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

Physics Commons

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

Kent State University

Discipline
Keyword
Publication Year
Publication
Publication Type

Articles 1 - 30 of 391

Full-Text Articles in Physics

Using The I-Motif As A Ph Sensor In Single-Molecule Fluorescence Microscopy Imaging, Jacob Taylor Apr 2018

Using The I-Motif As A Ph Sensor In Single-Molecule Fluorescence Microscopy Imaging, Jacob Taylor

Undergraduate Research Symposium

We used biophysics techniques to study the behavior of the single molecule human i-motif DNA structure as a function of the pH of its surroundings. We found that the molecule folds into a compact state around pH 6.0. We used FRET trace to observing the behavior of the molecule as it folds in a common imaging buffer of time-variant pH.


The Effects Of Light Scattering In Oled Efficiency, Andre Antoine, Bjorn Lussem Mar 2017

The Effects Of Light Scattering In Oled Efficiency, Andre Antoine, Bjorn Lussem

Undergraduate Research Symposium

OLED outcoupling efficiency is limited by several factors, one major factor is the limitation caused by internal reflection of light with the interface between organic layers including the anode and glass substrate. Here, we approach this problem by adding a fairly exotic material to the OLED setup, which strongly scatters light. We expect the scattering to weaken total internal reflection and increase outcoupling efficiency. Through measurements, we compare the out coupling efficiency of the control OLEDs and the OLEDs with the scattering layer. Finally, we analyze the potential for increased outcoupling efficiency and, later, industrial application. After analysis we find ...


Columnar Molecular Aggregation In The Aqueous Solutions Of Disodium Cromoglycate, Dena Mae Agra-Kooijman, Gautam Singh, Alexander Lorenz, Peter J. Collings, Heinz- S. Kitzerow, Satyendra Kumar Jun 2014

Columnar Molecular Aggregation In The Aqueous Solutions Of Disodium Cromoglycate, Dena Mae Agra-Kooijman, Gautam Singh, Alexander Lorenz, Peter J. Collings, Heinz- S. Kitzerow, Satyendra Kumar

Physics Publications

Stack, chimneylike, and threadlike assemblies have previously been proposed for the structure of disodium cromoglycate (DSCG) aggregates in aqueous solutions. The results of the synchrotron x-ray scattering investigations reported here reveal the formation of simple columnar assemblies with π-π stacking at a separation of 3.4 A between the DSCG molecules. Lateral separation between the assemblies is concentration ˚ and temperature dependent, varying from 35 to 42 A in the orientationally ordered nematic ( ˚ N) phase and from 27 to 32 A in the columnar or middle ( ˚ M) phase having long range lateral positional order. The assemblies’ length depends on concentration and ...


Origin Of Weak Layer Contraction In De Vries Smectic Liquid Crystals, Dena Mae Agra-Kooijman, Hyungguen Yoon, Sonal Dey, Satyendra Kumar Mar 2014

Origin Of Weak Layer Contraction In De Vries Smectic Liquid Crystals, Dena Mae Agra-Kooijman, Hyungguen Yoon, Sonal Dey, Satyendra Kumar

Physics Publications

Structural investigations of the de Vries smectic-A (SmA) and smectic-C (SmC) phases of four mesogens containing a trisiloxane end segment reveal a linear molecular conformation in the SmA phase and a bent conformation resembling a hockey stick in the SmC phase. The siloxane and the hydrocarbon parts of the molecule tilt at different angles relative to the smectic layer normal and are oriented along different directions. For the compounds investigated, the shape of orientational distribution function (ODF) is found to be sugarloaf shaped and not the widely expected volcano like with positive orientational order parameters: P2 = 0.53–0.78 ...


