Showing papers on "Lyotropic liquid crystal published in 1974"
TL;DR: In this article, the critical magnetic field for the cholesteric to nematic transition of a pure lyotropic liquid crystal solution of an α-helical polypeptide, polyγ-benzyl-Lglutamate, was determined by direct microscopic observation of the changing pitch of the structure as a function of magnetic field strength.
Abstract: We have determined the critical magnetic field for the cholesteric to nematic transition of a pure lyotropic liquid crystal solution of an α‐helical polypeptide, poly‐γ‐benzyl‐L‐glutamate, by direct microscopic observation of the changing pitch of the structure as a function of magnetic field strength. The course of the transition is well accounted for by the theory of deGennes. An independent measurement of the anisotropy of diamagnetic susceptibility allows the determination of κ22, the twist elastic constant of the medium.
29 citations
Patent•
23 Dec 1974
TL;DR: A suspension of solid particles in an organic or aqueous liquid comprises a lyotropic liquid crystal as suspension stabilizer as discussed by the authors, which can be used as a stabilizer for any liquid.
Abstract: A suspension of solid particles in an organic or aqueous liquid comprises a lyotropic liquid crystal as suspension stabilizer.
24 citations
TL;DR: In this paper, spin-labeled fatty acids are used to investigate a lyotropic mesophase in which the amphiphilic molecules are arranged in cylindrical rods and a homogeneous ordering of the cylinders is obtained by sucking the liquid crystalline phase in glass capillaries.
Abstract: Spin labeled fatty acids are used to investigate a lyotropic mesophase in which the amphiphilic molecules are arranged in cylindrical rods. A homogeneous ordering of the cylinders is obtained by sucking the liquid crystalline phase in glass capillaries. This considerably simplifies the epr spectra. The lipid molecules in the cylinders undergo fast rotations around their long axes with a correlation time of approximately 10−10 sec and slower rotations around the axis of the cylinder. The latter effect is responsible for distinct differences between the spin label spectra of cylinder and bilayer phases. The hydrocarbon chains in the cylinders are flexible and the order parameter decreases from the polar surface towards the interior of the cylinders. The microviscosities of both phases are about equal and amount to approximately 0.05 poise.
24 citations
TL;DR: In this paper, the authors reviewed the thermodynamic aspects of the polymorphism of liquid crystals to enable a classification to be drawn up on the basis of miscibility criteria in binary systems.
Abstract: Thermodynamic aspects of the polymorphism of liquid crystals are reviewed to enable a classification to be drawn up on the basis of miscibility criteria in binary systems. Liquid-crystalline modifications are classified as nematic and several types of smectic rn odifications. Structural ii vestigations so far seem to confirm this scheme The topology of binary isobaric phase diagrams is examined and the interpretation of intermediate mixed phases discussed Quantitative thermodynamic data on solutes in 1iquidcrystaiiine phases seem to reflect the degree of order of modification Transition enthalpies and entropies are reported on and It is concluded that polymorphism of liquid crystals gives opportunity for extending thermodynamic investigations to various mixed phases and their transition processes. !NTRCDUCTION Liquid crystals are states of condensed matter. Using the conventional criteria of thermodynamics they are characterized as phases. The term liquid crystal or crystalline liquid refers to phenomenological characteristics The anisotropy of their properties has been used to distinguish these states from normal isotropic liquids, although many properties show a behaviour typical for liquids In other cases it is not strictly possible to make a clear distinction between this state and the solid state. However, the conventional notation represents well the nost essential features and functions of these states. The formation of liquid-crystalline states can be observed in organic onecomponent systems withm a range of pressure and temperature which is typical for the individual compounds Adding a second and further components, the formation of a homogeneous mixture is frequently observed (mixed liquid crystals, liquid-crystalline mixtures or solutions. If the second component also forms a liquid-crystalline phase the formation of a complete series of liquid-crystalline mixtures can take place. These systems are called thermotropic liquid crystals. A large group of liqwd-crystallme states comprises the lyotropic liquid crystals which originate from the interaction of an organic component with a solvent which itself does not form liquid-crystalline states e g with water Liquid-crystalline structures are here generated by a specific inter action with the solvent. Typical examples are amphiphile substances capable
24 citations
TL;DR: In this article, the effect of double quantum transitions on the interpretation of deuteron NMR spectra of unoriented liquid crystals was investigated. And the derived spectral intensities demonstrate that it is necessary to take double quantum transition into account in the interpretation.
18 citations
TL;DR: In this article, the authors examined the asymmetric diffusion of small molecules in a liquid crystal host via three models: DASH, LASH and CASH, and found that DASH is a better representation of the diffusion asymmetry than LASH for the low liquid crystal densities examined on the computer.
Abstract: The asymmetric diffusion of small molecules in a liquid crystal host is examined via three models. The small molecules are represented by spheres and the liquid crystal host by aligned cylinders. DASH is a continuum model which allows one to use the results of electrical conductivity problems to calculate the diffusion coefficient. LASH is an extension of polymer lattice counting models. CASH is a molecular dynamics computer simulation which provides experimental data to check the analytical models. It is found that DASH is a better representation of the diffusion asymmetry than LASH for the low liquid crystal densities examined on the computer. The cylinder sphere pair correlation function is also calculated in CASH and this gives evidence for liquid order around the liquid crystals.
