Download The Physics of Lyotropic Liquid Crystals: Phase Transitions by Antônio M. Figueiredo Neto, Silvio R. A. Salinas PDF

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By Antônio M. Figueiredo Neto, Silvio R. A. Salinas

Figueiredo Neto and Salinas (physics, U. of Sao Paulo) notice that soaps were with us for numerous millennia, and that their use in washing is without delay with regards to basic strategies in self- assembling and ordering. As surfactant molecules, they're partially water-soluble and in part oil-soluble. those lyotropic platforms are first-class examples of polymorphism and section modifications, counting on their temperature, strain, and different physico-chemical parameters. The authors study the most experimental proof and strategies of lyotropic structures, together with their mesophases and functions and the fundamental suggestions of section transitions. They study section diagrams of lyotropic combinations, part transitions among periodically geared up lytropic stages, isotropic micellar and bicontinuous levels, nematic and cholesteric stages, and the lyotropic stages in a single to 3 dimensions. additionally they learn contemporary advancements, equivalent to microemulsions and Langmuir-Blodgett motion pictures.

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Additional resources for The Physics of Lyotropic Liquid Crystals: Phase Transitions and Structural Properties

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Based upon NMR experiments [95], measurements of the optical birefringence [49], and on the sign of the anisotropy of the diamagnetic susceptibility (∆χ = χ − χ⊥ , where χ and χ⊥ are the susceptibilities parallel and perpendicular to the director of the phases), the lyotropic nematics were classified as type I and type II (no biaxial phases had yet been observed at that time). Type I mesophases have ∆χ > 0, negative optical anisotropy (n −n⊥ < 0, where n and n⊥ are the indices of refraction parallel and perpendicular to the director, respectively) and, in the presence of a strong enough magnetic field (B 10 kG), the director n aligns parallel to the field.

Two mixtures were studied with respect to their local order and structure in nanometric length scales [128]: sodium decylsulfate, 1-decanol, water, and brucine sulfate heptahydrate, called BS; and potassium laurate, 1-decanol, water, and d-2-octanol. The phase diagram of these mixtures display a ChC phase that unwinds the cholesteric helix in the presence of sufficiently strong magnetic fields. Comparing the diffraction patterns of field-unwind ChC mesophases with those of the corresponding NC phases, it was possible to check that the pseudo-lamellar order observed in nematics is still present in cholesterics.

The Landau point, at the convergence of a first-order and two second-order transition lines, is experimentally accessible in the case of this mixture [83]. From the analysis of early X-ray [59,60] and neutron [47] diffraction results, the micelles in the NC and ND nematic phases were assumed to be prolate and oblate ellipsoids, respectively. These conclusions were also based on the equivalence between the frame axes of the laboratory, where the diffraction patterns were actually obtained, and the frame axes attached to the micelles.

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