Isotropic Micellar Solution Research Articles

Molecular-thermodynamic approach to predict micellization, phase behavior and phase separation of micellar solutions. I. Application to nonionic surfactants

We present a detailed description of a molecular-thermodynamic approach which consists of blending a molecular model of micellization with a thermodynamic theory of phase behavior and phase separation of isotropic (surfactant–water) micellar solutions. The molecular model incorporates the effects of solvent properties and surfactant molecular architecture on physical factors which control micelle formation and growth. These factors include (i) hydrophobic interactions between surfactant hydrocarbon chains and water, (ii) conformational effects associated with hydrocarbon-chain packing in the micellar core, (iii) curvature-dependent interfacial effects at the micellar core–water interface, and (iv) steric and electrostatic interactions between surfactant hydrophilic moieties. The free energy of micellization gmic is computed for various micellar shapes Sh and micellar-core minor radii lc. The ‘‘optimum’’ equilibrium values, l*c, Sh*, and g*mic, are obtained by minimizing gmic with respect to lc and Sh. The deduced ‘‘optimum’’ micellar shape Sh* determines whether the micelles exhibit two-dimensional, one-dimensional, or no growth. These results are then utilized in the thermodynamic theory to predict a broad spectrum of micellar solution equilibrium properties as a function of surfactant concentration and temperature. These properties include (1) the critical micellar concentration, (2) the micellar size distribution, (3) the critical surfactant concentration for the onset of phase separation, and (4) other thermodynamic properties such as the osmotic compressibility. The proposed molecular-thermodynamic approach provides an excellent description of a wide range of experimental findings in aqueous solutions of nonionic surfactants belonging to the polyoxyethylene glycol monoether and glucoside families.

Self-association of an α,ω-type (bolaform) surfactant: Phase diagram, self—diffusion, and NMR studies of eicosane-1,20-bis(triethylammonium bromide)

The binary phase diagram (temperature vs composition) of the cationic bolaform (α,ω-type) surfactant eicosane-1,20-bis (triethylammonium bromide) has been determined by polarizing microscopy and water deuteron NMR methods. The surfactant is easily soluble in water giving an extended isotropic solution phase followed by a normal hexagonal liquid crystalline phase (E) at higher surfactant concentrations. On increasing the temperature the liquid crystalline phase extends to the surfactant-rich side. The 2H NMR quadrupolar splitting values in the E phase are found to increase at first with increasing surfactant concentration, then to decrease and go through zero splitting; then the splitting values increase again sharply with increasing surfactant concentration. The micellar phase has a very low capacity to solubilize hydrophobic substances. The narrow 1H and 14N NMR bandwidths as well as the NMR self-diffusion data for water and surfactant indicate the formation of small, closely spherical miceless in the entire isotropic micellar solution phase.

Measurements of density and expansion coefficient for the nematic, lamellar smectic, and isotropic phase of micellar systems

Measurements of the density and expansion coefficient as a function of temperature are presented for two micellar systems, namely, decylammonium chloride/NH4Cl/water, and cesium perfluorooctanoate/water. The measurements cover the lamellar smectic, the nematic, and the isotropic micellar solution. The measurements show that away from the phase transitions, the density decreases smoothly with increasing temperature. At the nematic-to-isotropic transition the density shows steplike features, indicating a change in the micellar structure at the transition, with denser packing of the amphiphiles in the micelles of the isotropic phase. A similar change is observed in the lamellar to nematic transition, however, the detailed behavior at this transition showed some dependence on the history of the sample. The expansion coefficients decrease at the transitions. Considerable pretransitional behavior is observed about the lamellar-to-nematic transition.

