Physicochemical characterization of PEG1500-12-acyloxy-stearate micelles and liquid crystalline phases

PEG 12-acyloxy-stearates are used as drug delivery carriers that have low cell damage effects. The mechanical and physical properties surrounding these processes and surfactants are still however not known. In this study, the physicochemical micellar properties of PEG 12-acyloxy-stearates were characterized by optical microscopic, nuclear magnetic resonance, and small-angle X-ray scattering techniques. We determined the phase diagrams of the surfactants as a function of surfactant concentration and temperature, the micellar size and shape, and micellar dynamics. We found that each surfactant has a micellar, cubic Im3m, and hexagonal phase. The aggregation number in the discrete cubic phase, as determined by small-angle X-ray scattering, was approximately 150 for each surfactant, and showed no measurable chain-length dependence. The diffusion coefficients of the surfactant showed a discontinuity between the micellar and cubic phases, where the cubic phases gave very low values on the order of 10(-)(16) m(2) s(-)(1): this value indicates a non-bicontinuous cubic structure. In summary, these surfactants behave to a large extent as nonionic poly(ethylene glycol) surfactants with extended PEG headgroups.     

Polymerisation of liquid crystalline phases in binary surfactant/water systems

The polymerisation of a polymerisable fatty acid surfactant (sodium 10-undecenoate) has been studied in both its self-assembled and non self-assembled forms. Polymerisation in non self-assembled solution was achieved to near completion. The polymerisation produces a surface active polymer. The self-assembling behaviour of this pre-polymerised form differs markedly from that observed for the monomeric surfactant [1]. A lamellar phase only is formed in the polymeric phase diagram with no hexagonal or lamellar gel phases being observed. Polymerisation in the different self-assembled forms of sodium 10-undecenoate reached a limit of approximately 30% only, i.e., the surfactant aggregates act to inhibit the polymerisation. The nature of the hydrocarbon chain was found to play a critical role in determining the effect that polymerisation had on the underlying geometry of the surfactant molecules. When the chains are in a fluid-like state (as for the micellar and hexagonal phases) the original monomeric matrix remains largely unchanged. Whereas partial polymerisation of the lamellar gel phase results in a phase transformation.In addition the hydrolysis of the fatty acid soap at low concentrations (close to the critical micelle concentration) has been investigated. Hydrolysis was shown to produce both the parent fatty acid and an acid soap dimer. The presence of these species greatly affects the solution behaviour in this region of the phase diagram shifting the critical micelle concentration to very high concentrations of sodium 10-undecenoate (ca. 0.4 M).     

Elongated silica nanoparticles with a mesh phase mesopore structure by fluorosurfactant templating

Mesoporous silica materials with pore structures such as 2D hexagonal close packed, bicontinuous cubic, lamellar, sponge, wormhole-like, and rectangular have been made by using surfactant templating sol-gel processes. However, there are still some "intermediate" phases, in particular mesh phases, that are formed by surfactants but which have not been made into analogous silica pore structures. Here, we describe the one-step synthesis of mesoporous silica with a mesh phase pore structure. The cationic fluorinated surfactant 1,1,2,2-tetrahydroperfluorodecylpyridinium chloride (HFDePC) is used as the template. Like many fluorinated surfactants, HFDePC forms intermediate phases in water (including a mesh phase) over a wider range of compositions than do hydrocarbon surfactants. The materials produced by this technique are novel elongated particles in which the layers of the mesh phase are oriented orthogonal to the main axis of the particles.     

Phase polymorphism by mixing of poly(oxyethylene)-poly(dimethylsiloxane) copolymer and nonionic surfactant in water

The phase behavior of the water/poly(oxyethylene)-poly(dimethylsiloxane) copolymer (Si25C3EO51.6)/pentaoxyethylene dodecyl ether (C12EO5) ternary system has been studied. Both the silicone copolymer and the surfactant have equal volumes of hydrophilic and lipophilic parts; i.e., these are balanced amphiphiles. Although only a lamellar phase is observed in water-Si25C3EO51.6 and water-C12EO5 binary systems, a variety of liquid crystalline phases, including normal micellar cubic (I1), hexagonal (H1), bicontinuous cubic (V1), lamellar (L(alpha)), reverse bicontinuous cubic (V2), and reverse hexagonal (H2), are observed in the copolymer-rich region of the ternary phase diagram. The small C12EO5 molecules dissolve at the hydrophobic interface in the thick bilayer of the Si25C3EO51.6 L(alpha) phase occupying a large area of the total interface of the aggregates and modulate the curvature of the aggregates. Hence a variety of self-assembled structures are observed. In contrast, Si25C3EO51.6 is not dissolved in the thin bilayer of the C12EO5 lamellar phase (L'(alpha)). Hence, the C12EO5 L'(alpha) phase coexists with copolymer-rich L(alpha) and H2 phases. Consequently, small surfactant molecules are dissolved in a large silicone copolymer aggregate to induce a change in layer curvature, but a large copolymer molecule is hard to incorporate with surfactant aggregates.     

