Isotropic Micellar Phase Research Articles

Removal of Pollutants by Ferrihydrite Nanoparticles Combined with Brij L4 Self-Assembled Nanostructures

Release of contaminants such as pharmaceuticals, dyes, pesticides, and industrial wastes due to anthropogenic activities is a threat to human health and the environment. Self-assembled nanostructures of nonionic surfactants are highly efficient in removing organic and inorganic pollutants from various environmental media. Here, we present an evaluation of the pollutant-removal efficiency of Brij L4 nonionic surfactant as a function of the surfactant concentration and self-assembled structures. In addition, small-angle X-ray scattering (SAXS) and rheology were employed to investigate interactions between the Brij L4 isotropic micellar phase and lyotropic liquid crystals and ferrihydrite nanoparticles (Fh NPs). Ferrihydrite nanoparticles in the micellar phase destabilized lyotropic liquid crystals at low surfactant concentrations, while remaining stable in lyotropic phases at high concentrations. Maximum pollutant-removal efficiency (22%) was obtained using a self-assembled nanostructure of pure Brij L4 at 1 wt %. However, Fh NPs are nanoporous and strongly interact with negatively charged organic matter, enhancing the pollutant-removal efficiency of 10 wt % Brij L4. We constructed binary and pseudo-binary phase diagrams at 25 °C of the surfactant in water and in the presence of ferrihydrite nanoparticles, respectively. The Brij L4/water binary phase diagram identified rod-shaped structures at 10 wt % of surfactant. The results of this study identify effective strategies for formulating highly efficient pollutant-removal systems using nanotechnology.

Phase behavior of soybean phosphatidylcholine and glycerol dioleate in hydrated and dehydrated states studied by small-angle X-ray scattering.

Soybean phosphatidylcholine (SPC) and glycerol dioleate (GDO) form liquid crystal nanostructures in aqueous environments, and their mixtures can effectively encapsulate active pharmaceutical ingredients (API). When used in a subcutaneous environment, the liquid crystalline matrix gradually hydrates and degrades in the tissue whilst slowly releasing the API. Hydration dependent SPC/GDO phase behavior is complex, non-trivial, and still not fully understood. A deeper understanding of this system is important for controlling its function in drug delivery applications. The phase behavior of the mixture of SPC/GDO/water was studied as a function of hydration and lipid ratio. Small-angle X-ray scattering (SAXS) was used to identify space groups in liquid crystalline phases and to get detailed structural information on the isotropic reverse micellar phase. The reported pseudo ternary phase diagram includes eight different phases and numerous multiphase regions in a thermodynamically consistent way. For mixtures with SPC as the predominant component, the system presents a reverse hexagonal, lamellar and R3m phase. For mixtures with lower SPC concentrations, reverse cubic (Fd3m and Pm3n) as well as intermediate and isotropic micellar phases were identified. By modeling the SAXS data using a core-shell approach, the properties of the isotropic micellar phase were studied in detail as a function of concentration. Moreover, SAXS analysis of other phases revealed new structural features in relation to lipid-water interactions. The new improved ternary phase diagram offers valuable insight into the complex phase behavior of the SPC/GDO system. The detailed structural information is important for understanding what APIs can be incorporated in the liquid crystal structure.

Stereochemical Purity Can Induce a New Crystalline Mesophase in Phytantriol Lipids.

