Study by light scattering of the effect of the surfactant chemical structure on micellar interactions of water/oil microemulsions (original) (raw)

Light-scattering investigations on dilute nonionic oil-in-water microemulsions

AAPS PharmSci, 2000

Dilute 3-component nonionic oil-in-water microemulsions formulated with either a polyoxyethylene surfactant (C 18:1 E 10 or C 12 E 10) or the alkylamine-N-oxide surfactant, DDAO (C 12 AO), and containing either a triglyceride or an ethyl ester oil have been examined using dynamic and static lightscattering techniques. Analysis of the results showed distinct differences in the tested oil's mode of incorporation into the microemulsion droplets, with both the molecular volume of the oil and the hydrophobic chain length of the surfactant being important. For example, microemulsions formulated by C 18:1 E 10 and containing one of the larger molecular volume oils (that is, either a triglyceride, Miglyol 812, or soybean oil) or the ethyl ester of fatty acid oil, ethyl oleate, exhibited first a decrease and then an increase in hydrodynamic size and surfactant aggregation number, suggesting that the asymmetric C 18:1 E 10 micelles became spherical upon the addition of a small amount of oil and grew thereafter because of further oil being incorporated into the core of the spherical microemulsion droplet. A similar conclusion of sphericity could not be drawn for microemulsions stabilized by C 18:1 E 10 and containing one of the oils smaller in molecular volume (namely tributyrin, ethyl butyrate, or ethyl caprylate) where neither the aggregation number nor the hydrodynamic radius changed much upon the addition of oil. This result suggested that these oils were preferentially located in the interfacial surfactant monolayer, behaving in much the same way as a cosurfactant. A different trend of results, however, was seen for microemulsions prepared

Light scattering study of oil-in-water microemulsions: corrections for interactions

Langmuir, 1987

A series of oil-in-water microemulsions formulated with 2% (w/v) cetyltrimethylammonium bromide as surfactant, 4% (v/v) 1-butanol as cosurfactant, and varying amounts of n-octane ( 0 4 % v/v) in three sodium bromide brines (I%, 1.5%, and 2% w/v) were studied by using quasielastic light scattering at 25 "C. Electrophoretic light scattering results were obtained for the 1% (w/v) NaBr microemulsions and have been used to correct the diffusion coefficients obtained from quasielastic light scattering for particle/particle interactions. The corrections for the 1 % (w/v) NaI3r system were found to be large, on the order of 50% at higher volume fractions. Naive use of the Stokes-Einstein formula relating the diffusion coefficient to the particle size results in a severe underestimation of the microemulsion droplet size. The combination of ELS and QELS data also makes it possible to estimate the degree of ionization of the surfactant head groups.

Influence of additives on the structure of surfactant-free microemulsions

Physical Chemistry Chemical Physics, 2015

We study the addition of electrolytes to surfactant-free microemulsions in the domain where polydisperse pre-Ouzo aggregates are present. As in previous studies, the microemulsion is the ternary system water/ ethanol/1-octanol, where ethanol acts as co-solvent. Addition of electrolytes modifies the static X-ray and neutron scattering, and dynamic light scattering patterns, as well as the position of the miscibility gap, where spontaneous emulsification occurs upon dilution with water. All observations can be rationalized considering that electrolytes are either ''salting out'' the ethanol, which is the main component of the interface stabilizing the aggregates, or producing charge separation via the antagonistic ion effect discovered by Onuki et al. Amphiphilic electrolytes, such as sodium dodecylsulfate or sodium dietheylhexylphosphate, induce a gradual transition towards monodisperse ionic micelles with their characteristic broad scattering ''peak''. In these micelles the ethanol plays then the role of a cosurfactant. Dynamic light scattering can only be understood by combination of fluctuations of aggregate concentration due to the vicinity of a critical point and in-out fluctuations of ethanol.

Toward surfactant-free and water-free microemulsions

Journal of Colloid and Interface Science, 2015

It was recently demonstrated that a nano-clustering was present in the monophasic ''pre-Ouzo'' region of ternary liquid mixtures without surfactants. The goal of this work is to check if this nano-clustering is also present in the surfactant-free and water-free ''green'' microemulsions glycerol/ethanol/1-octanol and deep eutectic solvent/tetrahydrofurfuryl alcohol/diethyl adipate. The deep eutectic solvents used instead of water were ethylene glycol-choline chloride (molar ratio 4-1) and urea-choline chloride (molar ratio 2-1). To our knowledge this is the first time that deep eutectic solvents were used to formulate microemulsions. The surfactant-free and water-free microemulsions were studied using phase diagrams, dynamic light scattering, and small-angle X-ray scattering. The presence of aggregate fluctuations was demonstrated and they were found to be independent of molecular critical fluctuations, except when approaching the critical point where the critical phenomenon is superimposed to the signal. These structures have similarities to classical microemulsions but, in contrast to them, without having a sharp interface between the non-miscible phases, much as it was the case for systems previously investigated like water/ethanol/oil, where the oil was 1-octanol, fragrance molecules, or mosquito repellents.