Photochemically induced phase transitions in the system cetyltrimethyl-ammonium bromide-water containing N-methyl-N,N-diphenylamine

Phase transition temperatures from lyotropic liquid crystals to the isotropic micellar solution of the system cetyltrimethylammonium bromide-water (CTAB-H2O) were measured in the presence of 0.1-0.9 weight % of N-methyl-N,N-diphenylamine (MPA). They were determined by optical and viscometric methods and were found to increase as a function of MPA concentration in solutions containing 21 and 23 weight % of CTAB. This effect was reversed when MPA was in situ photochemically converted to N-methylcarbazole, allowing photochemically induced phase transitions.

Viscosity and Phase Behavior of Petroleum Sulfonate Solutions in the Liquid Crystalline Region

Summary Aqueous solutions of two petroleum sulfonate surfactants, a pure sulfonate surfactant and one mixed with an ethoxylated sulfate surfactant, were studied with polarizing microscopy, polarized light screening (PLS), and viscometry. The same sequence of phases was seen with increasing salinity for the various surfactants—i.e., transformation from an isotropic micellar solution to a lamellar liquid crystalline phase to an isotropic phase that scattered light and exhibited streaming birefringence. Addition of calcium ions to the petroleum-sulfonate/ethoxylated-sulfate mixtures led to the same basic sequence of transformations, but the effect of calcium was about 11.5 times as great as that of sodium on a molar basis. Many small crystalline particles were also observed when calcium was present. A cone-and-plate viscometer was used to measure the apparent viscosity of the various solutions. A maximum in apparent viscosity was always found in the transition region between a dispersion of spherulitic liquid crystalline particles in an aqueous phase and a single liquid crystalline phase. The maximum occurred whether the transition was brought about by changes in salinity, divalent cation concentration, oil content, or other compositional variables. Apparent viscosity generally decreased with increasing temperature, although dependence on temperature was not monotonic at high salinities. Apparent viscosity decreased with increasing shear rates and was time-dependent at a given shear rate. At low salinities, apparent viscosity generally decreased with time. At high salinities, apparent viscosity frequently increased with time.

Measurements of the conductivity and relaxation times for the micellar nematic phase of the system ammonium perfluorononanoate/H2O

Measurements of the electric conductivity for two mixtures of ammonium perfluorononanoate and H2O are presented. The molar ratios for the two mixtures are 0.0159 (sample S2) and 0.0112 (sample S3). The mixtures show a nematic (NL) range about 8 °C wide, between a lamellar smectic and an isotropic micellar solution. The conduction is predominantly due to the NH4+ ions, and it is estimated that about 50% of the NH+4 ions have free mobility. At the same reduced temperature in the NL phase, the lower concentration mixture is more anisotropic, indicating larger micelles for the lower concentration. The reorientation of the director of the NL phase in a magnetic field is also measured. Near the NL to isotropic transition the relaxation times at 10 kG are 30 s for S2 and 80 s for S3. The divergence behavior of the relaxation times at the NL to lamellar transition is different for the two samples. Also, at corresponding temperatures, the relaxation time for the lower concentration is longer than the high concentration mixture. It is also observed that in the lamellar phase, increasing the temperature may lead to undulation of the layers.

ChemInform Abstract: The Electric Conductivity of the Lamellar Smectic, the Micellar Nematic, and the Isotropic Micellar Solution of Ammonium Perfluorononanoate in Water.

Chemischer InformationsdienstVolume 17, Issue 16 Article ChemInform Abstract: The Electric Conductivity of the Lamellar Smectic, the Micellar Nematic, and the Isotropic Micellar Solution of Ammonium Perfluorononanoate in Water. P. J. PHOTINOS, P. J. PHOTINOSSearch for more papers by this authorA. SAUPE, A. SAUPESearch for more papers by this author P. J. PHOTINOS, P. J. PHOTINOSSearch for more papers by this authorA. SAUPE, A. SAUPESearch for more papers by this author First published: April 22, 1986 https://doi.org/10.1002/chin.198616079AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume17, Issue16April 22, 1986 RelatedInformation

