Effect of spacer rigidity on the aggregations of ester containing Gemini surfactants in aqueous solutions: A study of density and fluorescence

The two Gemini surfactants (1-Dodecanaminium,N,N′-[[(2E)-1,4-dioxo-2-butene-1,4-diyl]bis(oxy-2,1-ethanediyl)]bis[N,N-dimethyl-,bromide)(12-fo-12) and (1-dodecanaminium,N,N′-[(1,4-dioxo-1,4-butanediyl)bis(oxy-2,1-ethanediyl)] bis[N,N-dimethyl-, bromide) (12-su-12), which have very similar structure but bearing rigid and flexible spacers respectively, and their monomeric counterpart 1-dodecanaminium, N-[2-(acetyloxy)ethyl]-N,N-dimethyl-, bromide (DTAAB) were synthesized and their aggregation behaviors in aqueous solutions were studied by measurements of the density and fluorescence. From the density measurements, the vesicle formation of 12-fo-12 was confirmed and the volumetric properties of the aggregates were obtained. By using fluorescence methods, the micropolarity, the steady-state anisotropy and the aggregation number in the micelles were measured. It was found that the rigidity of the spacer affected the microenvironmental properties significantly. The aggregation numbers were used to compare with those calculated from the geometric properties of the micelles by a simple geometry model, which showed good consistence with each other except for the calculations involving the surface area of the headgroup for the 12-su-12 system. It indicated that the surface area of 12-su-12 at the water–micelle interface was significantly larger than that at the water–air interface.