Gemini surfactants with short linkers: thermodynamics of Micelle formation

Abstract

AbstractWe have been investigating the physical properties of simple Gemini surfactant with short linker chains using conductivity, dynamic light scattering (DLS) and isothermal titration calorimetry (ITC). The surfactants used here have the general formula (CH3(CH2)11)(CH3)2-N+-(CH2)n-N+(CH3(CH2)11)(CH3)2·Br2, where n = 2, 3 or 4 and, as such, are designated as 12-2-12, 12-3-12 and 12-4-12. The ultimate goal of this work was to determine the enthalpy of demicellization using ITC. To determine the proper experimental conditions, it was necessary to first determine the critical micelle concentration (cmc) using conductivity and the size of the formed micelles using DLS for each surfactant. The results indicate a number of linear relationships between the number of carbons in the linker and certain physical properties such as cmc and ΔGmic as determined by conductivity studies. As expected, demicellization is enthalpically unfavorable but entropically driven. Linear relationships are also observed between the number of linker carbons and some thermodynamic properties as determined by ITC. Graphical abstract