Advanced Materials, Kent State University - Kent Campus Jan 2014

Advanced Materials, Kent State University - Kent Campus

Researcher Directories, Division of Research and Sponsored Programs

20 page booklet highlighting researchers in Advanced Materials. This includes: Advanced Materials Applications, Advanced Materials Characterization, Biomaterials, Liquid Crystals


Bilayers In Nanoparticle-Doped Polar Mesogens, Alexander Lorenz, Dena Mae Agra-Kooijman, Natalie Zimmermann, Heinz-S. Kitzerow, Dean R. Evans Dec 2013

Bilayers In Nanoparticle-Doped Polar Mesogens, Alexander Lorenz, Dena Mae Agra-Kooijman, Natalie Zimmermann, Heinz-S. Kitzerow, Dean R. Evans

Physics Publications

Structures of the mesophases of five members of the 4-n-alkyl-4′-cyanobiphenyl homologous series (4-n-butyl-4′-cyanobiphenyl to 4-n-octyl-4′-cyanobiphenyl) doped with milled BaTiO3 nanoparticles were investigated by x-ray scattering. Clear solutions of each of the 4-n-alkyl-4′-cyanobiphenyls were first prepared in n-heptane and then doped with an n-heptane/nanoparticle dispersion, which led to gelation. The nanogels were found to be one-dimensional, multilayered, smectic nanostructures in each case. Surprisingly, a characteristic layer spacing of 4.5 nm was observed in all five homologues. Synchrotron x-ray scattering study of the multilayer structures of doped 4-n-pentyl-4′-cyanobiphenyl and 4-n-octyl-4′-cyanobiphenyl revealed nine orders ...


Partial-Wave Analysis Of Kn Scattering Reactions, Hongyu Zhang, John Tulpan, Manoj Shrestha, D. Mark Manley Sep 2013

Partial-Wave Analysis Of Kn Scattering Reactions, Hongyu Zhang, John Tulpan, Manoj Shrestha, D. Mark Manley

Physics Publications

We investigate the two-body reactions K¯¯¯N→K¯¯¯N, K¯¯¯N→πΛ, and K¯¯¯N→πΣ via single-energy partial-wave analyses in the center-of-mass (c.m.) energy range 1480 to 2100 MeV. The partial-wave amplitudes for these reactions thus extracted were constrained by a multichannel energy-dependent model satisfying unitarity of the partial-wave Smatrix. We obtain excellent predictions of differential cross sections, polarizations, polarized cross sections, and cross sections for these reactions from a global energy-dependent solution.


Multichannel Parametrization Of Antikaon-Nucleon Scattering Amplitudes And Extraction Of Resonance Parameters, Hongyu Zhang, John Tulpan, Manoj Shrestha, D. Mark Manley Sep 2013

Multichannel Parametrization Of Antikaon-Nucleon Scattering Amplitudes And Extraction Of Resonance Parameters, Hongyu Zhang, John Tulpan, Manoj Shrestha, D. Mark Manley

Physics Publications

We present results of a new multichannel partial-wave analysis for K¯¯¯N scattering in the center-of-mass (c.m.) energy range from 1480 to 2100 MeV. Resonance parameters were extracted by fitting partial-wave amplitudes from all considered channels using a multichannel parametrization that is consistent with S-matrix unitarity. The resonance parameters are generally in good agreement with predictions of the Koniuk-Isgur quark model.


Statistical Mechanics Of Bend Flexoelectricity And The Twist-Bend Phase In Bent-Core Liquid Crystals, Shaikh M. Shamid, Subas Dhakal, Jonathan V. Selinger May 2013

Statistical Mechanics Of Bend Flexoelectricity And The Twist-Bend Phase In Bent-Core Liquid Crystals, Shaikh M. Shamid, Subas Dhakal, Jonathan V. Selinger

Chemical Physics Publications

We develop a Landau theory for bend flexoelectricity in liquid crystals of bent-core molecules. In the nematic phase of the model, the bend flexoelectric coefficient increases as we reduce the temperature toward the nematic to polar phase transition. At this critical point, there is a second-order transition from high-temperature uniform nematic phase to low-temperature nonuniform polar phase composed of twist-bend or splay-bend deformations. To test the predictions of Landau theory, we perform Monte Carlo simulations to find the director and polarization configurations as functions of temperature, applied electric field, and interaction parameters.


