Study On Molecular Aggregates Of N-(1,1-Dihydroperfluoroalkyl)-N,N,N-Trimethylammonium Chloride

Dissolution into water of solid fluorinated cationic amphiphiles was investigated in detail for four amphiphiles with different alkyl chain lengths: N-(1,1-dihydroperfluorooctyl)-, N-(1,1-dihydroperfluorodecyl)-, N-(1,1-dihydroperfluorododecyl)-, and N-(1,1-dihydroperfluorotetradecyl)-N,N,N-trimethylammonium chloride. The dissolution seemed quite fast just from appearance, but it took a very longtime to reach thermodynamic dissolution equilibrium, where a specific conductance of the solution steadily increased with time even after the solid particles perfectly disappeared from the solution. Change in sizes of molecular aggregates with time was confirmed by dynamic light scattering, and the distribution of sizes decreased with time and with increasing temperature. The critical micelle concentrations (cmc's) were determined from the specific conductivity change against concentration, after the dissolution equilibrium was reached. The cmc of the latter two amphiphiles monotonically increased with temperature, and the Gibbs energy contribution per CF2 group to micellization was 1.54 times as large as that per CH2 group from the slope of the plots of ln(cmc) against the carbon number of the alkyl chain. The rate of dissociation of micellar aggregates to monomers was traced by electric conductivity on an oscilloscope screen, and the activation energy obtained from its temperature dependence was found to decrease with increasing alkyl chain length. Taking all experimental results into consideration, the processes from the solid state to aggregates in the dissolved state in thermodynamic equilibrium were proposed.