Memory effects across surfactant mesophases

We report a detailed analysis of deuteron NMR spectra of micellar, lamellar, cubic, and hexagonal mesophases in the aqueous non-ionic surfactant system C(12)E(6)/water. Samples are prepared with and without shear. Particular attention is paid to an interesting temperature-driven phase sequence that includes all of the above phases that are studied before and after shear parallel or perpendicular to the magnetic field direction. Surprising memory effects are found across mesophase transitions. These memory effects provide clues to the structure of the various phases.     

Synthesis and lyotropic phase behavior of novel nonionic surfactants for the crystallization of integral membrane proteins

A series of new sugar-based nonionic surfactants have been synthesized and their lyotropic liquid crystalline properties characterized. When in contact with water, these surfactants formed a range of lyotropic liquid crystalline phases, including cubic, hexagonal, and lamellar, as well as a separate micellar phase. These are features that have promise for the crystallization of integral membrane proteins.     

Amphiphilic N-benzoyl-1-amino-1-deoxy-D-glucitol derivatives forming thermotropic lamellar, columnar and different types of cubic mesophases

Novel amphiphilic glucamine derivatives have been synthesized. These are N-benzoyl-1-deoxy1-methylamino-D-glucitols and N-benzoyl-1-amino-1-deoxy-D-glucitols carrying one, two or three aliphatic chains (CnH2n 1O- with n 3, 6 and 12) grafted to the benzamido group. The thermotropic mesophases of these compounds were studied by thermal polarizing optical microscopy and differential scanning calorimetry, and some also by X-ray scattering. Depending on the number and the length of the alkyl chains lamellar, bicontinuous cubic, hexagonal columnar or inverted micellar cubic mesophases were detected by analogy with lyotropic systems. In the contact region between lamellar phases of the single chain amphiphiles and micellar cubic phases of the mesomorphic triple chain compounds, hexagonal columnar phases can be induced. A hexagonal columnar phase was also induced in the contact region between a bicontinuous and a micellar cubic mesophase. The lyotropic liquid crystalline behaviour of the dodecyloxy substituted N-benzoyl-1-deoxy-1-methylamino-D-glucitols was investigated by the solvent penetration method using ethylene glycol as protic solvent. On increasing the solvent content, the double chain compound forms a cubic and a lamellar mesophase and the triple chain compound forms a hexagonal columnar lyomesophase. The dodecyloxy substituted compounds were also investigated with respect to their behaviour as thin films at the air-water interface using a Langmuir film-balance. Different types of pi/Aisotherms were observed whereby the molecular areas at collapse were determined either by the size of the carbohydrate head group (single chain compounds) or by the number of alkyl chains (double and triple chain compound).     

Influence of glycerol on the formation of lyotropic mesophases —microscopic texture observations for determining preliminary phase diagrams of binary K-soap/glycerol systems

