Bulk and dispersed aqueous phase behavior of phytantriol: effect of vitamin E acetate and F127 polymer on liquid crystal nanostructure

Phytantriol (3,7,11,15-tetramethylhexadecane-1,2,3-triol, PHYT) is a cosmetic ingredient that exhibits similar lyotropic phase behavior to monoolein (GMO), forming bicontinuous cubic liquid crystalline structures (Q(II)) at low temperatures and reversed hexagonal phase (H(II)) at higher temperatures in excess water. Despite these similarities, phytantriol has received little attention in the scientific community. In this study, the thermal phase behavior of the binary PHYT-water and ternary PHYT-vitamin E acetate (VitEA)-water systems have been studied and compared with the behavior of the dispersed cubosomes and hexosomes formed with the aid of a stabilizer (Pluronic F127). The phase behavior and nanostructure were studied using crossed polarized light microscopy (CPLM), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) techniques. The presence of lipophilic VitEA in the PHYT-water system suppressed the temperature of the Q(II)-to-H(II)-to-L2 transitions, indicating that lipophilic compounds, in relatively small amounts, may have a significant impact on the phase behavior. Increasing the F127 concentration in the phytantriol-based cubosome system did not induce the Q(II)(Pn3m) to Q(II)(Im3m) transition known for the GMO-water system. This indicates a different mode of interaction between F127 and the lipid domains of phytantriol-water systems. Taken together, these results indicate that phytantriol may not only provide an alternative lipid for preparation of liquid crystalline systems in excess water but may also provide access to properties not available when using GMO.     

Polymerisation in lyotropic liquid-crystalline phases of dioctadecyldimethylammonium bromide

The polymerisation of styrene in lyotropic liquid-crystalline (LC) phases of dioctadecyldimethylammonium bromide (DODAB) in water is explored. Amphiphile concentrations between 20 and 50 wt % are employed. The study is set out as a model study for polymerisation reactions in nonstabilised, nonfunctional bilayer systems. X-ray characterisation was used to assess the phase behaviour of the lyotropic mesophases before, during and after polymerisation. The DODAB/water system forms the lamellar phase within the concentration range considered. Addition of styrene to the lamellar phase of DODAB at an equimolar ratio induces a phase shift to a bicontinuous cubic phase at elevated temperatures near the phase-transition temperature. Upon polymerisation within this cubic phase, the phase structure is maintained if the system is kept at constant temperature; however, if the polymer/amphiphile phase is cooled, the lamellar phase, being typical of the DODAB/water system, is restored. It is concluded that, as a result of phase separation between the polymer and the amphiphile phase, the polymerisation in lyotropic LC phases does not provide a stable copy of the templating amphiphile phase. This is in analogy to the observations for polymerisations in other lyotropic phases. Received: 16 March 2000 Accepted: 1 July 2000     

Formation of amphiphile self-assembly phases in protic ionic liquids

A range of protic ionic liquids (PILs) have been identified as being capable of supporting the self-assembly of the nonionic surfactants myverol 18-99 K (predominantly monoolein) and phytantriol. PIL-surfactant penetration scans have provided a high throughput technique to determine which lyotropic liquid crystalline phases were formed in the 40 PIL-surfactant systems investigated. Lamellar, inverse hexagonal, and bicontinuous cubic phases that are stable in excess PIL have been observed in surfactant-PIL systems. The studied PILs possess a wide range of solvent properties, including surface tension and viscosity. The nature of the formed amphiphile self-assembly phases is discussed in terms of the PIL structure and solvent properties.     

Nanostructural studies on monoelaidin-water systems at low temperatures

In recent years, lipid based nanostructures have increasingly been used as model membranes to study various complex biological processes. For better understanding of such phenomena, it is essential to gain as much information as possible for model lipid structures under physiological conditions. In this paper, we focus on one of such lipids--monoelaidin (ME)--for its polymorphic nanostructures under varying conditions of temperature and water content. In the recent contribution (Soft Matter, 2010, 6, 3191), we have reported the phase diagram of ME above 30 °C and compared with the phase behavior of other lipids including monoolein (MO), monovaccenin (MV), and monolinolein (ML). Remarkable phase behavior of ME, stabilizing three bicontinuous cubic phases, motivates its study at low temperatures. Current studies concentrate on the low-temperature (<30 °C) behavior of ME and subsequent reconstruction of its phase diagram over the entire temperature-water composition space (temperature, 0-76 °C; and water content, 0-70%). The polymorphs found for the monoelaidin-water system include three bicontinuous cubic phases, i.e., Ia3d, Pn3m, and Im3m, and lamellar phases which exhibit two crystalline (L(c1) and L(c0)), two gel (L(β) and L(β*)), and a fluid lamellar (L(α)) states. The fluid isotropic phase (L(2)) was observed only for lower hydrations (<20%), whereas hexagonal phase (H(2)) was not found under studied conditions. Nanostructural parameters of these phases as a function of temperature and water content are presented together with some molecular level calculations. This study might be crucial for perception of the lyotropic phase behavior as well as for designing nanostructural assemblies for potential applications.     