Phase behaviour and structure of a non-ionic discoidal amphiphile in water

The phase behaviour and structure of mixtures of a novel non-ionic discoidal amphiphile, 2,3.6,7,10,11-hexa-(1,4,7-trioxaoctyl)-triphenylene, and water have been investigated using deuterium NMR spectroscopy and X-ray diffraction. The feature of special interest is the occurrence of a nematic phase, intermediate to an isotropic micellar solution at higher temperatures and a columnar hexagonal phase at lower temperatures. This nematic phase exists over wide concentration (0.1 to 0.5 volume fraction of amphiphile) and temperature intervals. The molecules are stacked in columnar (rod-shaped) aggregates. In the isotropic micellar solution and nematic phase the length of the micelle is of the order of the centre-to-centre separation.

Order-disorder transitions in solutions of discoid micelles

X-ray scattering, electrical conductivity and NMR measurements are presented for a sample of caesium pentadecafluoroctanoate (CsPFO) (55 per cent by weight)/water (2H2O). A first order lamellar to nematic phase transition occurs at 325.13 (1) to 325.50 (1) K and a first order nematic to isotropic micellar solution transition occurs at 330.23 (1) to 330.83 (1) K. The fundamental mesogenic particle is shown to be a discrete discoid micelle in all three phases, that is, the lamellar phase consists of planes of discoid micelles. The thickness of the micelle is of the order 2.2 nm. In the isotropic micellar solution, the average diameter of the micelle grows slowly on cooling. At the isotropic to nematic transition, it increases discontinuously from 5.26 nm (NA = 88 ) at the upper boundary to 5.82 nm ( N A = 113) at the lower boundary, but there is no discontinuity in size at the nematic to lamellar transition where the diameter is 6.38 nm (N A =140). The growth of the micelle in the nematic phase appears to be driven mainly by the variation with temperature of the orientational order parameter (this is 0.35 at the nematic to isotropic transition and 0.72 at the nematic to lamellar transition). This behaviour is as predicted by the theories of Gelbart et al., yet the transition to the lamellar phase is not driven by the predicted explosive growth of the micelles into bilayers. The X-ray scattering patterns are characteristically different from those generally observed in the analogous thermotropic nematic and smectic A phases. It is argued that this is because the micelles (volume fraction 0.35) are relatively loosely packed: in fact, in all of the three phases they may well undergo large amplitude uncorrelated reorientational fluctuations. Short range orientational correlations are consequently either absent or very limited in their extent. This is manifest in the unexpectedly large values (0.92 to 0.71 in the nematic phase) of the orientational order parameters obtained from the X-ray measurements ; it is suggested that these order parameters are mainly determined by the long-range collective director fluctuations. Thus, the model which emerges for the nematic phase is one in which the individual orientational fluctuations of the micelles are essentially decoupled from the collective director fluctuations.

The electric conductivity of the lamellar smectic, the micellar nematic, and the isotropic micellar solution of ammonium perfluorononanoate in water

We present electric conductivity measurements on a mixture of 25 wt. % ammonium perfluorononanoate in H2O. The system shows a lamellar smectic phase up to 26.3 °C, followed by a nematic phase consisting of disk-like aggregates, which at 34.2 °C transforms to an isotropic micellar solution. The relative anisotropy of the conductivity increases from ∼0.07 at 34 °C to ∼0.29 at 26.3 °C. There is no discontinuity, but a small change in slope occurs at the nematic–smectic transition. The experimental results, interpreted in terms of structural models for the two anisotropic phases, shows that the aggregates in the nematic phase have diameter to thickness ratios, decreasing from about 8.3 at the lamellar to nematic transition, to about 4.0 at the transition to the isotropic phase. We estimate that about 30% of the total area are disrupted by holes or channel-like defects. The results are in agreement with previous studies on a mixture of decylammonium chloride/NH4Cl/H2O. It is also indicated that increasing the size of the aggregates increases the binding of the counterions to the aggregates.

