C. Thunig

Experimental results for the L3 phase in a zwitterionic surfactant system and their implications regarding structures

Conditions for existence of the L3 phase have been determined for a system containing water, n-hexanol, and the zwitterionic surfactant n-tetradecyldimethylamineoxide. Electric birefringence, light-scattering, rheology, and electrical-conductivity experiments were performed on this phase. Results are consistent with the existence of platelike micelles, whose diameter changes with surfactant concentration in such a way that it remains comparable to mean plate spacing. This behavior can be understood in terms of a previous L3 phase theory containing randomly oriented plates.

O/W emulsions for cosmetics products stabilized by alkyl phosphates — rheology and storage tests

Abstract Alkyl phosphates are useful as cosmetic emulsifiers. Mono-/diphosphate mixtures derived from long chain Guerbet alcohols combine good emulsification properties with easy handling. Model emulsions containing both emulsifier and a polymeric thickener were characterized by rheological measurements, particle size distributions and stability tests. Emulsion stability was found to be related to the presence of a yield stress. The melting points and Krafft boundaries increase with chain length and can be greatly reduced by chain branching. Solid emulsifiers can form macroscopically homogenous dispersions in water which thicken on heating above the Krafft boundary and re-cooling. These aqueous dispersions may also be used to stabilize emulsions and dispersions.

Electron microscopic and light scattering observation on a system with two iridescent phases

Electron microscopic observations and classical light-scattering measurements have been carried out for dodecyldimethylaminoxide/hexanol/water mixtures in the concentration range where iridescent colors occur. This system has two different iridescent phases. The iridescent phase with more hexanol forms quickly, and the phase with less hexanol forms very slowly. Three different isotropic phases which show strong flow birefringence are found near both iridescent phases. The electron microscopic pictures show clearly that only one of these isotropic phases with strong flow birefringence is a bicontinuous sponge phase (L3h-phase). This is the phase which comes out by adding some alkanol to the upper lamellar phase. The flow birefringent phase below the lower lamellar phase forms unilamellar vesicles. The flow birefringent phase which occurs between both iridescent phases contains multilamellar vesicles and is shown to be a precursor of a lamellar phase.

Phase behavior and dynamic properties in mixed systems of anionic and cationic surfactants: lithium perfluorooctanesulfonate/diethanolheptadecafluoro-2-undecanolmethylammonium chloride (DEFUMAC) and lithium dodecyl sulfate/DEFUMAC aqueous mixtures

Two ternary phase diagrams of the cationic perfluorosurfactant diethanolheptadecafluoro-2-undecanolmethylammonium chloride (DEFUMAC) with an anionic perfluorosurfactant lithium perfluorooctanesulfonate (LiFOS) and an anionic hydrocarbon surfactant lithium dodecyl sulfate (LiDS) have been established at 25°C. The total surfactant concentration was less than 20wt%. In a wide mixing region of the LiFOS/DEFUMAC system, a lamellar-type phase,Pβ, was identified by its texture under a polarization microscope and by its x-ray diffraction pattern. Dispersed fragments ofPβ-phase are present in the dilute solutions in which one surfactant was in excess. The anisotropy of electrical conductivity, flow birefringence, dynamic light scattering, and electric briefringence demonstrate that thePβ fragments are disk-like with a radius of 0.7 μm. The disk-likePβ particles are transformed by shear into a spherical aggregate ofLα above a critical shear gradient. LiDS/DEFUMAC mixed solution forms dispersed and precipitatedLα in the dominant region. Radius and micropolarity of the dispersedLα aggregates are decreased as the ratio of LiDS:DEFUMAC approaches 1:1. On the basis of x-ray diffraction measurement the structure of precipitatedLα-phase seems to consist of monolayers.

