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Full-Text Articles in Physics

Double Twist In Helical Polymer "Soft" Crystals, Christopher Y. Li, Stephen Z. D. Cheng, Jason J. Ge, Feng Bai, John Z. Zhang, Ian K. Mann, Frank W. Harris, Liang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz Nov 1999

Double Twist In Helical Polymer "Soft" Crystals, Christopher Y. Li, Stephen Z. D. Cheng, Jason J. Ge, Feng Bai, John Z. Zhang, Ian K. Mann, Frank W. Harris, Liang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz

Chemical Physics Publications

In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase, structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions, In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first ...


Helical Single-Lamellar Crystals Thermotropically Formed In A Synthetic Nonracemic Chiral Main-Chain Polyester, Christopher Y. Li, Donghang Yan, Stephen Z. D. Cheng, Feng Bai, Jason J. Ge, Bret H. Calhoun, Tianbai He, Liang-Chy Chien, Frank W. Harris, Bernard Lotz Nov 1999

Helical Single-Lamellar Crystals Thermotropically Formed In A Synthetic Nonracemic Chiral Main-Chain Polyester, Christopher Y. Li, Donghang Yan, Stephen Z. D. Cheng, Feng Bai, Jason J. Ge, Bret H. Calhoun, Tianbai He, Liang-Chy Chien, Frank W. Harris, Bernard Lotz

Chemical Physics Publications

Phase structures and transformation mechanisms of nonracemic chiral biological and synthetic polymers are fundamentally important topics in understanding their macroscopic responses in different environments. It has been known for many years that helical structures and morphologies can exist in low-ordered chiral liquid crystalline (LC) phases. However, when the chiral liquid crystals form highly ordered smectic liquid crystal phases, the helical morphology is suppressed due to the crystallization process. A double-twisted morphology has been observed in many liquid crystalline biopolymers such as dinoflaggellate chromosomes (in Prorocentrum micans) in an in vivo arrangement. Helical crystals grown from solution have been reported in ...


Electric-Field-Induced Chiral Separation In Liquid Crystals, G. Heppke, Antal Jákli, S. Rauch, Hans Sawade Nov 1999

Electric-Field-Induced Chiral Separation In Liquid Crystals, G. Heppke, Antal Jákli, S. Rauch, Hans Sawade

Chemical Physics Publications

Recently it was shown that smectic liquid crystal phases formed by achiral banana-shaped molecules are chiral: Films of such phases generally contain both homochiral (consisting of layers of the same chirality) and racemic (the chirality alternates in subsequent layers) domains. So far it has not been clear how to control the.. overall chirality of the sample;By observing the effects of the application of suitable electric fields, it was;;noted that chirality of a film of banana shaped molecules was interchanged between homochiral and racemic. We present dielectric, electro-optic, and polarization current measurements on both the racemic and chiral states ...


Dislocation Profile In Cholesteric Finger Texture, T. Ishikawa, Oleg Lavrentovich Nov 1999

Dislocation Profile In Cholesteric Finger Texture, T. Ishikawa, Oleg Lavrentovich

Chemical Physics Publications

The displacement field around an isolated elementary dislocation in a medium with one-dimensional periodicity is established experimentally. The system studied is a cholesteric fingerprint texture with a macroscopic (∼10 μm) periodicity. The characteristic elastic length is smaller than the “interlayer” distance. As a result, the experimental dislocation profile deviates from the classic pattern predicted by the linear elastic theory but fits well with the recently suggested nonlinear theory of dislocation [Phys. Rev. E 59, R4752 (1999)].


Light-Induced Director-Controlled Microassembly Of Dye Molecules From A Liquid Crystal Matrix, D. Voloschenko, Oleg Lavrentovich Nov 1999

Light-Induced Director-Controlled Microassembly Of Dye Molecules From A Liquid Crystal Matrix, D. Voloschenko, Oleg Lavrentovich

Chemical Physics Publications

We report on a light-induced phenomenon in dye-doped liquid crystals (LCs) with the distinctive features of molecular transport and assembly at micron scales. Under single-beam laser irradiation, the dye molecules phase separate from the LC host and assemble onto the cell substrate. Although the intensity of incident light is uniform within the irradiated area, the density of the adsorbed dye is modulated in accord with the director modulation of the LC. The dye molecules form a surface imprint that portrays orientational distortions of the LC host.


Nematic Polar Anchoring Strength Measured By Electric Field Techniques, Yuriy A. Nastishin, R. D. Polak, Sergij V. Shiyanovskii, V. H. Bodnar, Oleg Lavrentovich Oct 1999

Nematic Polar Anchoring Strength Measured By Electric Field Techniques, Yuriy A. Nastishin, R. D. Polak, Sergij V. Shiyanovskii, V. H. Bodnar, Oleg Lavrentovich

Chemical Physics Publications

We analyze the high-electric-field technique designed by Yokoyama and van Sprang [J. Appl. Phys. 57, 4520 (1985)] to determine the polar anchoring coefficient W of a nematic liquid crystal-solid substrate. The technique implies simultaneous measurement of the optical phase retardation and capacitance as functions of the applied voltage well above the threshold of the Frederiks transition. We develop a generalized model that allows for the determination of W for tilted director orientation. Furthermore, the model results in a new high-field technique, (referred to as the RV technique), based on the measurement of retardation versus applied voltage. W is determined from ...


Determination Of Nematic Polar Anchoring From Retardation Versus Voltage Measurements, Yu A. Natishin, R. D. Polak, Sergij V. Shiyanovskii, Oleg Lavrentovich Jul 1999

Determination Of Nematic Polar Anchoring From Retardation Versus Voltage Measurements, Yu A. Natishin, R. D. Polak, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

The popular “high-electric-field” technique to determine the polar anchoring coefficient W of a nematic–substrate interface requires the simultaneous measurement of the capacitance and optical phase retardation of a liquid crystal cell as a function of applied voltage. We develop a generalized model that makes it possible to eliminate the capacitance measurement. The new technique, called the RV (retardation versus voltage) technique, requires only themeasurement of retardation as a function of applied voltage, and allows for the determination ofW by a linear fit over a prescribed voltage window. The technique is not sensitive to uniformity of the cell thickness ...


Observation Of Pattern Evolution During Homeotropic-Focal Conic Transition In Cholesteric Liquid Crystals, Yang-Ming Zhu, Deng-Ke Yang Jun 1999

Observation Of Pattern Evolution During Homeotropic-Focal Conic Transition In Cholesteric Liquid Crystals, Yang-Ming Zhu, Deng-Ke Yang

Chemical Physics Publications

We have observed an interesting pattern evolution of cholesteric liquid crystals during the homeotropic-focal conic transition in a dispersed polymer network. From the electrical field induced homeotropic state, if the field is:reduced to an appropriate bias level focal conics grow at a constant speed, being an open or compact structure depending on the field strength. When the field is increased, these patterns change to ramified structures. We phenomenologically explained the observation.