The impact of stereochemical purity of lipids on their self-assembly behavior is critical for establishing their true phase behavior from their commercial counterparts, which often contains stereoisomeric mixtures and other impurities. Here, stereochemically pure phytantriol (PT), (3,7,11,15-tetramethylhexadecane-1,2,3-triol) was synthesized from the natural trans-phytol and its thermotropic and lyotropic phase behavior in water investigated by small-angle X-ray scattering (SAXS), polarized optical microscopy (POM), and differential scanning calorimetry (DSC). These chemically pure lipids contain two chiral centers at the hydrophilic head group region and two chiral centers at the lipophilic tail region, allowing us to address the question of whether the molecular stereochemistry is related to the macroscopic phase behavior of phytantriol. In contrast to its commercial stereoisomeric mixtures, which form an isotropic micellar phase, neat (2S,3S,7R,11R)-3,7,11,15-tetramethylhexadecane-1,2,3-triol (S,S-PT) shows a smectic lamellar phase at room temperature, whereas (2R,3R,7R,11R)-3,7,11,15-tetramethylhexadecane-1,2,3-triol (R,R-PT) forms solid crystals. The lyotropic phase behavior of R,R-PT appears to be identical to that of the previously reported commercial stereoisomeric PT mixtures. In contrast, S,S-PT exhibits a different phase behavior. A lamellar crystalline phase (Lc) is formed instead of an isotropic micellar phase at a low water content, which also coexisted with other phases at low temperature. Subtle change in the shape of the diastereomers leads to variable steric interactions and subsequently affects the packing of the lipids at the molecular level, thereby influencing its self-assembling behavior. Finally, lipidic cubic phase crystallization of the membrane protein bacteriorhodopsin yielded a larger number of microcrystals with a higher average crystal length from S,S-PT than from commercial PT, suggesting faster nucleation.

Molecular Dynamics in the Lyophases of Copolymer P123 Investigated with FFC NMR Relaxometry.

Associative block copolymers of the type (EO) x(PO) y(EO) x (where EO and PO represent ethylene and propylene oxides, respectively) in aqueous solution have far reaching commercial applications such as solubilization, controlled-drug delivery, etc. The molecular dynamics of a self-associating triblock copolymer (EO)20(PO)70(EO)20 (known as P123 with a molecular weight of ∼5800), in aqueous solution (D2O), consisting of various lyotropic liquid crystalline phases such as isotropic micellar, cubic, hexagonal, and lamellar phases, is investigated using the fast field cycling nuclear magnetic resonance (FFC NMR) relaxometry technique in the Larmor frequency range from 5 kHz to 30 MHz. A nuclear spin-relaxation model consisting of chain modes (Rouse modes) and order fluctuation (OF) modes typical for polymers and liquid crystals, respectively, is considered to explain the observed proton magnetic relaxation dispersion (PMRD) data in the lyophases under investigation. The PMRD analysis in both isotropic micellar and cubic phases revealed a Rouse frequency dependence of spin-lattice relaxation rate ( R1), i.e., R1 ∝ -τs ln(ωτs), in the entire frequency range of study. Hexagonal and lamellar phase data show Rouse modes as well as OF modes, leaving the signature of the latter as R1 ∝ ω- p, where p ∼ 0.5 is typical for nematic mesogens. The activation energies were also determined from segmental correlation times in the lyophases of study. To the best of our knowledge, the present FFC NMR relaxometry study is unique and quantitative in unraveling molecular dynamics of the associative copolymer P123 in aqueous solution.

Investigation of Phase States, Thermo-Morphologic, Magneto-Morphologic and Refractive Properties of Mesophases in Dodecyltrimethyl Ammonium Bromide – Water Lyotropic Liquid Crystalline System

Abstract We report the phase states in dodecyltrimethyl ammonium bromide/water (DDTMABr–H2O) lyotropic liquid crystalline system. The temperature-concentration phase diagram of this system has been determined. Isotropic micellar L1 phase, nematic-calamitic NC and hexagonal E mesophases have been observed in DDTMABr/H2O system. Dynamics of transformations of magnetically induced textures in NC and E mesophases has been investigated. Temperature and concentration dependences of the refractive index in the L1 phase, NC and E mesophases have been determined. The appearance of the magnetically induced aligned textures of NC mesophase and changes of the optical birefringence vs. time have been investigated.

Self-assembly of triton X-100 in water solutions: a multiscale simulation study linking mesoscale to atomistic models.