Analogously to aqueous K-soap/water systems already examined, the glycerol-containing systems KC _n /G (KC _n ;n=12, 14, 16, 18, 22; G=glycerol) are also able to build up hexagonal, lamellar, optically isotropic, gel-like and crystalline phases. These preliminary phases have been identified by texture observations of contact samples and singular concentrations with a polarizing microscope. The appertaining phase regions have been plotted in the binary phase diagrams.Correspondences and differences between these systems have been elucidared by drawing a comparison. Mosaic texture and oily streaks are typical of the lamellar phase. Spherulites are mainly found in the heterogeneous two-phase region lamellar/isotropic. The textures of the hexagonal phase are of fan-like morphology. The appearance of the gel phase texture resembles globular or curd-like structures.The influences exerted by the increasing chain lengths of the K-soaps (KC _n ,n=12–22) on the phase regions in the binary systems (KC _n /G) can be described as follows. The concentrations required for forming the hexagonal and the lamellar phase respectively are shifted toward lower K-soap concentrations. The concentration range in which the hexagonal phase is stable is diminished. The temperature range in which the hexagonal phase is stable becomes larger. The upper temperature limit of the lamellar phase region is lowered.Binary aqueous and glycerol-containing K-soap systems have the following common features: The hexagonal phase is built up at low soap concentrations. The lamellar phase is formed at high soap concentrations. The lamellar phase is formed at high soap concentrations. An optically isotropic region is inserved between the lamellar and the hexagonal phase in aqueous and glycerol-containing systems of the types KC₁₄, KC₁₆ and KC₁₈. The temperature of the transition hexagonalisotropic phase (HS) runs through a maximum value. On increasing the chain length the formation of the hexagonal phase is shifted in the direction of lower soap concentrations.Aqueous and glycerol-containing K-soap mixtures differ in the following essential points: The lyotropic mesophases (H, L, I) of aqueous systems are formed at considerably lower soap concentrations than the corresponding phases of glycerol-containing systems. The lamellar phases of aqueous systems reach the regions of very low soap concentrations. The lyotropic mesophases of aqueous systems are built up at temperatures lower than the corresponding ones of glycerol-containing mixtures. In aqueous systems the concentration range of the lamellar phase increases with increasing chain length, in contrast to glycerol-containing systems where it is diminished.     

X-ray diffraction study of the structure of carboxymethylcellulose-cationic surfactant complexes.

We have investigated dilute aqueous solutions of an anionic polymer (carboxymethylcellulose) mixed with cationic surfactants of different chain lengths (dodecyl to octadecyl trimethylammonium bromides: DTAB, TTAB, CTAB and OTAB). The structures of the concentrated phases formed above the precipitation threshold were studied by X-ray diffraction. Different body-centred cubic structures with space groups Pm3n were observed in the presence of surfactant with a short aliphatic chain (DTAB), despite the fact that the polymer persistence length is comparable to the repeat distance of the structure (5 nm). For larger surfactant chain lengths (TTAB and CTAB), the structure of the precipitates can be either cubic (Pm3n) or 2D hexagonal depending on the initial surfactant and polymer concentrations. For still larger chain length (OTAB), the structure becomes lamellar. This structural evolution from micellar cubic towards 2D hexagonal and lamellar is attributed to the decrease of the local curvature of the surfactant aggregates, as observed for flexible synthetic polymers and short DNA fragments under similar conditions. Furthermore, the structure of the bulk complexes formed just below the precipitation threshold anticipates the structure seen in the precipitated phases.     

Pulsed gradient NMR study of anisotropic surfactant diffusion in the caesium perfluoro octanoate/D2O system

We use pulsed field gradient ¹⁹F NMR to measure the diffusion coefficients of surfactant molecules in the isotropic and lamellar phases of the caesium perfluoro octanoate (CsPFO)/D₂O system. An aligned lamellar sample is created by cooling through the nematic phase in the presence of a 1·4 T magnetic field. The director in the lamellar phase does not respond to ordinary field strengths, thus the aligned sample can be rotated clockwise or counterclockwise to place the director at a magic angle, where measurement of diffusion coefficients becomes possible. From a pair of so-obtained coefficients, we derive the principal values of the diffusion tensor corresponding to the directions parallel and perpendicular to the director (D_⊥ and D_⊥). We found D_∥ to be at least 20 times D_∥ a much larger anisotropy than is seen in electrical conductivity and water diffusion in similar systems. These results are compared to electrical conductivity, water and dye diffusion measurements.     

Lyotropic and interfacial behaviour of an anionic gemini surfactant

The sodium salt of N,N'-hexane-bis (1-dodecen-1-ylsuccinamic acid) is an anionic dimeric (gemini) surfactant. A flooding penetration scan of this surfactant in water demonstrates a sequence of lyotropic phases at room temperature (20 degrees C). Preparation of surfactant-water mixtures has resulted in a phase diagram which shows that the same sequence of phases exists up to 100 degrees C. These phases are tentatively assigned to the sequence: micellar to normal hexagonal (H1) to cubic (V1) to lamellar (Lalpha). The interfacial tension at the n-heptane/water interface has been determined in the presence of this surfactant. The surfactant head group area at the interface is large (2.8+/-0.3 nm2 at 298 K) and the interfacial tension above the critical micelle concentration is low (7 mN m(-1)), but considerably higher than the ultra-low values that have been reported for cationic dimeric surfactants at various hydrocarbon-water interfaces.     