Direct Piezoelectric Responses Of Soft Composite Fiber Mats, M. Varga, J. Morvan, Nicholas Diorio, E. Buyuktanir, John Harden, John L. West, Antal Jákli Apr 2013

Direct Piezoelectric Responses Of Soft Composite Fiber Mats, M. Varga, J. Morvan, Nicholas Diorio, E. Buyuktanir, John Harden, John L. West, Antal Jákli

Chemical Physics Publications

Recently soft fiber mats electrospun from solutions of Barium Titanate (BT) ferroelectric ceramics particles and polylactic acid (PLA) were found to have large (d(33) similar to 1 nm/V) converse piezoelectric signals offering a myriad of applications ranging from active implants to smart textiles. Here, we report direct piezoelectric measurements (electric signals due to mechanical stress) of the BT/PLA composite fiber mats at several BT concentrations. A homemade testing apparatus provided AC stresses in the 50 Hz-1.5 kHz-frequency range. The piezoelectric constant d(33) similar to 0.5 nC/N and the compression modulus Y similar to ...


Physical Limitations And Fundamental Factors Affecting Performance Of Liquid Crystal Tunable Lenses With Concentric Electrode Rings, Liewi Li, Doug Bryant, Tony Van Heugten, Philip Bos Mar 2013

Physical Limitations And Fundamental Factors Affecting Performance Of Liquid Crystal Tunable Lenses With Concentric Electrode Rings, Liewi Li, Doug Bryant, Tony Van Heugten, Philip Bos

Philip J. Bos

A comprehensive analysis of fundamental factors and their effects on the performance of liquid crystal (LC)-based lenses is given. The analysis adopts numerical LC director and electric field simulation, as well as scalar diffraction theory for calculating the lens performance considering different variable factors. A high-efficiency LC lens with concentric electrode rings is fabricated for verifying and enriching the analysis. The measurement results are in close agreement with the analysis, and a summary of key factors is given with their quantitative contributions to the efficiency.


Near-Diffraction-Limited Tunable Liquid Crystal Lens With Simplified Design, Liwei Li, Doug Bryant, Tony Van Heugten, Dwight Duston, Philip Bos Mar 2013

Near-Diffraction-Limited Tunable Liquid Crystal Lens With Simplified Design, Liwei Li, Doug Bryant, Tony Van Heugten, Dwight Duston, Philip Bos

Philip J. Bos

A high-efficiency tunable refractive lens based on liquid crystals with concentric electrode rings and a simple unique design of a resistor network is reported, and used to assess the performance of an optimized electrically tunable lens. It has a large number of phase control points to be able to accurately control the phase profile and produce high efficiency. The lens design uses resistors between neighboring electrodes to minimize external connections. The lens optical path difference is measured as a near perfect parabolic shape and the Strehl ratio of about 80% is obtained (comparing to a high-quality glass lens). Image evaluations ...


Characterization Of Cellular Uptake And Toxicity Of Aminosilane-Coated Iron Oxide Nanoparticles With Different Charges In Central Nervous System-Relevant Cell Culture Models, Zhizhi Sun, Vinith Yathindranath, Matthew Worden, James A. Thliveris, Stephanie Chu, Fiona E. Parkinson, Torsten Hegmann, Donald W. Miller Mar 2013

Characterization Of Cellular Uptake And Toxicity Of Aminosilane-Coated Iron Oxide Nanoparticles With Different Charges In Central Nervous System-Relevant Cell Culture Models, Zhizhi Sun, Vinith Yathindranath, Matthew Worden, James A. Thliveris, Stephanie Chu, Fiona E. Parkinson, Torsten Hegmann, Donald W. Miller

Chemical Physics Publications

Background: Aminosilane-coated iron oxide nanoparticles (AmS-IONPs) have been widely used in constructing complex and multifunctional drug delivery systems. However, the biocompatibility and uptake characteristics of AmS-IONPs in central nervous system (CNS)-relevant cells are unknown. The purpose of this study was to determine the effect of surface charge and magnetic field on toxicity and uptake of AmS-IONPs in CNS-relevant cell types.