A multiscale scheme is proposed and validated for Triton X-100 (TX-100), which is a detergent widely employed in biology. The hybrid particle field formulation of the model allows simulations of large-scale systems. The coarse-grained (CG) model, accurately validated in a wide range of concentrations, shows a critical micelle concentration, shape transition in isotropic micellar phase, and appearance of hexagonal ordered phase in the experimental ranges reported in the literature. The fine resolution of the proposed CG model allows one to obtain, by a suitable reverse mapping procedure, atomistic models of micellar assemblies and of the hexagonal phase. In particular, atomistic models of the micelles give structures in good agreement with experimental pair distance distribution functions and hydrodynamic measurements. The picture emerging by detailed analysis of simulated systems is quite complex. Polydisperse mixtures of spherical-, oblate-, and prolate-shaped aggregates have been found. The shape and the micelle behavior are mainly dictated by the aggregation number (Nagg). Micelles with low Nagg values (∼40) are spherical, while those with high Nagg values (∼140 or larger) are characterized by prolate ellipsoidal shapes. For intermediate Nagg values (∼70), fluxional micelles alternating between oblate and prolate shapes are found. The proposed model opens the way to investigations of several mechanisms involving TX-100 assembly in protein and membrane biophysics.

Comparative investigations of the thermotropic and optical refractive properties in micellar isotropic phase and nematic-calamitic mesophase of hexadecyltrimethyl ammonium bromide/water and hexadecyltrimethyl ammonium bromide/water/1-decanol lyotropic liquid crystalline systems

We report the thermotropic properties and measurements of the temperature and concentration dependences of the refractive index in isotropic micellar L 1 phase and nematic-calamitic N C mesophase of the hexadecyltrimethyl ammonium bromide/water (CTAB/H2O) and hexadecyltrimethyl ammonium bromide/water/1-decanol (CTAB/H2O/DeOH) lyotropic liquid crystalline systems. The effect of amphiphile and aliphatic alcohol concentrations on the refractive properties of L 1 phase and N C mesophase has been studied. Jump-like changes of the refractive properties in regions of the L 1 phase–N C mesophase lyotropic and thermotropic phase transitions have been found. The sufficient effect of CTAB addition on the refractive index value has been found for the CTAB/H2O and CTAB/H2O/DeOH lyotropic systems. In this work, the shape of micelles in L 1 phase and N C mesophase has been also estimated. Estimation showed that structural units of L 1 phase are the isometric spherical micelles, and structural units of N C mesophase are the anisometric rod-like micelles. Typical textures of N C mesophase in the CTAB/H2O and CTAB/H2O/DeOH lyotropic systems and the heterophase regions of the N C mesophase–isotropic liquid thermotropic phase transitions are presented.

Phenomenological study of ferrofluid to ferrosmectic phase transition in lyotropic liquid crystals

We present a mean-field analysis for the properties of phases and phase transitions in ferrosmectic in lyotropic liquid crystals. The model free energy is written in terms of the orientational order parameter, translational order parameter, magnetization and micellar concentration. The phase transition from isotropic micellar ferrofluid to lyotropic ferrosmectic is of first order while the phase transitions from the lyotropic ferronematic to lyotropic ferrosmectic phase and lyotropic parasmectic to lyotropic ferrosmectic phase can be either first or second order depending on the concrete substance. The temperature and concentration dependence of the magnetic birefringence and Cotton–Mouton constant are calculated in the isotropic micellar ferrofluid phase.

Isotropic micellar to tilted lamellar phase transition in lyotropic liquid crystals

We extend our previous phenomenological model for the isotropic micellar to lamellar (smectic-A) phase transition to the isotropic micellar to tilted lamellar (smectic-C) (I–Lt) phase transition in lyotropic liquid crystals. We analyze the influence of micellar concentration on the I–Lt phase transition. The conditions for the I–Lt phase transition and the stability conditions of the tilted lamellar phase are calculated. The temperature dependence of the non-linear dielectric effect in the isotropic micellar phase above the I–Lt phase transition is calculated. Within this model the I–Lt phase transition is found to be always first order.

