Showing papers on "Lyotropic liquid crystal published in 1985"
TL;DR: In this article, an expression for the energy of chiral interaction between polypeptide molecules in a solution is obtained using the general theory of van der Waals-Lifshitz forces between macromolecules.
37 citations
TL;DR: In this paper, the internal structure of a ribbon-like aggregate in an ordered mesophase with rectangular symmetry formed by two amphiphiles, sodium decyl sulfate and decanol, in presence of water, is investigated by neutron scattering.
Abstract: The internal structure of a ribbon-like aggregate in an ordered mesophase with rectangular symmetry formed by two amphiphiles, sodium decyl sulfate and decanol, in presence of water, is investigated by neutron scattering. Our results show that the two amphiphiles are not uniformly distributed within the aggregate. Their relative concentration is modulated according to the local interfacial curvature of the aggregate. Such a concentration/curvature relationship may be an important point to understand the shape of the aggregates and therefore the polymorphism of lyotropic liquid crystals Etude par diffusion de neutrons de la structure interne d'un agregat en forme de ruban dans une mesophase ordonnee a symetrie rectangulaire formee par deux amphiphiles, decylsulfate de sodium et decanol, en presence d'eau. Distribution non uniforme des deux amphiphiles dans l'agregat, leur concentration relative variant localement selon la courbure interfaciale de l'agregat
36 citations
01 Oct 1985
TL;DR: In this article, the tetramethylammonium salt of perfluoronononanoic acid (TMPFN = C8F17COON(CH3)4) in D2O forms a nematic phase in the temperature range between 32 and 37°C.
Abstract: A solution of 30% by weight of the tetramethylammonium salt of the perfluorononanoic acid (TMPFN = C8F17COON(CH3)4) in D2O forms a nematic phase in the temperature range between 32 and 37°C. The nematic phase was aligned and cooled down to 25°C in a magnetic field of 1.63 and 1.26 T. The structure of the aligned sample was studied with small angle neutron scattering (SANS) at different temperatures. In the liquid crystalline phase first and second order Bragg-peaks were observed. This phase consists mainly of liquid crystals build by sheets of disk-like TMPFN micelles alternating with layers of D2O. The lattice parameter is around 75 A at 25°C. An order parameter S near 1 was determined by a thorough analysis of a rocking experiment. Besides the Bragg-peaks further scattering features were observed: A Debye-Scherrer like ring probably related to disclike micelles and a ridge related to a unknown aligned structure. The SANS-pattern was examined in an temperature range between 25 and 45°C.
32 citations
TL;DR: In this paper, the orientational distributions of fluorescent probe molecules in ground and excited states are generally not equal, and it is concluded that the order parameter of a fluorophore in a microscopically anisotropic and macroscopically isotropic system cannot generally be determined directly from the emission anisotropy.
29 citations
TL;DR: In this article, the self-diffusion of water has been measured in unaligned Lα mesophases of potassium palmitate and water, using the pulsed field gradient NMR technique (PFG NMR).
25 citations
01 Jan 1985
TL;DR: In this paper, the behavior of paraffinic chains of amphiphilic molecules such as soaps, detergents and lipids in aggregates of the liquid crystalline and micellar phases has been studied in detail with NMR.
Abstract: The behaviour of the paraffinic chains of amphiphilic molecules such as soaps, detergents and lipids, in aggregates of the liquid crystalline and micellar phases has been studied in detail with NMR. These studies demonstrated the dynamical disorder of the chains, particularly that introduced by the conformation changes of their carbon-carbon skeleton. In the most studied case, that of the lamellar phases with flat amphiphile/water interfaces, they also gave direct access to the disorder profile of a chain, making possible a description of its anisotropic behaviour around the local normal to the interface. A very limited number of studies only has been devoted to hexagonal and micellar phases, with cylindrical and spherical interfaces, where one might expect, on purely intuitive grounds, important changes in the disorder profile imposed by the curvatures of the interfaces.
