Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 8 of 8

Full-Text Articles in Physics

Dielectric Properties Of Mixtures Of A Bent-Core And A Calamitic Liquid Crystal, Peter Salamon, Nandor Éber, Agnes Buka, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli Mar 2010

Dielectric Properties Of Mixtures Of A Bent-Core And A Calamitic Liquid Crystal, Peter Salamon, Nandor Éber, Agnes Buka, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli

Chemical Physics Publications

Dielectric spectroscopy measurements have been performed on a bent-core nematic liquid crystal and on its binary mixtures with a calamitic nematic. We have detected more dispersions in the bent-core compound than in the calamitic one, including one at an unusually low frequency of a few kilohertz. The dispersions detected in the mixtures have been identified and the spectra have been split into contributions of the constituents. In order to connect the dielectric increment with the molecular dipole moment we have applied a sophisticated conformational calculation not performed before for a large, flexible mesogen molecule with numerous polar groups.


Effects Of Dielectric Relaxation On The Director Dynamics Of Uniaxial Nematic Liquid Crystals, Mingxia Gu, Ye Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich Dec 2007

Effects Of Dielectric Relaxation On The Director Dynamics Of Uniaxial Nematic Liquid Crystals, Mingxia Gu, Ye Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

The dielectric anisotropy of liquid crystals causes director reorientation in an applied electric field and is thus at the heart of electro-optic applications of these materials. The components of the dielectric tensor are frequency dependent. Until recently, this frequency dependence was not accounted for in a description of director dynamics in an electric field. We theoretically derive the reorienting dielectric torque acting on the director, taking into account the entire frequency spectrum of the dielectric tensor. The model allows one to include the effects of multiple relaxations in both parallel and perpendicular components of the dielectric tensor, thus generalizing a ...


Pretransitional Fluctuations In The Isotropic Phase Of A Lyotropic Chromonic Liquid Crystal, Yuriy A. Nastishin, Sergij V. Shiyanovskii, Oleg Lavrentovich, A. F. Kostko, M. A. Anisimov Nov 2004

Pretransitional Fluctuations In The Isotropic Phase Of A Lyotropic Chromonic Liquid Crystal, Yuriy A. Nastishin, Sergij V. Shiyanovskii, Oleg Lavrentovich, A. F. Kostko, M. A. Anisimov

Chemical Physics Publications

We have studied isotropic-to-nematic pretransitional fluctuations in an aqueous solution of disodium cromoglycate (cromolyn) by static and dynamic light scattering. Cromolyn is a representative of lyotropic chromonic liquid crystals with building units being elongated rods formed by aggregates of disk-like molecules. By combining light-scattering and viscosity measurements we have determined the correlation length and relaxation time of the orientational order-parameter fluctuations and estimated the size of the cromolyn aggregates. The pretransitional behavior of light scattering does not completely follow the classic Landau-de Gennes model. This feature is most probably associated with the variable length of cromolyn aggregates. We have observed ...


Dielectric Relaxation Behavior Of A Liquid Crystal Showing An Unusual Type Of Antiferroelectric-Ferroelectric-Antiferroelectric Phase Sequence, S. K. Kundu, B. K. Chaudhuri, A. Seed, Antal Jakli Apr 2003

Dielectric Relaxation Behavior Of A Liquid Crystal Showing An Unusual Type Of Antiferroelectric-Ferroelectric-Antiferroelectric Phase Sequence, S. K. Kundu, B. K. Chaudhuri, A. Seed, Antal Jakli

Chemical Physics Publications

The temperature and frequency dependent dielectric relaxation behavior of a liquid crystalline (S)-(+)-1-methylheptyl 4-[2-(4-alkoxyphenyl) thiophene-5-carbonylthiooxy] benzoate system is reported. Interesting successive antiferroelectric-ferroelectric-antiferroelectric (AF-FE-AF) phase transitions are observed in this system resembling the successive phase transitions observed in crystalline Rochelle salt. The smectic-C*(SmC*) to AF1 phase transition (around 103.0 °C) is first order in nature, predicted from the use of Orihara and Ishibashi theory. It is also found that a contribution of the ferroelectric SmC* phase ordering penetrates even in the antiferroelectric AF1 (SmCA*) and AF2 (SmCA*) phases very ...


Fourier Transform Infrared Imaging Of Nematic Liquid Crystals, Denise Wade Rafferty, Jack L. Koenig, Gregory Magyar, John L. West Mar 2002

Fourier Transform Infrared Imaging Of Nematic Liquid Crystals, Denise Wade Rafferty, Jack L. Koenig, Gregory Magyar, John L. West

Chemistry & Biochemistry Publications

Fourier transform infrared spectroscopy is often used to study, liquid crystals and liquid crystal systems. In this work, the factors that influence the IR absorbance of nematic liquid crystals and their consequences on FT-IR imaging are examined. In the IR spectrum of E7, ordering in the nematic phase causes a 28.7% reduction in the nitrile band height relative to the isotropic phase, and the combination of ordering and liquid crystal director alignment causes a 65.0% decrease in the nitrile band height. For a phase-separated blend of E7 and 10% NOA65 polymer, the FT-IR images were found to be ...


Ft-Ir Imaging Of Patterned Photocrosslinkable Poly(Vinyl Cinnamate), Denise Wade Rafferty, Jack L. Koenig, Gregory Magyar, John L. West Jan 2002

Ft-Ir Imaging Of Patterned Photocrosslinkable Poly(Vinyl Cinnamate), Denise Wade Rafferty, Jack L. Koenig, Gregory Magyar, John L. West

Chemistry & Biochemistry Publications

The use of photocrosslinkable polymers and photomasks was proposed as a means of reducing the number of raw materials necessary to create a chemical sensor array. To test this hypothesis, poly(vinyl cinnamate) was crosslinked to various degrees with the use of a photomask, exposed to a binary solvent vapor of benzonitrile and dimethyl formamide, and examined by FT-IR imaging. The results illustrate that FT-IR imaging is effective for visualizing the patterning of the crosslink density of a polymer film as well as the temporal and spatial sorption patterns of different solvent vapors. The FT-IR images show that the decrease ...


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 ...


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 ...