Thermodynamically controllable transition from 3D to 2D self-assembly of a hydrogelator induced by the phase behavior of triblock copolymers

Triblock copolymer PE6200 (PEO10.5–PPO30–PEO10.5) in aqueous solution can undergo a transition from an isotropic micellar phase to an anisotropic lamellar phase at a specific temperature. Based on this feature, the self-assembly behavior of a benzenetetracarboxylic acid based hydrogelator in aqueous solutions of PE6200 has been investigated. The results of small angle X-ray scattering (SAXS) measurements indicated that the hydrogelator self-assembled into stable three-dimensional network structures below 50°C. In the range of 50–60°C, a transition from three-dimensional to two-dimensional self-assembly was observed, which can be attributed to the fact that PE6200 undergoes a transition from an isotropic micellar phase to an anisotropic lamellar phase. Differential scanning calorimetry (DSC) and varying temperature laser Raman spectroscopy further confirmed the thermodynamically controllable transition of 3D to 2D self-assembly. Controlling the self-assembly by utilizing the phase behavior of triblock copolymers is a novel strategy.

Thermotropic and lyotropic liquid crystalline phases of Guerbet branched-chain -D-glucosides

The effect of chain branching on glycolipid thermotropic and lyotropic phases was investigated for a series of synthetic β-D-glucosides derived from Guerbet alcohols, whose total hydrocarbon chain length ranged from C8 to C24. The compounds, which can be viewed as isosteric mimics for glycoglycerolipids, were synthesised in high purity and their liquid crystalline phases were studied using optical polarising microscopy (OPM), and small-angle X-ray diffraction. When dry, the shortest compound (total C8) exhibits a monotropic Lα phase while longer ones (C16 and C20) adopt inverse hexagonal HII phases. The C24 compound forms an ordered lamellar phase at room temperature, but exhibits a metastable HII phase upon cooling. Curiously the intermediate chain length homologue (C12) adopts an isotropic inverse micellar (L2) phase in the dry state over the range of temperatures studied. Upon hydration, the C8 compound dissolves, and the C12 compound forms a fluid lamellar Lα phase. The C16 Guerbet glucoside (i.e. β-Glc-C10C6) exhibits an inverse bicontinuous cubic phase of space group Ia3d in excess water, never previously observed in branched-chain lipids, and very seldom observed in excess water. The C20 compound remains in the HII phase upon hydrating, with the lattice parameter swelling substantially.

Food Volatile Compounds Facilitating HII Mesophase Formation: Solubilization and Stability

Four lipophilic food volatile molecules of different chemical characteristics, phenylacetaldehyde, 2,6-dimethyl-5-heptenal, linalool, and trans-4-decenal, were solubilized into binary mixtures of monoolein/water, facilitating the formation of reverse hexagonal (H(II)) mesophases at room temperature without the need of solvents or triglycerides. Some of the flavor compounds are important building blocks of the hexagonal mesostructure, preventing phase transition with aging. The solubilization loads were relatively high: 12.6, 10.0, 12.6, and 10.0 wt % for phenylacetaldehyde, 2,6-dimethyl-5-heptenal, linalool, and trans-4-decenal, respectively. Phenylacetaldehyde formed mixtures of lamellar and cubic phases. Linalool, 2,6-dimethyl-5-heptenal, and trans-4-decenal induced structural shift from lamellar directly to H(II) mesophase, remaining stable at room temperature. Lattice parameters were found to increase with water content and to decrease with temperature and/or food volatile content. trans-4-Decenal produces more stable H(II) mesophase compared to linalool-loaded mesophase. At 40-60 °C, depending on the chemical structure and on the solubilization location of the food volatile compounds, the H(II) mesophase transforms to isotropic micellar phase, facilitating the release of the food volatile compounds. Molecular interactions suggest the existence of two consecutive stages in the solubilization process.