21 citations
TL;DR: Magnetic-birefringence measurements were performed in the nematic phase of the binary lyotropic liquid crystal cesium perfluoro-octanoate and water within 75 mK of the superheating limit, indicating that director fluctuations may contribute a significant multiplicative factor to the average order parameter.
Abstract: Magnetic-birefringence measurements were performed in the nematic phase of the binary lyotropic liquid crystal cesium perfluoro-octanoate and water within 75 mK of the superheating limit. Several results were obtained: (1) The induced birefringence was linear in H for small H, but showed significant deviations from linearity for Hg5 T; (2) the elastic constant was found to be very small near the transition, indicating that director fluctuations may contribute a significant multiplicative factor to the average order parameter; and (3) the order-parameter exponent \ensuremath{\beta}=0.34\ifmmode\pm\else\textpm\fi{}0.06. This last result is examined in the context of a mean-field theory with higher-order terms in the free-energy expansion and in the context of the d=3, N=5 N-vector model.
20 citations
TL;DR: In this paper, the phase diagram and results from magnetic susceptibility measurements in the isotropic phase are presented for the lyotropic liquid crystal cesium perfluoro octanoate+water in the presence of an added salt CsCl.
Abstract: The phase diagram and results from magnetic susceptibility measurements in the isotropic phase are presented for the lyotropic liquid crystal cesium perfluoro octanoate+water in the presence of an added salt CsCl. Based upon the evolution of the Cotton-Mouton coefficient and in the context of an Onsager-type calculation we speculate on the micellar conformation as a fonction of electrolyte concentration Diagramme de phase et mesures de susceptibilite magnetique de la phase perfluorooctanoate de cesium+eau en presence de sel de CsCl. Structure des micelles en fonction de la concentration d'electrolyte
18 citations
TL;DR: In this article, a micelle distortion model for the generation of cholesteric behavior was discussed in terms of a micro-drone distortion model and the results compared to those for the dodecanoate amphiphile.
Abstract: Cholesteric lyotropic liquid crystals prepared from the potassium salts of N-hexadecanoyl-l-proline and N-dodecanoyl-l-alanine have been studied as mixed systems with tetradecyltrimethylammonium bromide. The twist, induced by the chiral centre, was studied as a function of the mole fraction, X, of chiral amphiphile in total amphiphile. It was found that the twist showed a maximum for the neutrally charged mesophases (X = 0.5) and that for the pure chiral systems (X = 1.0) the alaninate system showed a much larger twist than the corresponding prolinate material. The results were discussed in terms of a micelle distortion model for the generation of cholesteric behaviour. Alkali metal ion binding to the carboxylate groups of these amphiphiles was investigated and the results compared to those for the dodecanoate amphiphile. A three site model of binding was used in order to determine the number of liganding amphiphiles in the pure anionic mesophase (X = 1.0). It was found that the number decreased ...
17 citations
TL;DR: Aqueous binary systems of potassium oleate and sodium dodecyl sulphate exhibit an hexagonal phase at low surfactant concentrations and appropriate temperatures as discussed by the authors, which is followed by a distorted hexagonal structure.
Abstract: Aqueous binary systems of potassium oleate and sodium dodecyl sulphate exhibit an hexagonal phase at low surfactant concentrations and appropriate temperatures. However, in the former system the phase is succeeded at higher surfactant concentrations by the so-called rectangular phase, while in the latter system a distorted hexagonal phase follows. X-ray diffraction results for these systems indicate that the rectangular phase is a consequence of axial growth of the hexagonal-phase surfactant cylinders with surfactant content at substantially constant radius. Water in the hexagonal phase occupies positions other than along and between cylinder lengths. Radial growth of cylinders leads to the distorted hexagonal structure. The cylinder growth and transformation behaviours are associated with characteristics of the respective molecular structures.
16 citations
TL;DR: It was found that (T-${T}^{\mathrm{*}}$)C is a weakly decreasing function of concentration, indicating a significant concentration dependence of the micelle structure.
Abstract: The concentration and temperature dependences of the Cotton-Mouton coefficient C for the binary mixture cesium perfluoro-octanoate and water close to a nearly-second-order nematic-isotropic transition are reported. It was found that (T-${T}^{\mathrm{*}}$)C is a weakly decreasing function of concentration, indicating a significant concentration dependence of the micelle structure.