Vesicular precipitates from surfactant/cosurfactant mixtures

A new anionic surfactant lauryl amidomethylsulfate (LAMS-) was investigated. The aggregation behaviour was determined by small-angle neutron scattering (SANS) measurements. The Na-salt micelles are highly charged, while the Casalt micelles are almost uncharged. Na-LAMS (100 mM) solutions in the presence of 100 mM CaCl2 undergo several phase transformations with increasing n-hexanol concentration. We found the expected micellar L1 phase and a lamellar phase, but also a novel phase: a white precipitate is formed at the bottom of the sample. With increasing n-hexanol concentration, the precipitate dissolves into a liquid-crystalline Lga phase. Investigation by freeze—fracture transmission electron microscopy, light micros-copy and SANS shows that the precipitate consists of agglomerated polydisperse multilamellar vesicles. The bilayer thickness is about 20 A and is independent of the composition, whereas the interlamellar distance is strikingly linked to the concentrations of cosurfactant (sur-factant/cosurfactant ratio) and electrolyte. With increasing cosurfactant content, the bilayers become less rigid and resulting thermal undulations force the membranes apart until a common Lga phase is formed. This transition is an example of a bonding—nonbonding transition of membranes.

LAMELLAR-INVERSE HEXAGONAL TRANSITION OF 4-(1-BUTYLOCTYL)BENZENESULPHONATE IN ELECTROLYTE/WATER/OCTANOL SOLVENTS: A FRACTAL APPROACH TO THE HOMOGENEOUS NUCLEATION OF THE LIQUID CRYSTALLINE PHASE FROM THE SOLUTION

The behavior of mesophases in the sodium 4-(1-butyloctyl)benzenesulphonate/Mg(NO3)2/water system was determined by using crossed polars, polarized light microscopy, and small-angle X-ray diffraction. In comparison with the binary system without Mg(NO3)2, these systems showed changes in the formation of phases. A considerable shift of the two-phase region (isotropic/lamellar) towards a lower concentration of surfactant has been found. In water/n-octanol mixtures the lamellar phase was formed bellow 10% of cosurfactant (n-octanol). Above 30% of a cosurfactant, the transition of lamellar-inverse hexagonal phase has been observed due to the corresponding convex/concave change of the bilayer curvature. The formation of the inverse hexagonal phase was caused by an increase in the cosurfactant concentration. By heating the sample above 55°C the solution became isotropic; following cooling the homogeneous nucleation of an inverse hexagonal phase from the isotropic solution was observed. The fractal approach was applied to characterize the dendrite-like growth of the inverse hexagonal phase using the “box-counting” method. The fractal dimensions for the diffusion-limited aggregation resulting in the growth of the starlike, as well as the rod–like, dendrites were found to be Dstar∼1.36–1.4 (time dependent) and Drod=1.25 (time independent), respectively.

Gel-like rheological behavior of mesophases in photoreactive azodye/water/KCl systems

Publisher Summary Chapter describes dyes, which are useful as dyestuffs, paints, and coloring materials on various industrial applications. Especially, azo-dyes are photoreactive compounds which induce photochromic cis-trans isomerization. Amphiphiles including azo-dye as a rigid spacer form bilayers in aqueous dispersions and supramolecular assemblies in aqueous methanol solutions. The amphiphilic azo-dye in aqueous methanol solutions forms rodlike swarms at low amphiphilic azo-dye concentrations and liquid crystals at high amphiphilic azo-dye concentrations. This chapter illustrates a phase diagram for ternary systems of azo-dye Levafix Goldgelb E-G (F9)/water/KCl. The ternary systems of dilute F9 concentrations display three isotropic (Li, sb, and L3mBl) phases, an anisotropic (L α) phase, and an inhomogeneous (L α+ qlc) phase. The chapter also describes the investigation of the rheological behavior by oscillatory measurements and shear stress–strain examinations. In addition of viscoelastic behavior, apparent yield stress is observed for L3mBl and L α phases. While the rheological behavior is independent of KCl concentration, it strongly depends on the F9 concentration. The storage modulus, loss modulus, and apparent yield stress are scaled against F9 concentration over L3mBl and L α phases, indicating the existence of gel-like structure.