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Articles 1 - 10 of 10

Full-Text Articles in Physics

Morphology And Ordering In Thin Liquid-Crystal Films On Flat Glass Substrates, Yushan Shi, Brian Cull, Satyendra Kumar Oct 1993

Morphology And Ordering In Thin Liquid-Crystal Films On Flat Glass Substrates, Yushan Shi, Brian Cull, Satyendra Kumar

Physics Publications

Results of a high resolution x-ray reflectivity study of growth morphology and ordering of thin liquid-crystal films on flat glass substrate are reported. An adsorbed bilayer of crystalline order, under three dimensional clusters, was found to persist well beyond the nematic to isotropic transition. This adsorbed layer appears to be related to the surface memory effects in liquid-crystal devices. The morphology of these films can be described by the Stranski-Krastanov growth mode.


Cholesteric Polymer-Dispersed Light Shutters, John L. West, R. B. Akins, J. Francl, J. W. Doane Sep 1993

Cholesteric Polymer-Dispersed Light Shutters, John L. West, R. B. Akins, J. Francl, J. W. Doane

Chemistry & Biochemistry Publications

We report cholesteric/polymer dispersed (CPD) materials that switch from a reflecting, planar state to a relatively transparent, focal conic state. The reflective wavelength of the CPD materials can be continuously adjusted by varying the cholesteric pitch length. The electro‐optic properties of these materials are similar to the recently reported polymer stabilized cholesteric materials; however, the polymer concentration is sufficient to provide a self‐sustaining and self‐adhering film, offering the potential of large area devices fabricated on flexible substrates.


Theory Of A Symmetry-Breaking Phase-Transition In A Surface-Layer Of Nematic Liquid-Crystal, Y. L'Vov, R. M. Hornreich, David W. Allender Aug 1993

Theory Of A Symmetry-Breaking Phase-Transition In A Surface-Layer Of Nematic Liquid-Crystal, Y. L'Vov, R. M. Hornreich, David W. Allender

Physics Publications

For a surface interaction linear in the order parameter and favoring an orientation in which liquid-crystalline molecules lie parallel to the surface (but which is independent of whether the orientation is uniaxial or isotropic in the bounding plane), a symmetry-breaking phase transition in a surface layer is possible at temperatures above that of the bulk isotropic to nematic transition. At the surface transition, the high-temperature in-plane isotropic state becomes unstable with respect to a biaxial phase, the transition being continuous and therefore of-the Berezinskii-Kosterlitz-Thouless (BKT) type, It is expected to occur for intermediate surface couplings but not at very weak ...


Correct Phase-Diagrams Of Liquid-Crystals Reported To Exhibit The (Nonexistent) Incommensurate Smectic-A Phases, P. Patel, Satyendra Kumar Jul 1993

Correct Phase-Diagrams Of Liquid-Crystals Reported To Exhibit The (Nonexistent) Incommensurate Smectic-A Phases, P. Patel, Satyendra Kumar

Physics Publications

Three different incommensurate phases predicted by the phenomenological theory of frustrated smectics were reportedly found in mixtures of DB8OCN and 8OBCAB and DB7OCN and 8OCB. The results of our high-resolution X-ray diffraction study of these materials show that these phases are, indeed, coexistences of two or more smectic-A phases. The correct phase diagrams of the two systems are found to be in excellent agreement with the phenomenological models. At this time, there remain no known materials that exhibit an incommensurate smectic-A phase.


Molecular-Motion Analysis Of 5cb In Pdlcs Using Solid-State C-13 Nmr Relaxation Spectroscopy, Karen L. Buchert, Jack L. Koenig, Shi-Qing Wang, John L. West Jul 1993

Molecular-Motion Analysis Of 5cb In Pdlcs Using Solid-State C-13 Nmr Relaxation Spectroscopy, Karen L. Buchert, Jack L. Koenig, Shi-Qing Wang, John L. West

Chemistry & Biochemistry Publications

In samples of polymer-dispersed liquid crystals (PDLCs), submicron droplets of liquid crystal reside within a polymer matrix. By the use of the cross polarization technique for solid-state C-13 NMR spectroscopy, the NMR spectrum of the liquid crystal can be obtained without interference from the polymer spectrum, even though the two materials have some similar chemical structures. Both C-13 T1 and C-13 T1 rho relaxation experiments were performed on a PDLC system of 5CB in epoxy as a function of 5CB domain size. The C-13 T1 relaxation constants and the localized motions they measure showed no significant change over the liquid ...