TL;DR: In this article, the cholesteric textures displayed by aqueous mixtures of 1:2: 1 D-(2)-octylammonium chloride:decylammium ch1oride:salt (NH4, Cl, KCl, LiCl, NaCl) were investigated for the dependence of the pitch upon such variables as the nature of the salt cation, salt concentration, pH and temperature.
Abstract: D-(2)-octylammonium chloride has been observed to form lyotropic liquid crystals in aqueous solutions. Cholesteric, nematic, and smectic phases will form depending on concentration, co-amphiphile content, ionic environment and temperature. The cholesteric textures displayed by aqueous mixtures of 1:2: 1 D-(2)-octylammonium chloride:decylammonium ch1oride:salt (NH4, Cl, KCl, LiCl, NaCl) were investigated for the dependence of the pitch upon such variables as the nature of the salt cation, salt concentration, pH and temperature. The investigative methods used include magnetic field orientation, differential scanning calorimetry, laser diffraction and optical microscopy. The results obtained include the dependence on the concentration of chiraldopants and compensation effects.
TL;DR: In this paper, the free energy of ternary microemulsions has been studied in the Aerosol OT-water-decane system and the phase diagram has been determined at 25°C.
Journal Article•
Dissertation•
01 Jan 1985
TL;DR: In this article, the structural role played by the fatty alcohol in the polymorphism of this phase diagram was investigated and the relationship between the local interfacial curvature of the aggregates and the respective local concentrations of both amphiphiles was found.
Abstract: The "lyotropic liquid crystal" phases of the phase diagram obtained from mixtures of sodium decylsulfate, decanol and water at 23°C have been studied through optical microscopy and X-ray diffraction measurements. New lyotropic phases, such as 2D rectangular phases of various symmetry and lamellar phases containing structural defects showed up during this study. Questions were raised about the structural role played by the fatty alcohol in the polymorphism of this system. Thermal neutron scattering experiments revealed a close relationship between the local interfacial curvature of the aggregates and the respective local concentrations of both amphiphiles: the alcohol is preferentially located in those parts of the aggregates where the interfacial curvature is low, whereas the soap concentration is higher in the parts where the interfacial curvature is more pronounced. Such a curvature/concentration relationship is indeed a point supporting a discussion about the physics of the phase transformations which take place in the concentrated region of this phase diagram.
01 Jan 1985
TL;DR: The macroscopic structure of the mesophase which obtains for a particular surfactant-water mixture is governed by the size and shape of the amphiphilic aggregate as discussed by the authors.
Abstract: The macroscopic structure of the mesophase which obtains for a particular surfactant-water mixture is governed by the size and shape of the amphiphilic aggregate. The latter is, in turn, determined by the molecular interactions, especially those at the aggregate-water interface and which control the surface curvature (1). These can be probed by studying the interaction and binding of both counterions and water at this interface using NMR methods. Arguably, the most informative quantities to measure are quadrupolar splittings of the alkali metal ions and 2H and 17O in labelled water. The object of this chapter is to critically assess the information obtainable from such measurements.
01 Jan 1985
TL;DR: In this article, the rotational diffusion coefficients of surfactant molecules are obtained from the temperature and frequency dependences of the 31P longitudinal relaxation which depends on the chemical shift anisotropy and on the dipolar coupling with nearby protons.
Abstract: Some specific applications of NMR to lyotropic liquid crystals are reported on examples taken from studies in progress on sodium alky 1-phosphate/water systems. The reorientation dynamics of intersticial water is obtained from the splittings and relaxation rates of 1H, 2H and 17O. The molecular order parameters and alkyl chain conformation are derived from 2H quadrupolar splittings and interpreted in term of intermolecular interaction confining the molecules in restricted volumes. The rotational diffusion coefficients of surfactant molecules are obtained from the temperature and frequency dependences of the 31P longitudinal relaxation which depends on the chemical shift anisotropy and on the dipolar coupling with nearby protons.