Molecular dynamics simulation for phase behavior of amphiphilic solution

The phase behavior of amphiphilic solution is investigated by molecular dynamics simulation of amphiphilic rigid dimers with explicit solvent molecules. Our simulations show that three kinds of phases (isotropic micellar, hexagonal and lamellar phases) are formed at a lower temperature by quenching from a random configuration of amphiphilic molecules in solution at a higher temperature. It is ascertained that an isotropic micellar phase changes into a hexagonal phase, and then into a lamellar phase as the amphiphilic concentration increases. It is also found that the global orientational order parameter can be used to distinguish these three kinds of phases. From the detailed analyses of the phase behavior, it is concluded that the hydrophilic repulsion plays an important role in the formation of the hexagonal phase while the hydrophobic attraction plays a crucial role in the formation of the lamellar phase.

Phase Transition in Salt-Free Catanionic Surfactant Mixtures Induced by Temperature

Aggregate transitions in salt-free catanionic surfactant mixtures of tetradecyltrimethylammonium hydroxide (TTAOH)/fatty acid were investigated as a function of surfactant concentration and temperature. Lauric acid (LA), myristic acid (MA), and palmitic acid (PA) were chosen for the current study. The TTAOH/LA mixture exhibited rich phase behavior at room temperature. With increasing total surfactant concentration (c(T)), a bluish vesicular (L(alphav)) phase, an isotropic micellar (L(1)) phase, and a birefringent lamellar (L(alpha)) phase were observed. Between the L(alphav) phase and the L(1) phase, a narrow L(alpha)'/L(1) two-phase region was determined. With increasing temperature, a transition from the L(alpha) phase to the L(1) phase was induced at higher c(T) whereas at lower c(T) an opposite transition from the L(1) phase to the L(alphav) phase was noticed. Thus surprisingly, we observed bilayer-to-micelle and micelle-to-bilayer transitions in the same catanionic surfactant system, both induced by the temperature increase. Replacing LA by MA and PA caused a continuous increase in the average Krafft point of the mixture. The L(alphav)-phase region and phase-separated region become larger. Moreover, a single L(1)-phase region was absent within the investigated temperature range.

Phase diagram and physicochemical properties of the n-octyl α-d-glucoside/water system

Four experimental methods were used to study the phase diagram, as well as the thermodynamic and structural properties of the binary system n-octyl α-D-glucoside/water in the temperature range 25–130 °C. Sorption calorimetry allows one to determine the activity of water and enthalpy of mixing as functions of water content at constant temperature, while DSC scans temperature at constant composition and provides information on enthalpies of phase transitions. Therefore, the combination of the two calorimetric methods is a powerful tool to study composition–temperature phase diagrams. While calorimetry can be used to determine boundaries of the phases, NMR and SAXS methods are used to study their structures. A detailed phase diagram of the system is presented. A liquid crystalline cubic phase previously not reported in the system was found. The hydration in the system is endothermic, excluding the exothermic formation of hydrates. Using the sorption calorimetric method the lengths of the very short tie lines between the isotropic micellar and liquid crystalline phases were determined. Van der Waals’s differential equation was used to calculate the slopes of the phase boundaries. The parameters of the lamellar, cubic and hexagonal liquid crystalline phases were determined by means of SAXS. It was found that the area per surfactant headgroup in the liquid crystalline phases varied with composition.

Micelle Shape Transformation in the Isotropic Phase of the Ammonium Perfluorooctanoate/Heavy Water Binary Mixture

The size and shape of the aggregates in the homogeneous isotropic micellar phase of the binary system ammonium perfluorooctanoate/heavy water (APFO/D2O) have been extensively investigated by small- and wide-angle X-ray scattering, optical polarizing microscopy, self-diffusion NMR, and electrical conductivity techniques, as a function of temperature and surfactant concentration. The experimental results strongly suggest that there is a change in the structure of the micellar aggregates where the micelles undergo a shape transition, changing from spherocylinder (rod-shaped), at low surfactant concentration (WA 28 wt % APFO).