Surface Induced Phase Separation And Pattern Formation At The Isotropic Interface In Chiral Nematic Liquid Crystals, Rafael S. Zola, L. R. Evangelista, Y.-C Yang, Deng-Ke Yang Jan 2013

Surface Induced Phase Separation And Pattern Formation At The Isotropic Interface In Chiral Nematic Liquid Crystals, Rafael S. Zola, L. R. Evangelista, Y.-C Yang, Deng-Ke Yang

Chemical Physics Publications

We study the pattern formation of a chiral nematic liquid crystal under a wetting transition. In the isotropic-liquid crystal transition, a surface-enhanced effect happens and a thin liquid crystal layer forms at the substrates of the cell. In this confined system, chirality, elastic anisotropy, surface anchoring, and wetting strength interplay. A striped pattern is formed due to the chiral nature of the material and the tilted anchoring at the isotropic boundary. As the wetting layer grows from cooling the sample, first the stripes rotate through a process where dislocation defects are formed. As the wetting layer grows further, the periodicity ...


Simulation Study Of Seemingly Fickian But Heterogeneous Dynamics Of Two Dimensional Colloids, Jeongmin Kim, Chanjoong Kim, Bong June Sung Jan 2013

Simulation Study Of Seemingly Fickian But Heterogeneous Dynamics Of Two Dimensional Colloids, Jeongmin Kim, Chanjoong Kim, Bong June Sung

Chemical Physics Publications

A two-dimensional (2D) solid lacks long-range positional order and is diffusive by means of the cooperative motion of particles. We find from molecular dynamics simulations of hard discs that 2D colloids in solid and hexatic phases show seemingly Fickian but strongly heterogeneous dynamics. Beyond translational relaxation time, the mean-square displacement is linear with time, t, implying that discs would undergo Brownian diffusion and the self-part of the van Hove correlation function [G(s)(r, t)] might be Gaussian. But dynamics is still heterogeneous and G(s)(r, t) is exponential at large r and oscillatory with multiple peaks at intermediate ...


New Particle Growth And Shrinkage Observed In Subtropical Environments, L. H. Young, Shan-Hu Lee, V. P. Kanawade, T-C. Hsiao, Y. L. Lee, B-F. Hwang, Y-J. Liou, H-T. Hsu, P-J. Tsai Jan 2013

New Particle Growth And Shrinkage Observed In Subtropical Environments, L. H. Young, Shan-Hu Lee, V. P. Kanawade, T-C. Hsiao, Y. L. Lee, B-F. Hwang, Y-J. Liou, H-T. Hsu, P-J. Tsai

Biostatistics, Environmental Health, and Epidemiology Publications

We present the first systematic analysis for new particle formation (NPF), growth and shrinkage of new particles at four different sites in subtropical central Taiwan. A total of 14 NPF events were identified from 137 days of ambient measurements during a cold and warm season. The measured formation rates of 10 nm particles (J10) and growth rates were in the range of 4.4–30 cm−3s−1 and 7.4–24 nm h−1, respectively. The onset of NPF events coincided with decreases of condensation sink (CS) and increases of SO2 under enhanced atmospheric mixing and ...