Preliminary Communications. Micellar phases formed by a solution of l-serine hydrochloride decylester and orthophosphoric acid

Polarizing microscope studies showed that the isotropic solution composed of l-serine hydrochloride decylester and orthophosphoric acid forms micellar cholesteric, nematic and lamellar phases, whereas the solution of the optically inactive ester gives micellar nematic and lamellar phases. The phase transitions were tentatively assigned as the result of two concurrent reactions at which ortho-phosphoserine hydrochloride decylester and orthophosphoric acid monodecylester are produced. Dilution of the optically active and the optically inactive lamellar phases with water gave a cholesteric and a nematic phase, respectively. The nematic director is aligned perpendicular to the glass plate, whereas that of the cholesteric phase is aligned parallel.     

Thermotropic and lyotropic phase behaviour of monoalkyl glycosides

We have studied the thermotropic and lyotropic phase behaviour of seven monoalkyl glycosides using polarizing microscopy, differential scanning calorimetry and X-ray diffraction. The phase behaviour of these non-ionic surfactants is compared with that of two previously studied monoalkyl glycosides \[1]. We have found that small modifications in chemical structure can lead to large changes in the phase behaviour. The results reveal the effect of changes in alkyl glycoside chemical structure on the phase behaviour, in particular, on the melting point, the clearing point, the solubility in water, and the extent of the lamellar and curved phases. Seven out of the nine surfactants were found to exhibit thermotropic mesomorphism. Furthermore, in the presence of water, three formed lamellar (L ), type I cubic (Q ) and type I hexagonal (H ) phases, two formed lamellar and cubic phases, and two I I formed only lamellar phases. The cubic phase in each case was indexed, either from powderlike or monodomain samples, as spacegroup I a3 d . The lowest order low angle X-ray spacings were found to lie on single, continuous lines with varying water content across the L , Q and H phases, implying epitaxial relationships between these phases at the phase boundaries. I a a I     

Hydration of dimethyldodecylamine-N-oxide: enthalpy and entropy driven processes

Dimethyldodecylamine-N-oxide (DDAO) has only one polar atom that is able to interact with water. Still, this surfactant shows very hydrophilic properties: in mixtures with water, it forms normal liquid crystalline phases and micelles. Moreover, there is data in the literature indicating that the hydration of this surfactant is driven by enthalpy while other studies show that hydration of surfactants and lipids typically is driven by entropy. Sorption calorimetry allows resolving enthalpic and entropic contributions to the free energy of hydration at constant temperature and thus directly determines the driving forces of hydration. The results of the present sorption calorimetric study show that the hydration of liquid crystalline phases of DDAO is driven by entropy, except for the hydration of the liquid crystalline lamellar phase which is co-driven by enthalpy. The exothermic heat effect of the hydration of the lamellar phase arises from formation of strong hydrogen bonds between DDAO and water. Another issue is the driving forces of the phase transitions caused by the hydration. The sorption calorimetric results show that the transitions from the lamellar to cubic and from the cubic to the hexagonal phase are driven by enthalpy. Transitions from solid phases to the liquid crystalline lamellar phase are entropically driven, while the formation of the monohydrate from the dry surfactant is driven by enthalpy. The driving forces of the transition from the hexagonal phase to the isotropic solution are close to zero. These sorption calorimetric results are in good agreement with the analysis of the binary phase diagram based on the van der Waals differential equation. The phase diagram of the DDAO-water system determined using DSC and sorption calorimetry is presented.     