Amphotropic liquid-crystalline behaviour of glycolipids in amino acid ionic liquids

We examined lyotropic liquid-crystalline behaviour of glycolipids (GLs) with a normal alkyl chain or a diacetylene-functionalised alkyl chain in several amino acid ionic liquids (AAILs). It was found that the mixtures of GL and AAIL form various nanosegregated liquid-crystalline phases, such as smectic, bicontinuous cubic and hexagonal columnar phases, depending on the two-component ratio and AAIL species. The observed liquid-crystalline behaviours were summarised as phase diagrams. It is noteworthy that the employment of amino acid anions with superior hydrogen-bonding ability, such as aspartic and glutamic acid anions, gives a phase diagram with a wide liquid-crystalline region. Comparing with a phase diagram obtained for the GL/water mixtures, we gained insights on the similarity/dissimilarity between water and AAILs as self-organisation media of amphiphiles. For the diacetylene-functionalised molecule, UV irradiation was carried out to progress polymerisation. It is of interest that the polymerisation reaction progressed when the glycolipid formed a smectic phase in an AAIL while a reaction progress was not found when it formed a bicontinuous cubic phase in another AAIL. We believe that AAILs have a great potential to be a liquid media not only for amphiphiles but for various functional materials, such as polymers and colloids, to form novel assemblies.     

Shear rheology of lyotropic liquid crystals: a case study

We have investigated the rheological properties of lyotropic liquid crystals (LCs) formed by self-assembled neutral lipids and water, their relationship with the topology of the structure, and their dependence on temperature and water content. The phase diagram of a representative monoglyceride-water system, determined by combining cross-polarized optical microscopy and small-angle X-ray scattering (SAXS), included four structures: lamellar, hexagonal, gyroid bicontinuous cubic (Ia3d), and double diamond bicontinuous cubic (Pn3m), as well as several regions of two-phase coexistence of some of the above structures. Rheology in the linear viscoelastic regime revealed a specific signature that was characteristic of the topology of each structure considered. The order-order transitions lamellar-to-cubic and cubic-to-hexagonal, as well as the order-disorder transitions from each LC to an isotropic fluid, were easily identified by following the development of the storage and loss moduli, G' and G', respectively. The viscoelastic properties of both bicontinuous cubic phases were shown to be strongly frequency-dependent, following a pseudo-Maxwell behavior, with multiple relaxation times. Cubic-to-cubic transitions were nicely captured by scaling the longest relaxation time, tau, with either temperature or water volume fraction. Therefore, the set of the three main parameters used to establish the rheological behavior of the structure, that is, G', G', and relaxation time, tau, constitutes a consistent ensemble to identify the structures of the liquid crystal. Finally, relaxation spectra, extracted for all liquid crystalline phases, allowed an additional possible identification criterion of the various structures considered.     

Cross-linked normal hexagonal and bicontinuous cubic assemblies via polymerizable gemini amphiphiles

The synthesis and lyotropic liquid-crystalline (LLC) phase behavior of a homologous series of intrinsically cross-linkable gemini surfactants are described. These novel bis(alkyl-1,3-diene)-based phosphonium gemini amphiphiles exhibit "normal" hexagonal (H(I)), Type I bicontinuous cubic (Q(I)), and lamellar (L(alpha)) phases in water, and can be photocross-linked with retention of phase architecture in each case. On the basis of their locations on the phase diagram, their powder X-ray diffraction profiles, and the physical properties of the cross-linked materials, the Q(I) phases formed by these gemini monomers are consistent with four possible bicontinuous cubic architectures with P or I space group symmetry that have been identified previously for small molecule amphiphiles. The extent of polymerization (i.e., the degree of diene conversion) achieved in the LLC phases was determined to be in the 23% to 71% range using UV-vis spectrometry, which is more than sufficient to extensively stabilize the systems. The resulting cross-linked H(I), L(alpha), and Q(I) phases are stable up to 300 degrees C in air. To our knowledge, these reactive amphiphiles constitute the first example of a polymerizable gemini surfactant, and the first example of a cross-linkable amphiphile system that can be polymerized in both the H(I) and a Q(I) mesophase with retention of phase microstructure.     

