New aspects of the behaviour of alkyltrimethylammonium bromide micelles : light scattering and viscosimetric studies

S.J. Candau , E. Hirsch , R. Zana

Micellar solutions of dodecyl-, tetradecyl- and hexadecyl-trimethylammonium bromides (DTAB, TTAB and CTAB, respectively) have been investigated in H2O-0.1 M KBr by means of viscosity and elastic and quasielastic light scattering, from the dilute range (near the critical micellization concentration, CMC) to the semi-dilute range (up to 0.42 M). The DTAB micelles have been shown to be spherical in the whole concentration range, whereas TTAB micelles remain spheroidal up to about 0.2 M then become increasingly anisodiametric (probably with an elongated shape) as the concentration is increased. The CTAB micelles are already prolate at the CMC (axial ratio of about 6) and grow very rapidly in size with the surfactant concentration. The behaviour of the CTAB solutions at concentration above 4 x 10-2 M, that is in the range where the prolate micelles are probably entangled, has been found to follow power laws, just like solutions of entangled polymer chains in the semi-dilute range. The exponents characterizing the change of the diffusion coefficient and of the intensity of scattered light are 0.75 and — 0.25, respectively, in excellent agreement with the prediction of the theoretical treatments for semi-dilute polymer solutions. The viscosity data however show the limits of applicability of this model to the micellar systems investigated. Previous results concerning TTAB micelles in H 2O-0.1 M KBr in the presence of 1-pentanol have been reexamined.

Mots clés: colloids; diffusion in liquids; light scattering; organic compounds; viscosity of liquids

Domaines: Articles anciens

S.J. Candau, E. Hirsch, R. Zana. New aspects of the behaviour of alkyltrimethylammonium bromide micelles : light scattering and viscosimetric studies. Journal de Physique, 1984, 45 (7), pp.1263-1270. ⟨10.1051/jphys:019840045070126300⟩. ⟨jpa-00209863⟩