Pressure effects on lipidic direct phases: the dodecyl trimethyl ammonium chloride-water system

The direct lyotropic polymorphism of dodecyltrimethylammonium chloride (DTAC) was investigated by synchrotron X-ray diffraction at different water concentrations under compression up to 2 kbar, i.e., in the pressure intermediate range where interesting biophysical transformations occur and the functional characteristics of cell membranes are altered. The results show that pressure induces the transition from the hexagonal phase to the micellar Pm3n cubic phase in hydrated samples (c between 0.5 and 0.6, c being the weight concentration of lipid in the mixture) and the transition from the bicontinuous Ia3d cubic phase to the hexagonal phase in drier samples (c = 0.8). By increasing the pressure on very dry samples, a lamellar L(alpha) phase was observed to form transitorily at the Ia3d cubic-hexagonal phase transition. Phase compressibility and then the lipid and water partial molecular compressibilities were derived as a function of pressure and concentration. As a result, we assessed the very low compressibility of the hydration water within the lipid phases, and we demonstrated that the compressibility of DTAC is very dependent on pressure. Moreover, the molecular parameters of DTAC calculated in the different phases during compression confirmed that pressure induces small but continuous conformational changes, definitely different from the large changes observed in lipid molecules forming type II structures.     

Cubic phase prepared in an anionic/amphoteric surfactant/oleic acid/decane/water system and the relationship with the neighboring phase

The formation, properties, and structure of discontinuous cubic phase in the pseudo-ternary system consisting of N'-carboxyethyl N'-hydroxyethyl N-aminoethyl dodecylamide (imidazoriniumbetain), sodium and triethanol amine salt of polyoxyethylene (1.5 mol) myristyl ether sulfate, oleic acid, decane, and water at a constant surfactant/water ratio of 4/6 were studied by means of small-angle X-ray scattering, freeze-fracture transmission electron microscopy, static light scattering, and dynamic rheology to gain an insight in its origin and interrelation with neighboring phases. It was found that the cubic phase occupied a rather wide region in a constructed ternary phase diagram, including from 25 to 45% of decane. Its properties and structural parameters varied with changing the oil content. The decane addition caused the swelling of spherical micellar aggregates. This resulted in an increase of their diameter up to 35 nm, which was ca. nine times larger than that of the initial micelles, and micellar volume fraction (packing fraction) up to 72 vol. %, which was close to the theoretically possible value of 74 vol. % for the close-packed spherical particles. The cubic phase was surrounded by a micellar L1 phase from the water-rich side (separated by a short two-phase region), two-phase region (cubic + oil) from the oil-rich side, and a lamellar phase from the surfactant-rich side. A transition from the L1 phase to the cubic state at the packing fraction of 60 vol. % was caused by an increase in the packing density of micellar aggregates, occurring with the decane addition. When it reached 72 vol. %, the oil started forming a separated phase owing to the inability of micelles to dissolve it. The important observation is that the adjacent phase from the surfactant-rich side was a lamellar one made up of flat bilayers. The preliminary data showed that the lamellar phase coexisted with cylindrical micelles in the intermediate two-phase region separating the cubic and lamellar phases.     

Phase behavior of polyion-surfactant ion complex salts: effects of surfactant chain length and polyion length

The aqueous phase behavior of a series of complex salts, containing cationic surfactants with polymeric counterions, has been investigated by visual inspection and small-angle X-ray scattering (SAXS). The salts were alkyltrimethylammonium polyacrylates, CxTAPAy, based on all combinations of five surfactant chain lengths (C6, C8, C10, C12, and C16) and two lengths of the polyacrylate chain (30 and 6 000 repeating units). At low water contents, all complex salts except C6TAPA6000 formed hexagonal and/or cubic Pm3n phases, with the hexagonal phase being favored by lower water contents. The aggregate dimensions in the liquid crystalline phases changed with the surfactant chain length. The determined micellar aggregation numbers of the cubic phases indicated that the micelles were only slightly aspherical. At high water contents, the C6TAPAy salts were miscible with water, whereas the other complex salts featured wide miscibility gaps with a concentrated phase in equilibrium with a (sometimes very) dilute aqueous solution. Thus, the attraction between oppositely charged surfactant aggregates and polyions decreases with decreasing surfactant chain length, and with decreasing polyion length, resulting in an increased miscibility with water. The complex salt with the longest surfactant chains and polyions gave the widest miscibility gap, with a concentrated hexagonal phase in equilibrium with almost pure water. A decrease in the attraction led to cubic-micellar and micellar-micellar coexistence in the miscibility gap and to an increasing concentration of the complex salt in the dilute phase. For each polyion length, the mixtures for the various surfactant chain lengths were found to conform to a global phase diagram, where the surfactant chain length played the role of an interaction parameter.     