Comment On "The Limits Of Flexoelectricity In Liquid Crystals", Peter Palffy-Muhoray Jan 2013

Comment On "The Limits Of Flexoelectricity In Liquid Crystals", Peter Palffy-Muhoray

Chemical Physics Publications

In their paper, using the principle of energy conservation, F. Castles, S. M. Morris, and H. J. Coles [AIP Advances 1, 032120 (2011)] establish inequalities involving the elastic and dielectric constants and flexoelectric coefficients of liquid crystals. They then argue that recently measured values of flexoelectric coefficients by Harden et al. do not obey these inequalities, hence they violate the principle of energy conservation. In this comment, we point out that in their calculation, Castles et al. use an inappropriate value for an elastic constant, hence their conclusions, predicated on the outcome of this calculation, are not justified. Copyright 2013 ...


A Cellulose Liquid Crystal Motor: A Steam Engine Of The Second Kind, Yong Geng, Pedro Lucio Almeida, Cheng Cheng, Peter Palffy-Muhoray, Maria Helena Godinho, Susete Nogueira Fernandes Jan 2013

A Cellulose Liquid Crystal Motor: A Steam Engine Of The Second Kind, Yong Geng, Pedro Lucio Almeida, Cheng Cheng, Peter Palffy-Muhoray, Maria Helena Godinho, Susete Nogueira Fernandes

Chemical Physics Publications

The salient feature of liquid crystal elastomers and networks is strong coupling between orientational order and mechanical strain. Orientational order can be changed by a wide variety of stimuli, including the presence of moisture. Changes in the orientation of constituents give rise to stresses and strains, which result in changes in sample shape. We have utilized this effect to build soft cellulose-based motor driven by humidity. The motor consists of a circular loop of cellulose film, which passes over two wheels. When humid air is present near one of the wheels on one side of the film, with drier air ...


Designing Dupin Cyclides In Micro And Macro Worlds, Oleg Lavrentovich Jan 2013

Designing Dupin Cyclides In Micro And Macro Worlds, Oleg Lavrentovich

Oleg Lavrentovich

No abstract provided.


X-Ray Scattering Of A Nematic Liquid Crystal Nano-Dispersion With Negative Dielectric Anisotropy, A. Lorenz, N. Zimmermann, Satyendra Kumar, S. R. Evans, G. Cook, M. F. Martinez, H. S. Kitzerow Jan 2013

X-Ray Scattering Of A Nematic Liquid Crystal Nano-Dispersion With Negative Dielectric Anisotropy, A. Lorenz, N. Zimmermann, Satyendra Kumar, S. R. Evans, G. Cook, M. F. Martinez, H. S. Kitzerow

Physics Publications

A nematic liquid crystal (LC) mixture was doped with harvested ferroelectric BaTiO3 nanoparticles and investigated with wide- and small-angle x-ray scattering upon heating from the nematic to the isotropic phase. At moderate temperatures, colloidal crystallites were observed. LC test cells with homeotropic anchoring were placed in the x-ray beam and the realignment of the LC director was investigated upon applying an electric field.


Soft Elasticity In Main Chain Liquid Crystal Elastomers, S. Dey, D. M. Agra-Kooijman, W. Ren, P. J. Mcmullan, A. C. Griffin, Satyendra Kumar Jan 2013

Soft Elasticity In Main Chain Liquid Crystal Elastomers, S. Dey, D. M. Agra-Kooijman, W. Ren, P. J. Mcmullan, A. C. Griffin, Satyendra Kumar

Physics Publications

Main chain liquid crystal elastomers exhibit several interesting phenomena, such as three different regimes of elastic response, unconventional stress-strain relationship in one of these regimes, and the shape memory effect. Investigations are beginning to reveal relationships between their macroscopic behavior and the nature of domain structure, microscopic smectic phase structure, relaxation mechanism, and sample history. These aspects of liquid crystal elastomers are briefly reviewed followed by a summary of the results of recent elastic and high-resolution X-ray diffraction studies of the shape memory effect and the dynamics of the formation of the smectic-C chevron-like layer structure. A possible route to ...