Phase equilibria in four lysophosphatidylcholine/water systems. Exceptional behaviour of 1-palmitoyl-glycerophosphocholine.

The phase equilibria in four lysophosphatidylcholine/water systems were investigated at different temperatures. Each of the 1-palmitoyl-, 1-stearoyl-, 1-oleoyl- and 1-linoleoyl-sn-glycero-3-phosphocholines was dispersed in heavy water at different concentrations. The phase structures were determined by 2H-, 14N- and 31P-NMR, polarization microscopy and low-angle X-ray diffraction. The phase diagrams of the oleoyl and linoleoyl systems were quite similar. At room temperature and with decreasing water content the isotropic micellar solution was followed by a hexagonal phase and then a cubic phase. Finally the lamellar phase appeared before the region of hydrated crystals. The same sequence of phases was observed in the stearoyl system at elevated temperatures. The palmitoyl system differed from the others: here a cubic phase followed after the micellar solution, then came a hexagonal phase and after this a lamellar phase. In general the lysophosphatidylcholines seem to behave similarly to the many soaps and detergents as they show the same sequence of isotropic micellar solution, hexagonal phase, lamellar phase with interspersed cubic phases. The presently established phase diagrams demonstrate that the major lysophosphatidylcholines which may be generated by phospholipase A2 in mammalian cell membranes, viz. 1-palmitoyl- and 1-stearoyl-glycerophosphocholines differ greatly in their packing properties. The extraordinary ability of 1-palmitoyl-glycerophosphocholine to form a cubic phase in equilibrium with a micellar solution is of particular interest with regard to the possible occurrence of cubic structures in biomembranes during the process of fusion.

Density and Susceptibility Measurements on a Micellar Nematic System

Abstract The densities and diamagnetic susceptibilities in the nematic and isotropic ranges of two mixtures of decylammonium chloride, ammonium chloride, and water are reported. The mixtures have a lamellar smectic phase, a nematic phase, and an isotropic micellar solution. The smectic-nematic transition is second order, the nematic-isotropic transition first order. The density does not show a discontinuous change at the nematicisotropic transition, and the expansion coefficients of the nematic and isotropic regions are the same within error limits. The diamagnetic susceptibility in the isotropic range and the susceptibility perpendicular to the optical axis in the nematic range were determined using the Gouy method. The diamagnetic anisotropy of the nematic range was derived. It varies from 2 X10−9 near the nematic-isotropic transition to 5 × 10−9 cgs near the nematic-smectic transition.

Resistivity Measurements on Aligned Amphiphilic Liquid Crystalline States

Abstract We measured the resistivity of a ternary liquid mixture consisting of decylammoniumchloride, ammoniumchloride and water (45:5:50 wt%). The mixture forms a nematic phase between 41°C and 61°C; below 41°C a neat soap, and above 61°C an isotropic micellar solution. The resistivity decreases with increasing temperature. In the nematic and in the neat soap phases the resistivity is anisotropic, and it is higher for currents parallel to the director. The anisotropy increases strongly with decreasing temperature, due to a much stronger temperature dependence of the resistivity parallel to the director. The changes accompanying the phase transitions are small. The surprisingly small change of the resistivity parallel to the director at the nematic to neat soap transition indicates that the lamellae in the neat soap contain a large number of defects.

Are “nematic” amphiphilic liquid crystalline mesophases thermodynamically stable?

Microscopy and deuterium NMR spectroscopy are employed to demonstrate the existence of a thermodynamically independent nematic amphiphilic mesophase in mixtures of perfluoro-octanoate and water between 37.0 to 87.0% by weight of 2H 2O and 284.0 to 348.3 K at 1 atmosphere pressure. This phase is in equilibrium with an isotropic micellar solution and a smeetic lamellars mesophase to, respectively, high and low temperatures. The lamellar to nematic transition line changes from first to second order at a tricritical point corresponding to 42.5% of 2H 2O and 328.0 K, whilst the nematic to isotropic micellar solution transition is first order at all compositions. The measurements suggest the nematic phase is a solution of disc shaped micelles which orient with their unique axis parallel to the direction of an applied magnetic field.