High-throughput discovery of novel steric stabilizers for cubic lyotropic liquid crystal nanoparticle dispersions

High-throughput methodologies have been employed to establish structure-property relationships and assess the effectiveness of nonionic steric stabilizers for inverse bicontinuous cubic lyotropic liquid crystalline nanoparticulate dispersions of monoolein and phytantriol. The ability of the stabilizers to disperse the lipids was compared with that of the commonly employed triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer Pluronic F127, which was used as a positive control. The poly(ethylene oxide) stearate class of stabilizers (commercially known as Myrj) were discovered to be effective as steric stabilizers for cubosomes, while retaining the internal nanostructure of the "parent" bulk phase. In particular, Myrj 59, with an average of 100 poly(ethylene oxide) units, was more effective than F127 at dispersing phytantriol, forming stable phytantriol cubosome dispersions at a concentration of 0.1 wt %, 5-fold lower than that achievable with Pluronic F127. The discovery of this new effective class of stabilizers for cubosomes, specifically enabled by high-throughput approaches, broadens the versatility of components from which to construct these interesting potential drug delivery and medical imaging nanoparticles.     

pH-responsive lyotropic liquid crystals for controlled drug delivery

We present a food-grade lyotropic liquid crystal system, capable of responding to pH variations with a reversible switch in both the structure and physical properties. The system, which is composed by monolinolein and linoleic acid (97:3 wt % ratio) in the presence of excess water at 37 °C and 150 mM ionic strength, is specifically designed to reversibly change from a Im3m reverse bicontinuous cubic phase to a H(II) reverse columnar hexagonal phase, when changing the pH from neutral (pH 7) to acidic (pH 2) conditions, to simulate intestine and stomach conditions, respectively. The pH responsiveness is provided by the linoleic acid, which, being a weak acid (pK(a) ≈ 5), is essentially in the deprotonated charged state at pH 7 and mainly protonated and neutral at pH 2, imposing changes in the critical packing parameter (CPP) of the lyotropic liquid crystal. The use of this system as an efficient controlled-release delivery vehicle is demonstrated on the model hydrophilic drug phloroglucinol, by both release and diffusion studies at different pH, as followed by ultraviolet-visible (UV-vis) spectroscopy. The Im3m cubic phase at pH 7 is shown to release 4 times faster than the H(II) phase at pH 2, making this system an ideal candidate for oral administration of drugs for targeted delivery in intestine or colon tracts.     

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.     

"Sponge" nanoparticle dispersions in aqueous mixtures of diglycerol monooleate, glycerol dioleate, and polysorbate 80

Lipid nanoparticles of nonlamellar lyotropic phases have a wide solubilizing and encapsulating spectrum for a range of substances thanks to their nanostructured interior featuring both lipophilic and hydrophilic domains. As a consequence, these systems have emerged as promising drug delivery systems in various pharmaceutical and diagnostic applications. Here we present the phase behavior and dispersion properties of a novel three-component lipid system composed of diglycerol monooleate (DGMO), glycerol dioleate (GDO), and polysorbate 80 (P80) which shows several advantageous features relating to drug delivery applications including: spontaneous dispersion formation with a narrow size distribution and tunable particle phase-structure. The obtained phase diagram shows the presence of lamellar (L(alpha)), hexagonal (H(2)), and reverse bicontinuous cubic (V(2)) liquid crystalline phases and an inverse micellar (L(2)) solution. A particularly interesting observation is the presence of a phase region where two liquid phases coexist, most likely the L(2) and L(3) ("sponge phase"). These two phase structures appear also to coexist in the submicron particles formed in the dilute water region, where the L(3) element appears to stabilize nanoparticles with inner L(2) structure. Increasing the fraction of the dispersing P80 component results in the growth of the more water rich L(3) "surface phase" at the expense of the size of the inner L(2) core.     

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.     

A Comprehensive Study on Lyotropic Liquid–Crystalline Behavior of an Amphiphile in 20 Kinds of Amino Acid Ionic Liquids

We examined the self‐organization behavior of a designed amphiphilic molecule in 20 kinds of amino acid ionic liquids composed of 1‐butyl‐3‐methylimidazolium cation and natural amino acid anion ([C4mim][AA]). Addition of [C4mim][AA], regardless of their anion species, to the amphiphile provided homogeneous mixtures showing lyotropic liquid–crystalline (LC) behavior. Upon increasing the component ratio of [C4mim][AA] in the mixtures, a successive change of the mesophase patterns from inverted hexagonal columnar, in some case via bicontinuous cubic, to layered phases was observed. By examining the LC properties at various temperatures and component ratios, we constructed lyotropic LC phase diagrams. Interestingly, the appearance of these phase diagrams is greatly different according to the selection of [AA]. Through comparison, we found that the self‐organization behavior of an amphiphile in ionic liquids can be tuned by controlling their ability to form hydrogen‐bond, van der Waals, and π‐π interactions.     