Spatial And Orientational Control Of Liquid Crystal Alignment Using A Surface Localized Polymer Layer, Lu Lu, Tatiana Sergan, Vassili Sergan, Philip J. Bos Dec 2012

Spatial And Orientational Control Of Liquid Crystal Alignment Using A Surface Localized Polymer Layer, Lu Lu, Tatiana Sergan, Vassili Sergan, Philip J. Bos

Chemical Physics Publications

We present an alignment method for the surface contacting liquid crystal (LC) director. This method allows complete control of the polar pretilt angle as a function of position in a liquid crystal device, and has the potential of controlling the azimuthal orientation of LC. Important considerations of this method are to form a thin layer of reactive monomers at the LC cell interior surface, and to control the deleterious effects of flow due to polymerization induced concentration gradients. To achieve these, the voltage and frequency of the applied electric field and the UV intensity during the polymerization process are significant.


Mechanism Of Electric-Field-Induced Segregation Of Additives In A Liquid-Crystal Host, Lu Lu, Vassili Sergan, Philip J. Bos Nov 2012

Mechanism Of Electric-Field-Induced Segregation Of Additives In A Liquid-Crystal Host, Lu Lu, Vassili Sergan, Philip J. Bos

Chemical Physics Publications

The mechanism for electric-field-induced segregation of additives, containing a polar group, in a host liquid crystal is proposed. It is shown that the polarity of an applied dc electric field, or the frequency of an ac electric field, strongly influences the segregation of reactive monomers containing an ester group. An explanation of this result is offered based on the association of dissolved ions with polar groups of the reactive monomers. This association is considered to cause these types of additives to drift to the cell surface in the presence of an external electric field. The described mechanism can be applied ...


Doping The Nematic Liquid Crystal 5cb With Milled Batio3 Nanoparticles, Alexander Lorenz, Natalie Zimmerman, Satyendra Kumar, Dean R. Evans, Gary Cook, Hienz-S. Kitzerow Nov 2012

Doping The Nematic Liquid Crystal 5cb With Milled Batio3 Nanoparticles, Alexander Lorenz, Natalie Zimmerman, Satyendra Kumar, Dean R. Evans, Gary Cook, Hienz-S. Kitzerow

Physics Publications

The simple nematic mesogen 5CB was doped with milled BaTiO3 nanoparticles and was investigated with x-ray scattering. Doping with BaTiO3 nanoparticles of 9 nm in diameter led to the formation of crystallites. These crystallites precipitated and formed a waxlike nanodispersion of 5CB and nanoparticles, which led to intense x-ray scattering signals characteristic of a multilayer structure. Surprisingly, the multilayers possess unusual interlayer spacing, which cannot be explained by simple smectic order of the calamitic molecules.


Multichannel Parametrization Of Pi N Scattering Amplitudes And Extraction Of Resonance Parameters, Manoj Shrestha, D. Mark Manley Nov 2012

Multichannel Parametrization Of Pi N Scattering Amplitudes And Extraction Of Resonance Parameters, Manoj Shrestha, D. Mark Manley

Physics Publications

We present results of a new multichannel partial-wave analysis for πN scattering in the c.m. energy range 1080 to 2100 MeV. This work explicitly includes ηN and KΛ channels and the single pion photoproduction channel. Resonance parameters were extracted by fitting partial-wave amplitudes from all considered channels using a multichannel parametrization that is consistent with S-matrix unitarity. The resonance parameters so obtained are compared to predictions of quark models.