Field-Driven 1st-Order Structural Transition In The Restricted Geometry Of A Smectic-A Cell, Oleg Lavrentovich, M. Kléman Jul 1993

Field-Driven 1st-Order Structural Transition In The Restricted Geometry Of A Smectic-A Cell, Oleg Lavrentovich, M. Kléman

Chemical Physics Publications

An external field gives rise to a first-order transition in a smectic-A cell; the transition occurs by nucleation of focal conic domains. The physical mechanisms that govern the behavior of the new domain phase are different for small (ρ≪1) and large (ρ≫1) values of the order parameters ρ [ρ=(domain radius)/(cell thickness)]. The nucleation (ρ≪1) is governed by the elastic and field energies and is facilitated by bulk or surface irregularities, while the expansion (ρ≫1) is determined by the balance of the field and anisotropic surface energy.


Phase-Diagram Of A Frustrated Smectic Liquid-Crystal System And The Absence Of The Incommensurate Smectic-A(I2) Phase, Prem Patel, Li Chen, Satyendra Kumar Apr 1993

Phase-Diagram Of A Frustrated Smectic Liquid-Crystal System And The Absence Of The Incommensurate Smectic-A(I2) Phase, Prem Patel, Li Chen, Satyendra Kumar

Physics Publications

The phase diagram and the structure of smectic-A(d) (Sm-A(d)) and Sm-A2 phases of binary mixtures of 4-octyloxy-4'-cyanobiphenyl (8OCB) and 4-n-heptyloxyphenyl-4'-cyanobenzoyloxybenzoate (DB7OCN) have been determined by high-resolution x-ray diffraction. This system had previously been reported by Ratna, Shashidhar, and Raja [Phys. Rev. Lett. 55, 1476 (1985)] to exhibit an incommensurate Sm-A(i2) phase for concentrations of 8OCB ranging from 25 to 40 mol %. The phase diagram obtained from the present study is in excellent agreement with the mean-field theory of Prost and co-workers [J. Phys. (Paris) 46, 391 (1985)]. The results of the x-ray study establish that ...


Phase Diagram Of A Frustrated Smectic Liquid-Crystal System And The Absence Of The Incommensurate Smectic-AI2 Phase, Prem Patel, Li Chen, Satyendra Kumar Apr 1993

Phase Diagram Of A Frustrated Smectic Liquid-Crystal System And The Absence Of The Incommensurate Smectic-AI2 Phase, Prem Patel, Li Chen, Satyendra Kumar

Physics Publications

The phase diagram and the structure of smectic-Ad (Sm-Ad) and Sm-A2 phases of binary mixtures of 4-octyloxy-4’-cyanobiphenyl (8OCB) and 4-n-heptyloxyphenyl-4’-cyanobenzoyloxybenzoate (DB7OCN) have been determined by high-resolution x-ray diffraction. This system had previously been reported by Ratna, Shashidhar, and Raja [Phys. Rev. Lett. 55, 1476 (1985)] to exhibit an incommensurate Sm-Ai2phase for concentrations of 8OCB ranging from 25 to 40 mol %. The phase diagram obtained from the present study is in excellent agreement with the mean-field theory of Prost and co-workers [J. Phys. (Paris) 46, 391 (1985 ...


Analysis Of Polymer-Dispersed Liquid Crystals By Infrared Spectroscopy, Coleen A. Mcfarland, Jack L. Koenig, John L. West Mar 1993

Analysis Of Polymer-Dispersed Liquid Crystals By Infrared Spectroscopy, Coleen A. Mcfarland, Jack L. Koenig, John L. West

Chemistry & Biochemistry Publications

FT-IR microspectroscopy is used to compare the polymer and liquid crystal droplet regions within polymer-dispersed liquid crystal (PDLC) films. Thermoplastic polymer matrix PDLCs contain a higher amount of liquid crystal within the polymer regions than do thermoset polymer matrix films. IR functional group images of a droplet show characteristic textures corresponding to the visual images of the same droplet. The textures in the IR images change with IR polarization and with an applied electric field. Analysis by conventional IR spectroscopy shows that the C=N and the pentyl CH2 groups require an equivalent voltage to switch in the IR ...


Molecular-Motion Analysis Of E7 In Pdlcs As A Function Of Droplet Size Using Solid-State C-13 Nmr Relaxation Spectroscopy, Karen L. Buchert, Jack L. Koenig, Shi-Qing Wang, John L. West Jan 1993

Molecular-Motion Analysis Of E7 In Pdlcs As A Function Of Droplet Size Using Solid-State C-13 Nmr Relaxation Spectroscopy, Karen L. Buchert, Jack L. Koenig, Shi-Qing Wang, John L. West

Chemistry & Biochemistry Publications

13C NMR relaxation spectroscopy as applied to polymer-dispersed liquid crystals (PDLCs) provides a method for measuring the molecular motions of the liquid crystal molecules within droplets dispersed throughout the material's polymer matrix. Because liquid crystal molecular motion may play a major role in the switching phenomenon of PDLC materials from an opaque film to a clear film, both T 1 and T 1ρ relaxation experiments are used to measure molecular mobility of the liquid crystal as a function of droplet size for PDLC materials made of E7 and epoxy. The segmental molecular motions measured by T 1 ...