Small angle neutron scattering of direct micelles in binary and ternary surfactantÈalcoholÈ surfactantÈD 2 O systems has been measured. The nonionic surfactant was poly(oxyethylene-23) lauryl ether D 2 O (C 12 E 23, commercial name : Brij 35) which was used at concentrations far beyond its critical micellar concentration : between 0.1 and 15 mass% (about 1.0 ] 10~3È1.5 ] 10~1 mol l~1). The alcohols were butan-1-ol, pentan-1-ol, hexan-1-ol, and heptan-1-ol at concentrations of about 0.25 mol l~1. The spectra could quantitatively be modelled by the PercusÈYevick integral equation method in combination with a core/shell model yielding detailed information about the size, the (ellipsoidal) shape, the aggregation number, the internal structure and the distribution of the micelles. The ternary systems were modelled with an additional parameter, the partition of the alcohol between the outer aqueous bulk and the inner micellar pseudo-phase. In the case of the pentanol system the partition coefficient inferred from NMR self-di †usion measurements was used to describe the scattering result.

The kinetics of enzyme catalyzed alcohol oxidation has been measured in liquid water/ethanol/Brij 35 and water/1-pentanol/Brij 35 systems, essentially in the water-rich regions. For the ethanol systems it was found that the enzymatic activity sharply decreases with increasing alcohol concentration independently of the surfactant concentration between 0 and 22 mass %. In the case of the 1-pentanol systems the enzymatic activity decreases also with increasing alcohol concentration, but this decrease can considerably be attenuated by adding increasing amounts of surfactant. To explain these results at the nanometer level, small-angle neutron scattering (SANS) experiments have been carried out on these systems. The comparison of the scattering and the kinetic measurements suggests the following interpretation. In all cases, the enzymatic activity depends on the concentration of the alcohol in the aqueous phase or in the aqueous pseudophase containing the enzyme. A certain amount of alcohol may be present in an organic pseudophase formed by direct micelles. In the case of the 1-pentanol systems the alcohol participates in the structuration of the micelles and is concentrated in the micelles, whereas in the case of the ethanol systems the alcohol remains essentially in the aqueous pseudophase and even destroys the micelles. These results suggest that in some cases enzymatic activity can be used as a probe to detect some aspects of the molecular organization of a complex liquid.

From a thorough study of many systems incorporating water, the ionic surfactant sodium dodecylsulfate, straighter or branched alkanols and aliphatic or aromatic hydrocarbons, it clearly appears that the molecular structure of the alkanol used as the cosurfactant is the composition factor that primarily determines the configuration of the microemulsion domain and, correlatively, the type of the microemulsion electroconductive and viscous behavior.Key words: Microemulsion(s), phase diagram(s), viscosity, electrical conductivity, water, sodium dodecylsulfate, straight alkanol(s), branched alkanol(s), aliphatic hydrocarbon(s), aromatic hydrocarbon(s).The realms-of-existence of monophasic, stable, fluid, transparent and isotropic media, (so-called "microemulsions" [1]), were delineated, at T = 25 ~ for a great number of systems incorporating water, sodium dodecylsulfate, straight or branched alkanols with number of carbons ranging from 2 to 10, and aliphatic, (n-octane, n-dodecane, n-hexadecane), or aromatic, (benzene, toluene), hydrocarbons. It has thus been possible to evidence the influence of different composition factors upon the general configuration of the microemulsion domain, e. g. straight alkanol number of carbons, alkanol isomery, aliphatic hydrocarbon chain-length, and aliphatic hydrocarbon-aromatic hydrocarbon substitution [2][3].It clearly appears from this study that, in any case, the three-dimensional microemulsion domain is the volumic extension of the realm-of-existence of the water/surfactant/alkanol micellar solutions. The micro-1) Present addresses: A. Zradba, Ecole Normale Sup~rieure de Casablanca, Avenue Victor Hugo, Casablanca, Maroc (Morocco).L. Nicolas-Morgantini, L'Or~al, 1, Avenue Saint Germain, 93600 Aulnay-sous-Bois (France). W950emulsion domain configuration is influenced, primarily, by the alkanol molecular structure, and, to a lesser degree, by that of the hydrocarbon. As a general rule, the microemulsion domain existing in the phase tetrahedron of systems incorporating long straight alkanols, (number of carbons no1 > 6), appears to consist of two disjoined volumes, V1 and V2, respectively built on the regions L1 and L2 corresponding, in the water/ surfactant/alkanol phase diagram, to direct and inverse ternary micellar solutions. Per contra, the microemulsion domain of systems incorporating short straight alkanols, (nc~ < 3), forms in the phase tetrahedron an all-in-one-block volume built on the "monophasic" area that exists in the water/surfactant/alkanol phase diagram, as the result of the merging of the L1 and L2 regions. In the case of medium straight alkanols, (3 < nca < 6), the microemulsion domain also forms an allin-one-block volume but exhibits configuration irregularities that reflect peculiarites of the water/surfactant/alkanol "monophasic" area.For the four systems water/sodium dodecylsulfate/ C4 to C7 straight alkanols/n-dodecane, details of the microemulsion domain configuration were obtained from systematic determinations of the microemulsion

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