4 citations
TL;DR: In the presence of sufficiently strong electric or magnetic fields, polyγ-benzyl-L-glutamate (PBLG) undergoes a mesomorphic phase transition to nematic order as mentioned in this paper.
Abstract: Above a critical concentration in certain solvents poly-γ-benzyl-L-glutamate (PBLG) forms a lyotropic liquid crystal of the cholesteric structure. In the presence of sufficiently strong electric or magnetic fields this liquid crystal undergoes a mesomorphic phase transition to nematic order. Reported are the results of our long term observations of bulk samples of liquid crystalline PBLG subjected to strong magnetic fields. We have observed visually magnetohydrodynamic processes that occur on several very different time scales: (a) the slow cholesteric-nematic phase transition, (b) a more rapid reorientation in the acquired nematic condition, and (c) a critical orientation of nematic PBLG with unusual anisotropic optical effects and high, but directional, thermal sensitivity. The phenomena are accounted for in terms of molecular order and dynamics of the associated polypeptide helices.
2 citations
TL;DR: In this article, the critical magnetic field for the cholesteric-nematic phase transition of the lyotropic liquid crystal poly- gamma -ethyl-L-glutamate in ethyl acetate has been determined by the use of light diffraction patterns.
Abstract: The critical magnetic field for the cholesteric-nematic phase transition of the lyotropic liquid crystal poly- gamma -ethyl-L-glutamate in ethyl acetate has been determined by the use of light diffraction patterns. In spite of the variation of the zero-field helix pitch with concentration, the critical field is nearly constant at about 29 kOe.
2 citations
01 Jan 1974
TL;DR: In this paper, some avenues for evaluating the intermolecular energies as a function of the type of packing, the role of dispersing medium in bringing about phase transitions and the influence of a specific molecule, cholesterol, in changing physical properties of the system were discussed.
Abstract: The salient conformational features and associated energies in dimyristoyl lecithin have been considered elsewhere (Mishra and Roper, 1973). We point out here (a) some avenues for evaluating the intermolecular energies as a function of the type of packing, (b) possible role of dispersing medium in bringing about phase transitions and (c) the influence of a specific molecule, cholesterol, in changing physical properties of the system.
1 citations
01 Jan 1974
TL;DR: The structure of lyotropic mesophases is critically influenced by the nature and relative amount of dispersing medium as discussed by the authors, which is sufficient to direct one's attention to the nature, disposition and magnitude of intemolecular forces, attractive as well as repulsive, as the probable determinants of stability and phase transitions in these systems.
Abstract: The structure of lyotropic mesophases is critically influenced by the nature and relative amount of dispersing medium. This fact alone is sufficient to direct one’s attention to the nature, disposition and magnitude of intemolecular forces, attractive as well as repulsive, as the probable determinants of stability and phase transitions in these systems. This suspicion is further strengthened by the fact that structural classes in these systems are much fewer than the compounds involved (Mishra, 1972)pointing out again that relatively general forces as opposed to highly specific orbital configurations and characteristics of atoms, might be directly involved in the production of this state. Indeed, the presence of large apoiar segments with relatively weak residual atomic charges and polar ends stresses again the need to search in the same direction. It would seem that the dispersing medium brings about the phase changes by affecting the geometric disposition and magnitudes of the intermolecular forces.
1 citations
TL;DR: In this paper, the mesophase transformations exhibited by supersaturated aqueous solutions of four different lithium sulfoacetate esters were carried out by selective extraction of water from each of them into the support medium and it was concluded that the stochastic nature of the transformations must be a result of an energy barrier.
Abstract: Studies on the mesophase transformations exhibited by supersaturated aqueous solutions of four different lithium sulfoacetate esters were carried out. The concentration changes required to bring about these transformations in a population of non-communicating droplets were created by selective extraction of water from each of them into the support medium. By analogy with crystal nucleation from solution, it was concluded that the stochastic nature of the transformations must be a result of an energy barrier. The magnitude of each energy barrier was not estimated because appropriate reference points are not available.
01 Jan 1974
TL;DR: In this article, it was shown that poly(γ-benzyl-L-glutamate) (PBLG) can exist as rigid, rod-like α-helical molecules, in contrast with the random coil conformation adopted by most other synthetic polymers in solution.
Abstract: Some twenty years ago it was found that synthetic polypeptides, Open image in new window , can exist as rigid, rodlike α-helical molecules, in contrast with the random coil conformation adopted by most other synthetic polymers in solution. This observation with its implications in the study of protein structure stimulated a concentrated and sustained investigation of the dilute solution (1–5 wt.% polymer) properties of this class of polymers. In more concentrated polypeptide solutions (10–15 wt.% polymer), poly (γ-benzyl-L-glutamate) (PBLG; R = CH2CH2COOCH2C6H5), forms a lyotropic liquid crystal. Robinson1 extensively characterized the PBLG liquid crystal and found similarities between its supra-molecular structure and the structure existing in thermotropic cholesteric liquid crystals.