The Structure of Lyotropic Nematic Decylammoniumchloride and Bromide Systems by PMR of Monomethyltin Complexes and by Microscopic Studies

Abstract The pmr spectrum of methyltintrichloride in aqueous micellar solutions of decylammoniumchloride and KCl, and of decylammoniumbromide and KBr was investigated. The large scalar SnH couplings of 134.0 Hz and 130.2 Hz respectively indicate the formation of six coordination complexes CH3SnCl5 - - and CH3SnBr5 - - in the micellar solutions, but the geometrical structure of the CH3Sn moiety is little affected by the complex formation. The complexes orient with their symmetry axis preferably parallel to the nematic axis. In microscopic studies on selected mixtures a reversible first order phase transition was observed between nematic and isotropic micellar solution at about 45°C and a reversible transition between a lamellar smectic phase and the nematic phase at about 30°C that appears to be of second order. The optical observations and the orientation of the methyltin complex indicate that the nematic solutions have micelles of a bilayer structure.

Phase behavior and structural characteristics of hydrated bovine brain gangliosides

Hydrated bovin brain gangliosides have been studied by differential scanning calorimetry, X-ray diffraction, and polarized light microscopy. Over the hydration range 18–50 wt.% H 2O, mixed brain gangliosides exhibit a hexagonal mesophase structure, in which the ganglioside molecules form hexagonally packed rod-like structures. The apolar lipid chains radiate from the center of the rods, with the sugar groups on the cylinder surface in contact with water. At higher water contents, an isotropic micellar solution is formed. Over the hydration range 20–30 wt.% H 2O, two small thermal transitions with peak maxima at 30°C and 46°C are observed by differential scanning calorimetry. These transitions broaden and move apart in temperature as the hydration is increased to 50 wt.% H 2O. X-ray diffraction data indicate that this double transition is associated with a hydrocarbon chain rearrangement from a disordered state to another, possibly more disordered, state. Thus, the gangliosides, although membrane lipid components, have physical characteristics which are very different from those of the membrane phospholipids.

The aqueous cetyl trimethylammonium bromide solutions

The dependence on the concentration of the density, viscosity, refractive index, and light scattering has been studied in aqueous solutions of cetyltrimethylammonium bromide between 0.036% (c.m.c.) and 26%. The results are discussed in relation to results of other studies. Above the c.m.c. there are more or less spherical, strongly hydrated micelles composed of about 95 CTAB molecules. From 9% to 11% upwards the micelles are deformed to rod-shaped micelles owing to the increasing crowding in the solution. At 26% the isotropic micellar solution is transformed via a narrow two-phase region to mesomorphous middle soap with rod-shaped hydrated CTAB aggregates in hexagonal array.

Biophysics of lipid associations: III. The quaternary systems lecithin-bile salt-cholesterol-water

Following upon the ternary systems studied in Parts I and II of this work, the quaternary systems formed of lecithin, bile salt, cholesterol and water are considered in this third part. The different phases formed by the quaternary mixtures have been examined by both the ordinary and the polarizing microscopes, and their paracrystalline molecular structure determined by X-ray diffraction. The construction of the quaternary diagram is described. It represents the composition of the regions of existence of single phases or the equilibrium of the different phases: isotropic micellar solution, paracrystalline lamellar, hexagonal and cubic phases. These phases are identical with those obtained with the ternary systems lecithin-bile salt-water. Cholesterol can be incorporated into each of them without any important modification in their structure, and no new phase appears as a consequence of this addition of cholesterol. The solubilization of cholesterol obtained by the simultaneous presence of lecithin and bile salt is stressed, and the application of these facts to the study of bile and the formation of gallstones is discussed.