Synthesis and properties of multiarmed geminis

Three families of multiarmed and multicationic gemini surfactants, having p entaerythritol, dipentaerythritol, or adamantane cores, were synthesized an d examined for their colloidal properties in water. Geminis with four or si x six-carbon chains are highly water-soluble and do not self-assemble. But surface tension and conductivity measurements show that the geminis with fo ur or six eight-carbon chains form micelles in the 3-6 mM range (compared t o 0.5 M for a corresponding surfactant with a single chain). According to d ynamic light scattering, these micelles are small (<30 Angstrom diameter); no evidence of dendritic growth below 25 mM is evident. Geminis with four o r six 12-carbon chains are too water-insoluble to examine for micelle forma tion. It is concluded the outward projection of the hydrocarbon chains in w ater greatly enhances the propensity of the surfactants to self-assemble. M icellar growth is seemingly restricted by chain pairing, chain looping, and associative ring formation. Since;the aggregates have, despite these effec ts, greater residual water-hydrocarbon contact than found in typical micell es, water solubility of surfactants having longer chains is impaired.