Calculations of and evidence for chain packing stress in inverse lyotropic bicontinuous cubic phases

Inverse bicontinuous cubic lyotropic phases are a complex solution to the dilemma faced by all self-assembled water-amphiphile systems: how to satisfy the incompatible requirements for uniform interfacial curvature and uniform molecular packing. The solution reached in this case is for the water-amphiphile interfaces to deform hyperbolically onto triply periodic minimal surfaces. We have previously suggested that although the molecular packing in these structures is rather uniform the relative phase behavior of the gyroid, double diamond, and primitive inverse bicontinuous cubic phases can be understood in terms of subtle differences in packing frustration. In this work, we have calculated the packing frustration for these cubics under the constraint that their interfaces have constant mean curvature. We find that the relative packing stress does indeed differ between phases. The gyroid cubic has the least packing stress, and at low water volume fraction, the primitive cubic has the greatest packing stress. However, at very high water volume fraction, the double diamond cubic becomes the structure with the greatest packing stress. We have tested the model in two ways. For a system with a double diamond cubic phase in excess water, the addition of a hydrophobe may release packing frustration and preferentially stabilize the primitive cubic, since this has previously been shown to have lower curvature elastic energy. We have confirmed this prediction by adding the long chain alkane tricosane to 1-monoolein in excess water. The model also predicts that if one were able to hydrate the double diamond cubic to high water volume fractions, one should destabilize the phase with respect to the primitive cubic. We have found that such highly swollen metastable bicontinuous cubic phases can be formed within onion vesicles. Data from monoelaidin in excess water display a well-defined transition, with the primitive cubic appearing above a water volume fraction of 0.75. Both of these results lend support to the proposition that differences in the packing frustration between inverse bicontinuous cubic phases play a pivotal role in their relative phase stability.     

Lyotropic liquid-crystalline phases formed by Pluronic P123 in ethylammonium nitrate

Aggregation of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer, Pluronic P123, is promoted in a room temperature ionic liquid, ethylammonium nitrate (EAN). A series of lyotropic mesophases including normal micellar cubic (I1), normal hexagonal (H1), lamellar (Lalpha), and reverse bicontinuous cubic (V2) are identified at 25 degrees C by using polarized optical microscopy and small-angle X-ray scattering techniques. Such self-assembly behavior of P123 in EAN is similar to those observed in H2O or 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMim(+)][PF6(-)]) systems except for the presence of the V2 phase in EAN and the absence of the I 1 phase in [BMim(+)][PF6(-)]. This suggests that the ionic solvent of EAN plays similar roles as H2O and [BMim(+)][PF6(-)] during the aggregation process and solvates the PEO blocks through hydrogen-bond interaction. Furthermore, the hydrogen bonds are considered to form between the ethylammonium cations and oxygen atoms of the PEO blocks as confirmed by Fourier transform infrared spectra of P123-EAN assemblies. This deduction is also consistent with the results from differential scanning calorimetry and thermogravimetric analysis. The additional V2 phase appearing in the P123-EAN system is attributed to the higher affinity for the relatively hydrophobic PPO blocks to EAN than to water, which might reduce the effective area of the solvophilic headgroup and increase the volume of the solvophobic part. The obtained results may help us to better understand the self-assembly process for amphiphilic block copolymers in protic solvents.     

Self-consistent field theory for lipid-based liquid crystals: hydrogen bonding effect

A model to describe the self-assembly properties of aqueous blends of nonionic lipids is developed in the framework of self-consistent field theory (SCFT). Thermally reversible hydrogen bonding between lipid heads and water turns out to be a key factor in describing the lyotropic and thermotropic phase behavior of such systems. Our model includes reversible hydrogen bonding imposed in the context of the grand canonical ensemble and exact conditions of binding equilibrium. The lipid molecules are modeled as a rigid head and a flexible Gaussian tail, and the water molecules are treated explicitly. Here, we focus on systems where the lipid molecule has a relatively small hydrophilic head compared to the hydrophobic tail, such as monoolein in water. Experimentally, this system has both normal phase sequences (inverted hexagonal to inverted double gyroid cubic phase) and reverse phase sequences (lamellar to inverted double gyroid cubic phase) as the water volume fraction increases. From SCFT simulations of the model, two phase diagrams corresponding to temperature independent or dependent interaction parameters chi are constructed, which qualitatively capture the phase behavior of the monoolein-water mixture. The lattice parameters of the simulated mesophases are compared with the experimental values and are found to be in semiquantitative agreement. The role of various structural and solution parameters on the phase diagrams is also discussed.     

