MICELLAR PROPERTIES AND STRUCTURE OF BENZETHONIUM CHLORIDE IN ISOTROPIC AQUEOUS-SOLUTIONS

The micellar structure of the cationic surfactant benzethonium chlorid e (BZCl) was analysed by small-angle x-ray scattering techniques. The shape, size and characteristics of the internal structure of BZCl was studied by the contrast variation method at 20-degrees-C (CMC = 5.35 x 10(-4) Mol/l) by changing the electron density of the solvent through addition of polyols, e.g. sucrose or glycerol. The obtained scatterin g data were converted to absolute intensities, and analysed for interm icellar interference effects, by applying the rescaled mean spherical approximation method. The morphological parameters, micellar volume, a verage electron density, rho1BAR, radius of gyration, R(v), second mom ent of the electron density distribution, ''a'', and square average of the electron distribution, (DELTArho1(2)), were determined from scatt ering data in the range of 0.001 < h < 0.08 angstrom-1. The apparent a ggregation number (65 +/- 10), degree of ionization (alpha = 0.15) wer e also determined by static light scattering. The micellar shape of BZ Cl was computed from R(v), and the maximum dimension of the micelle D( max) = 54.0 angstrom were obtained from the distance distribution func tion. The shape of the BZCl micelle is consistent with an oblate ellip soid -of revolution with a = 26.8 angstrom. The condensation effects o f the chloride ions on the BZCl was compared for the ''structural'' mo del vs. the ''effective model'' from static light scattering and x-ray scattering.The polydispersity in micellar size was found to be small, 1.55 in the weight-average molecular weight and 17% in [V1]. These va lues. including ([M(w,app)]), the one of the radius of gyration of the exclude volume (R(g) = 20.3 +/- 0.3 angstrom) are independent of the density of the solvent through addition of polyols.