NOVEL GEMINI MICELLES FROM DIMERIC SURFACTANTS WITH OXYETHYLENE SPACER CHAIN - SMALL-ANGLE NEUTRON-SCATTERING AND FLUORESCENCE STUDIES

Three new gemini surfactants containing mono-, di-, and trioxyethylene spacer chains have been synthesized. Small angle neutron scattering ( SANS) cross sections from the micellar aggregates of these dimeric amp hiphiles Br-, C16H33NMe2+-CH2(CH2OCH2)(p)CH2-N+Me2-n-C16H33,Br-, (wher e p = 1, 2, and 3) in aqueous media (D2O) have been measured. The data have been analyzed using the Hayter and Penfold model for macro-ion s olution to compute the interparticle structure factor S(Q) taking into account the screened Coulomb interactions between the dimeric micelle s. The SANS analysis showed that the micellar morphology depends on bo th the nature and the length of the spacer unit. Detailed analysis of the data further indicates that the introduction of oxyethylene spacer is not sufficient enough to prevent looping of the spacer chain. Thus the average separation between the dimethylammonium ion headgroups is considerably lower than is expected from a fully extended conformatio n of the spacer chain. The micelles from these surfactants have also b een characterized in terms of their critical micelle concentrations (c mc), microviscosities, and micropolarities on the basis of the informa tion provided by micelle-solubilized fluorescent probes. These results indicate little difference in their micellar properties such as cmc, microviscosity, and micropolarity.