Chelating DTPA amphiphiles: ion-tunable self-assembly structures and gadolinium complexes

A series of chelating amphiphiles and their gadolinium (Gd(iii)) metal complexes have been synthesized and studied with respect to their neat and lyotropic liquid crystalline phase behavior. These amphiphiles have the ability to form ion-tunable self-assembly nanostructures and their associated Gd(III) complexes have potential as magnetic resonance imaging (MRI) contrast enhancement agents. The amphiphiles are composed of diethylenetriaminepentaacetic acid (DTPA) chelates conjugated to one or two oleyl chain(s) (DTPA-MO and DTPA-BO), or isoprenoid-type chain(s) of phytanyl (DTPA-MP and DTPA-BP). The thermal phase behavior of the neat amphiphiles was examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and cross polarizing optical microscopy (POM). Self-assembly of neat amphiphiles and their associated Gd complexes, as well as their lyotropic phase behavior in water and sodium acetate solutions of different ionic strengths, were examined by POM and small and wide angle X-ray scattering (SWAXS). All neat amphiphiles exhibited lamellar structures. The non-complexed amphiphiles showed a variety of lyotropic phases depending on the number and nature of the hydrophobic chain in addition to the ionic state of the hydration. Upon hydration with increased Na-acetate concentration and the subtle changes in the effective headgroup size, the interfacial curvature of the amphiphile increased, altering the lyotropic liquid crystalline structures towards higher order mesophases such as the gyroid (Ia3d) bicontinuous cubic phase. The chelation of Gd with the DTPA amphiphiles resulted in lamellar crystalline structures for all the neat amphiphiles. Upon hydration with water, the Gd-complexed mono-conjugates formed micellar or vesicular self-assemblies, whilst the bis-conjugates transformed only partially into lyotropic liquid crystalline mesophases.     

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.     

Phase behavior of lipid-based lyotropic liquid crystals in presence of colloidal nanoparticles

We have investigated the microstructure and phase behavior of monoglyceride-based lyotropic liquid crystals in the presence of hydrophilic silica colloidal particles of size comparable to or slightly exceeding the repeat units of the different liquid crystalline phases. Using small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC), we compare the structural properties of the neat mesophases with those of the systems containing silica colloidal particles. It is found that the colloidal particles always macrophase separate in inverse bicontinuous cubic phases of gyroid (Ia3d) and double diamond (Pn3m) symmetries. SAXS data for the inverse columnar hexagonal phase (H(II)) and lamellar phase (L(α)) suggest that a low volume fraction of the nanoparticles can be accommodated within the mesophases, but that at concentrations above a given threshold, the particles do macrophase separate also in these systems. The behavior is interpreted in terms of the enthalpic and entropic interactions of the nanoparticles with the lamellar and hexagonal phases, and we propose that, in the low concentration limit, the nanoparticles are acting as point defects within the mesophases and, upon further increase in concentration, initiate nucleation of nanoparticles clusters, leading to a macroscopic phase separation.     

Time-resolved in situ studies of the formation of cubic mesoporous silica formed with triblock copolymers

The mechanism of formation of two different cubic mesoporous silica materials formed with Pluronic triblock copolymers is investigated with in situ time-resolved small-angle synchrotron X-ray scattering, in situ time-resolved 1H nuclear magnetic resonance, and time-resolved transmission electron microscopy. The materials studied are the micellar cubic (Imm) SBA-16 formed with Pluronic F108 and the bicontinuous cubic (Iad) silica material formed with Pluronic P103 and NaI. The formation mechanisms of the two cubic structures are shown to be dissimilar. For the Imm material, in the early stages of the synthesis, flocs of unordered micelles are observed, but areas where the micelles have started to order are also present. With time, there is an increase in order; however, there is a coexistence of unordered micelles and ordered material all through this study. The bicontinuous cubic silica is formed via a different path. The system is phase-separated already before the addition of the silica source, which implies that a concentrated phase is present, acting as the structure director of the Iad structure. The results are compared with earlier reports on the formation of the hexagonal SBA-15 material.