Study of 1,2-Octanediol as Cosurfactant of Sodium Dodecyl Sulfate

The phase diagram of the sodium docecyl sulfate (SDS)/1,2-octanediol/water system at 25.0 ± 0.1 °C is given in this paper. The system shows an isotropic normal micellar phase at high water concentration, and two liquid crystalline phases characterized as the hexagonal phase and the lamellar phase. The diol behaves as a short-chain alkanol, except that the extended lamellar phase is stabilized at a very low SDS content. The lamellar phase is also formed by 1,2-octanediol with water. The rheology technique was applied to characterize the phases. The lamellar phase can be divided into four different zones according to the flow behavior. Some of the samples close to the boundary show structural transitions induced by shearing. Both liquid crystalline phases are very elastic, but they show very different relaxation times. The surfactant concentration affects size, stiffness, and the dynamic properties of the cylindrical units in the hexagonal phase.

Phase Behavior and Polymerization Kinetics of a Semifluorinated Lyotropic Liquid Crystal

Recently, amphiphilic monomers that are capable of forming lyotropic liquid crystalline phases have been utilized in a variety of applications including emulsion polymerization, development of nanocomposites, and the formation of polymeric surfactants. A new class of fluorinated amphiphilic monomers that exhibit lyotropic mesophases has shown great promise in ophthalmic applications. Initial studies indicate that the monomer possesses a lamellar morphology at certain concentrations that when polymerized would yield a material with anisotropic properties ideal for repairing retinal tears. Characterization of the polymerization kinetics of these fluorinated monomers provides a better understanding of conditions such that structure retention can be obtained. The fluorinated amphiphiles exhibit varying phase morphology ranging from an isotropic micellar phase to discontinuous cubic and lamellar liquid crystalline phases with increasing concentration and variation in the percent neutralization of the acid moiety. The lyotropic liquid crystalline order changes significantly with respect to percent neutralization. The polymerization kinetics follow a trend of decreasing order with increasing neutralization in that the fastest rates are seen in samples with higher degrees of order specifically in the lamellar liquid crystalline phase. The polymerization rate decreases to a minimum in samples of cubic morphology with low degrees of overall order. The higher polymerization rates in the lamellar phase are due to a decrease in the termination rate. Additionally, the polymerization behavior and morphology have a tremendous impact on the resulting polymer.

Influence of the chain length of K-soaps on the phase diagram and structural parameters of nonaqueous liquid crystals and the gel phase in K-soap/glycerol binary systems

Analogously to the aqueous K-soap/water systems already examined, the five glycerol · (Gl)-containing systems KCn/Gl (n = 12, 14, 16, 18, 22) also built up hexagonal (Hα), lamellar (Lα), isotropic micellar (S), gel-like (G) and crystalline phases (C). These phases were identified by texture observations with a polarizing microscope, by differential scanning calorimetry measurements and by X-ray diffraction investigations. The appertaining phase regions were plotted in the binary phase diagram. Binary Gl-containing K-soap systems have the following properties. The Hα phase is built up at low soap concentration. The Lα phase is formed at high soap concentrations. The temperature of the phase transition Hα ⇆ S runs through a maximum. Increasing the chain lengths of the soaps shifts the formation of the Hα phase to lower soap concentration. A strong correlation between the chain length of K-soaps and the d values of Lα, Hα, G and C phases is found. Based on the comparison of the X-ray diffractograms of the G phase a structural model is proposed. The G phase consists of two groups of domains with two different dimensions.

Cubic phases of amphiphilic molecular aggregates

Stability and geometry of the lyotropic periodic cubic mesophases are considered in the framework of a general symmetry based phenomenological approach. A limited number of cubic structural types is shown to be formed by amphiphilic molecular aggregates due to the specific nature of self-organizing units. The related thermodynamic models predict topology of phase diagrams and specific features of transitions between isotropic, lamellar, cubic bicontinuous and cubic micellar phases.