Polar Bent-Shape Liquid Crystals - From Molecular Bend To Layer Splay And Chirality, Antal Jakli, A. Eremin Oct 2012

Polar Bent-Shape Liquid Crystals - From Molecular Bend To Layer Splay And Chirality, Antal Jakli, A. Eremin

Antal Jakli

Considerable progress has been achieved in understanding the fascinating structure and physical properties of the ferroelectric liquid crystalline phases formed by bent-core liquid crystals (BLC). In this review, we discuss a manifold of polar structures and phases found in BLCs such as orthogonal and tilted ferro-/antiferroelectric phases, smectic phases, switchable columnar phases, modulated structures and phases stabilised by a periodic lattice of defects such as dark conglomerate and nanofilament phases. We review the theoretical aspects of ferroelectricity in BLCs including existing microscopic theories and computer simulations, polarity and chirality phenomena. The last part of the paper is devoted to ...


Partial-Wave Analysis Of The Pi- + Proton Goes To Eta Meson + Neutron And Pi- + Proton Goes To Neutral Kaon + Lambda Reactions, Manoj Shrestha, D. Mark Manley Oct 2012

Partial-Wave Analysis Of The Pi- + Proton Goes To Eta Meson + Neutron And Pi- + Proton Goes To Neutral Kaon + Lambda Reactions, Manoj Shrestha, D. Mark Manley

Physics Publications

We investigate the hadronic reactions πN→ηN and πN→KΛ via single-energy partial-wave analyses in the c.m. energy range 1080 to 2100 MeV. Our results for the KΛ channel are consistent with prior works; however, for the ηNchannel our results differ significantly from previous energy-dependent partial-wave analyses that violate the S-matrix unitarity. We present results of ηN and KΛ partial-wave amplitudes constrained by a unitary energy-dependent model. We obtain excellent predictions of integrated cross sections for the two reactions from a global energy-dependent solution. Our results imply that the region just above S11(1535) has a major contribution from ...


Deformation Of An Asymmetric Thin Film, Jun Geng, Jonathan V. Selinger Sep 2012

Deformation Of An Asymmetric Thin Film, Jun Geng, Jonathan V. Selinger

Chemical Physics Publications

Experiments have investigated shape changes of polymer films induced by asymmetric swelling by a chemical vapor. Inspired by recent work on the shaping of elastic sheets by non-Euclidean metrics [ Y. Klein, E. Efrati and E. Sharon Science 315 1116 (2007)], we represent the effect of chemical vapors by a change in the target metric tensor. In this problem, unlike that earlier work, the target metric is asymmetric between the two sides of the film. Changing this metric induces a curvature of the film, which may curve into a partial cylinder or a partial sphere. We calculate the elastic energy for ...


Direct Observation Of Smectic Layers In Thermotropic Liquid Crystals, C. Zhang, M. Gao, Wolfgang Weissflog, Ute Baumeister, Samuel N. Sprunt, Jim T. Gleeson, Antal Jákli Sep 2012

Direct Observation Of Smectic Layers In Thermotropic Liquid Crystals, C. Zhang, M. Gao, Wolfgang Weissflog, Ute Baumeister, Samuel N. Sprunt, Jim T. Gleeson, Antal Jákli

Chemical Physics Publications

We demonstrate subnanometer resolution cryo-TEM imaging of smectic layers in the smectic and nematic phases of two bent-core liquid crystals. Our results show perfect periodicity over several hundred layers in the smectic phase and also provide the first direct evidence of smectic clusters on length scales of 30-50 nm in a nematic liquid crystal. The results are corroborated with small angle x-ray scattering measurements. The observation of smectic clusters in the nematic phase is of special interest in bent-core liquid crystals, where the smectic clusters are stable over wide temperature ranges, in contrast to the well-known pretransitional "cybotactic" clusters that ...


Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson Aug 2012

Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson

Chemical Physics Publications

We report on a series of measurements on the microscopic structure and the magneto-optical properties of a calamitic liquid crystalline compound in its nematic phase. Structural studies show the existence of short-range, tilted smectic order consistent with pretransitional effects above an underlying smectic phase. Concomitantly, magneto-optical results exhibit the existence of an optic axis not collinear with the uniaxial director. This apparent biaxial nature is discussed within the context of coupling between the tensor nematic and the smectic order parameters.