Use of the ternary phase diagram of a mixed cationic/glucopyranoside surfactant system to predict mesostructured silica synthesis

Mixed surfactant systems have the potential to impart controlled combinations of functionality and pore structure to mesoporous metal oxides. Here, we combine a functional glucopyranoside surfactant with a cationic surfactant that readily forms liquid crystalline mesophases. The phase diagram for the ternary system CTAB/H(2)O/n-octyl-beta-D-glucopyranoside (C(8)G(1)) at 50 degrees C is measured using polarized optical microscopy. At this temperature, the binary C(8)G(1)/H(2)O system forms disordered micellar solutions up to 72 wt% C(8)G(1), and there is no hexagonal phase. With the addition of CTAB, we identify a large area of hexagonal phase, as well as cubic, lamellar and solid surfactant phases. The ternary phase diagram is used to predict the synthesis of thick mesoporous silica films via a direct liquid crystal templating technique. By changing the relative concentration of mixed surfactants as well as inorganic precursor species, surfactant/silica mesostructured thick films can be synthesized with variable glucopyranoside content, and with 2D hexagonal, cubic and lamellar structures. The domains over which different mesophases are prepared correspond well with those of the ternary phase diagram if the hydrophilic inorganic species is assumed to act as an equivalent volume of water.     

Ribbon phases in surfactant systems Comparisons between experimental results and predictions of a theoretical model

Ribbon phases consist of long cylindrical aggregates that have non-circular normal sections. We have recently pointed out that scattering data for a large number of different intermediate ribbon phases of lower than hexagonal symmetry found in ionic surfactant systems indicate that these phases have a structure possessing a centred rectangular symmetry. In this communication, we have investigated the aggregate dimensions for the phases with cylindrical aggregates, i.e., the hexagonal phases and the centred rectangular ribbon phases. Previously published phase diagrams, small angle X-ray and neutron scattering data and ²HNMR data for these phases in different systems have been used for this purpose. The results are that the axial ratios of the aggregates increase when the temperature decreases, when the surfactant concentration increases, and when the average surfactant charge decreases. Models that semi-quantitatively describe the thermodynamics of the micellar, hexagonal and lamellar phases, which are based on the Poisson-Boltzmann cell model approach, have previously been presented in the literature. We have extended these models to treat also the ribbon phases. The results from the calculations show the same trends with respect to changes in the dimensions of the non-circular aggregates upon changes in temperature, surfactant concentration and average surfactant charge, as those obtained experimentally. Theoretically calculated phase diagrams with ribbon phases are also presented. Based on the predictions of the model and some previously published experimental data for hexagonal phases, it is proposed that the formation of non-circular, cylindrical aggregates is a general property of single-chain, ionic surfactant/water systems, and that these aggregates in general pack on hexagonal lattices. The normal sections of these aggregates are circular on average, on account of the fact that the degree of deformation and the orientation of deformation changes along the axis of the aggregates and with time. Only for some systems, temperatures and surfactant concentrations do the asymmetric aggregates line up and ribbon phases with centred rectangular symmetry are obtained. The driving mechanisms for the transition from the hexagonal phase with asymmetric (fluctuating) cylinders and further to the centred rectangular phase with asymmetric (stiff) cylinders is also discussed. It is argued that this phase transition is of the first order.     

NMR self-diffusion measurements in inverse micellar cubic phases

Abstract

We have measured self-diffusion coefficients of amphiphile and water molecules in novel inverse micellar lyotropic cubic phases using the pulsed field gradient NMR technique. We investigated two different ternary lyotropic systems: oleic acid/sodium oleate/water, and dioleoylglycerol/dioleoylphosphatidylcholine/water. Both of these systems have previously been shown by one of us to form a cubic phase of space group Fd3m, whose structure is a complex packing of two types of disconnected quasi-spherical inverse micelles embedded in a 3D hydrocarbon matrix. The amphiphile translational diffusion coefficients determined for the first time by ¹H NMR in both systems are surprisingly large. Thus the self diffusion coefficients of amphiphiles may not provide a reliable way of distinguising inverse micellar from inverse bicontinuous phases. The water self-diffusion coefficient has been determined to have a value of 2·4 × 10^?12 m² s^?1, a value which is more than two orders of magnitude lower than that typically observed for inverse bicontinuous cubic phases. This confirms unambiguously the inverse micellar topology of the Fd3m cubic phase, and indicates that the value of the water diffusion coefficient should permit inverse micellar and inverse bicontinuous structures to be reliably distinguished, even for systems where the structure has not been previously determined by diffraction.