Effect of surfactant counterion on spectroscopic properties of water in oil microemulsions

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1996

The effect of replacing the Na + counterion of Aerosol OT by Cu 2+ on the hydration mechanism of AOT reverse micelles was studied by infrared spectroscopy. The IR properties of ternary systems formed by Cu(AOT)2/[H20]/CC14 are reported and compared with the corresponding Na(AOT) system. The results show significant differences in interactions of Na + and Cu z+ counterions with H20 molecules and the SO3 headgroup of AOT.

Physicochemical investigations of anionic–nonionic mixed surfactant microemulsions in nonaqueous polar solvents: I. Phase behavior

Colloid and Polymer Science, 2006

Phase behaviors of AOT/ heptane (Hp)/formamide (FA), ethylene glycol (EG), propylene glycol (PG), triethylene glycol (TEG) and glycerol (GLY) have been investigated in the absence and presence of a nonionic surfactant, polyoxyethylene (2) cetyl ether (Brij-52) at 303 K. The phase characteristics of (AOT+ Brij-52)/Hp/(EG or PG or TEG) have been found to be different from that of AOT/Hp/FA systems in respect of both the area of monophasic domain and the appearance of other mesophases. The area of monophasic domain of (AOT+Brij-52)/Hp/EG depends on the content of Brij-52 (X Brij-52) and shows a maximum at X Brij-52 =0.4. A negligible effect on the area of the monophasic domain has been shown by more hydrophobic surfactants, polyoxyethylene(2) stearyl ether (Brij-72) and polyoxyethylene(2) oleyl ether (Brij-92). The effect of oils (dodecane and hexadecane) on the mixed systems stabilized by (AOT+Brij-52) in EG has been investigated. The area of monophasic domain has been found to be dependent on the type of nonaqueous solvents and follows the order GLY>EG>PG>TG. A systematic investigation on the measurement of phase volumes of mixed surfactant systems [AOT+nonionic surfactant(s)] stabilized in oils of different chain lengths (heptane, dodecane and hexadecane) and polar solvent (EG) has been carried out at different compositions of the ingredients to identify the phase transitions of these systems as a function of X Brij-52. The threshold point of phase transition (both W I→W IV and W IV→W II transitions) has been found to be a function of the configuration of added nonionic surfactant, nature of the polar solvent and oil. The conversion of the initial oil/EG droplets into EG/oil droplets with increasing X nonionic has been facilitated for hydrophobic surfactants polyoxyethylene (4) lauryl ether (Brij-30), Brij-52, and Brij-72 in comparison to the hydrophilic surfactants polyoxyethylene(10) cetyl ether (Brij-56) and polyoxyethylene(20) cetyl ether (Brij-58).

Dynamic Light Scattering Study of AOT Microemulsions with Nonaqueous Polar Additives in an Oil Continuous Phase

Langmuir, 1998

Microemulsions with entrapped nonaqueous polar solventssglycerol (Gly), ethylene glycol (EtGy), and formamide (Form)sand an oil (isooctane or n-heptane) continuous phase were studied by dynamic light scattering (DLS). The largest hydrodynamic radii evaluated for the two former systems, by the method of extrapolation to infinite dilution, were respectively 56.5 and 28 Å. The method was not applicable to the latter system (formamide), making the determination of the hydrodynamic radius impossible. It was found that, in these microemulsion systems, the interactions between the droplets are more attractive than the ones observed in water-in-oil microemulsions, being larger in formamide and smaller in glycerol. The droplet structure remains spherical, but evidence of clusters was obtained in all the systems studied. Their formation is attributed to strong attractive interactions.

Micellar Growth and Shape Change in an Oil-in-Water Microemulsion

Langmuir, 1995

Accurate measurements of water, oil, and surfactant self-diffusion coefficients have been made in the microemulsion phase of pentaethylene glycol dodecyl ether (C12E5), water, and decane using nuclear magnetic resonance (NMR) techniques. In conjunction with previously measured 2H NMR relaxation rates, the self-diffusion coefficients are consistent with a limited growth from sphere to prolate (oil-swollen) micelles with an axial ratio 53.5 as a precursor to the bicontinuous structure. @ Kamenka, N.; Kathopoulis, T.; Brun, B.; Nilsson, (6) Lindman, B.; Shinoda, K.; Olsson, U.; Anderson, D.; Karlstrom, (7) Olsson, U.; Wennerstrom, H. Adv.

Effect of 1-alkanols/salt on the cationic surfactant micellar aqueous solutions—A dynamic light scattering study

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011

The effect of 1-alkanols viz., ethanol, 1-butanol and 1-hexanol on five quaternary salts based cationic surfactants in water and in presence of 0.1 M salts has been systematically investigated by viscosity and dynamic light scattering (DLS) technique. The concentration for surfactant varying in non-polar tail, polar head and counterion was kept constant (∼50 mM) throughout. The viscosity data are less detailed, but confirm the general trend of micellar growth and transitions. Influence of 1-butanol on critical micelle concentration (CMC) and degree of counterion dissociation (() was also investigated conductometrically. These measurements were done to supplement the role of counterions in exploring the binding phenomenon due to the effect of salt and alcohol during micellization. The effect of 1-alkanols upon the viscosity and micelle hydrodynamic diameter (D h ) of micelles in the presence of salt at varying concentration and temperature was also examined in detail to explain the hydrophobic interactions and electrostatic effects.