Synthesis and Properties of Multiarmed Geminis.
Three families of multiarmed and multicationic gemini surfactants, having pentaerythritol, dipentaerythritol, or adamantane cores, were synthesized and examined for their colloidal properties in water. Geminis with four or six six-carbon chains are highly water-soluble and do not self-assemble. But surface tension and conductivity measurements show that the geminis with four or six eight-carbon chains form micelles in the 3-6 mM range (compared to 0.5 M for a corresponding surfactant with a single chain). According to dynamic light scattering, these micelles are small (<30 Å diameter); no evidence of dendritic growth below 25 mM is evident. Geminis with four or six 12-carbon chains are too water-insoluble to examine for micelle formation. It is concluded the outward projection of the hydrocarbon chains in water greatly enhances the propensity of the surfactants to self-assemble. Micellar growth is seemingly restricted by chain pairing, chain looping, and associative ring formation. Since the aggregates have, despite these effects, greater residual water-hydrocarbon contact than found in typical micelles, water solubility of surfactants having longer chains is impaired.
Menger
Fredric M.
FM
Department of Chemistry, Emory University, Atlanta, Georgia 30322.
Migulin
Vasily A.
VA