October 14 | 11:00 a.m. - 12:00 p.m.
Classroom Building 170 

Counterion Effects on the CMC of Cationic Gemini Surfactant Micelles

The gemini surfactant, pentadiyl-α,ω-bis(dimethyldodecylammonium bromide), referred to as 12-5-12 with added sodium benzoates and cinnamates was studied measuring critical micellization constant (CMC) values by four different methods. Since the CMCs represent the thermodynamic parameter for the formation of micellar aggregates, it demonstrates the influence of the counterions on micelle formation. The resulting CMC values are related to the hydrophobicity of the anions. The nine counterions in this research are benzoate, four ortho-halogenated benzoates, 3,5-difluorobenzoate, cinnamate, 3,5-difluorocinnamate, and sorbate. The four methods, conductivity, fluorescence intensity, NMR chemical shift and isothermal titration calorimetry, were employed to obtain CMC and the ΔH of micellization. Detailed analysis of the 1D and 2D NMR spectra yield data on the counterion binding to micellar interface. A correlation of the Log (CMC) values and the Log P values of the organic acid which deprotonated to serve as the counterions demonstrate the Log P values can be utilized to predict the surfactant aggregation behavior over an extensive range. These stoichiometric mixtures are useful as chemist and chemical engineers attempt to employ various surfactants with organic counterions as newer ionic liquids.

About the Speaker

Steven Bachofer obtained B.Sc. in Chemistry from the University of the Pacific in 1979.  In 1983, he received his Ph.D. in Inorganic Chemistry from the Brown University, Rhode Island. He worked as a Research Scientist in Clorox Company (1983-1987),). Dr. Bachofer joined Saint Mary’s College of California in 1988, and as a Visiting Researcher at Rutgers University (2010) Dr. Bachofer has studied cationic surfactants to understand the subtle forces controlling the micellar aggregate formation and shape. Cationic surfactants with select benzoate counterions form elongated wormlike micelles and these aggregates are considered living polymers. This research involves physical property and NMR spectroscopic determinations. More recently, the research has included isothermal titration calorimetry and collaborations on molecular dynamic simulations.  Separately, teaching the Environmental Chemistry has led to doing a number of experiments using field portable XRF instrumentation and developing educational experiences benefiting community partners.