scholarly journals Nematic Liquid Crystal Composite Materials for DC and RF Switching

Technologies ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 32 ◽  
Author(s):  
Mohiuddin Munna ◽  
Farhana Anwar ◽  
Ronald Coutu
Keyword(s):  
Electrical Conductivity ◽  
Liquid Crystal ◽  
Carbon Nanotube ◽  
Composite Materials ◽  
Liquid Crystals ◽  
Local Heating ◽  
Device Fabrication ◽  
Pure Liquid ◽  
Dual Frequency ◽  
Concentration Effects

Liquid Crystals (LCs) are widely used in display devices, electro-optic modulators, and optical switches. A field-induced electrical conductivity modulation in pure liquid crystals is very low which makes it less preferable for direct current (DC) and radio-frequency (RF) switching applications. According to the literature, a conductivity enhancement is possible by nanoparticle doping. Considering this aspect, we reviewed published works focused on an electric field-induced conductivity modulation in carbon nanotube-doped liquid crystal composites (LC-CNT composites). A two to four order of magnitude switching in electrical conductivity is observed by several groups. Both in-plane and out-of-plane device configurations are used. In plane configurations are preferable for micro-device fabrication. In this review article, we discussed published works reporting the elastic and molecular interaction of a carbon nanotube (CNT) with LC molecules, temperature and CNT concentration effects on electrical conductivity, local heating, and phase transition behavior during switching. Reversibility and switching speed are the two most important performance parameters of a switching device. It was found that dual frequency nematic liquid crystals (DFNLC) show a faster switching with a good reversibility, but the switching ratio is only two order of magnitudes. A better way to ensure reversibility with a large switching magnitude is to use two pairs of in-plane electrodes in a cross configuration. For completeness and comparison purposes, we briefly reviewed other nanoparticle- (i.e., Au and Ag) doped LC composite’s conductivity behavior as well. Finally, based on the reported works reviewed in this article on field induced conductivity modulation, we proposed a novel idea of RF switching by LC composite materials. To support the idea, we simulated an LC composite-based RF device considering a simple analytical model. Our RF analysis suggests that a device made with an LC-CNT composite could show an acceptable performance. Several technological challenges needed to be addressed for a physical realization and are also discussed briefly.

Dual frequency conductivity switching in a carbon nanotube/liquid crystal composite

Carbon ◽  
2013 ◽  
Vol 59 ◽  
pp. 512-517 ◽  
Author(s):  
S. Krishna Prasad ◽  
M. Vijay Kumar ◽  
C.V. Yelamaggad
Keyword(s):  
Liquid Crystal ◽  
Carbon Nanotube ◽  
Dual Frequency ◽  
Conductivity Switching ◽  
Crystal Composite

scholarly journals Overlooked Ionic Phenomena Affecting the Electrical Conductivity of Liquid Crystals

2021 ◽  
Vol 11 (1) ◽  
pp. 1
Author(s):  
David Webb ◽  
Yuriy Garbovskiy
Keyword(s):  
Electrical Conductivity ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Physical Properties ◽  
Soft Matter ◽  
Photonic Devices ◽  
Optical Components ◽  
Dynamically Reconfigurable ◽  
Liquid Crystal Devices ◽  
New Applications

Liquid crystal devices, such as displays, various tunable optical components, and sensors, are becoming increasingly ubiquitous. Basic physical properties of liquid crystal materials can be controlled by external physical fields, thus making liquid crystal devices dynamically reconfigurable. The tunability of liquid crystals offers exciting opportunities for the development of new applications, including advanced electronic and photonic devices, by merging the concepts of flat optics, tunable metasurfaces, nanoplasmonics, and soft matter biophotonics. As a rule, the tunability of liquid crystals is achieved by applying an electric field. This field reorients liquid crystals and changes their physical properties. Ions, typically present in liquid crystals in minute quantities, can alter the reorientation of liquid crystals through the well-known screening effect. Because the electrical conductivity of thermotropic liquid crystals is normally caused by ions, an understanding of ion generation processes in liquid crystals is of utmost importance to existing and emerging technologies relying on such materials. That is why measuring of electrical conductivity of liquid crystals is a standard part of their material characterization. Measuring the electrical conductivity of liquid crystals is a very delicate process. In this paper, we discuss overlooked ionic phenomena caused by interactions of ions with substrates of the liquid crystal cells. These interactions affect the measured values of the DC electrical conductivity of liquid crystals and make them dependent on the cell thickness.

Electric-Field Effects in Dilute Suspensions of Carbon Nanotubes Dispersed in Nematic Liquid Crystals

2010 ◽  
Vol 428-429 ◽  
pp. 173-181 ◽  
Author(s):  
Muklesur Rahman ◽  
Wei Lee
Keyword(s):  
Carbon Nanotubes ◽  
Liquid Crystal ◽  
Carbon Nanotube ◽  
Liquid Crystals ◽  
Liquid Crystalline ◽  
Colloidal Particles ◽  
Liquid Crystal Display ◽  
New Physics ◽  
Colloidal System ◽  
Colloidal Systems

Colloids composed of liquid-crystal hydrosols exhibit a rich set of interesting phenomena. The coupling between liquid-crystalline media and colloidal particles plays an essential role leading to an abundant source of new physics. In the last few years, peculiar behaviors of carbon-nanotube-doped calamitic liquid crystals have attracted considerable attention. This paper provides a brief introduction to this alluring subject for its on-going research development in this laboratory. First presented are our current understandings of the nematic colloidal system comprising carbon nanotubes and of their possible orientation and dynamics under the application of an external field. Various electro-optical and electrical properties of a liquid-crystal display rectified by the nanoscale carbonaceous guest are then addressed to a larger extent. Dielectric relaxation obtained from a nematic impregnated with carbon nanotubes is also discussed. With historical significance for the dawn of the liquid-crystal–carbon-nanotube research, several important findings of enhanced nonlinear optical properties in typical nematic mesomaterials consisting of suspended nanotubes are delineated. With the new colloidal systems of elongated nanoscale solids dispersed in anisotropic fluids in the mesophase, many new intriguing phenomena are awaiting theoretical and experimental explorations. Collaborations are called to draw attention of interested theoretical physicists, in particular.

Ordered Micro-Particle Structures in a Liquid Crystal: Formation and Physical Properties

2004 ◽  
Vol 817 ◽  
Author(s):  
Ke Zhang ◽  
Anatoliy Glushchenko ◽  
John L. West
Keyword(s):  
Mechanical Properties ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Shear Rate ◽  
Electric Fields ◽  
Published Data ◽  
Pure Liquid ◽  
Crystal Formation ◽  
Complex Structures ◽  
High Electric Fields

AbstractOrdered colloids are of great scientific and practical interests. Liquid crystals offer enhanced ways of producing and stabilizing these complex structures. We therefore studied the rheological and electro-rheological properties of the structured colloids as a means of probing this stabilization. We found that the mechanical properties of the colloids and stability of their 3D structures can be controlled by the particles size and distribution. In addition, when an electric field is applied, we observed an increase in the apparent viscosity with saturation at high electric fields. This effect depends on the shear rate and temperature. The results are also compared with the published data for the viscosity measurements of pure liquid crystals and isotropic colloids. While we are only beginning to understand the details of these complex colloids we expect they will find a wide variety of applications.

scholarly journals Electro-Optical Switching of Dual-Frequency Nematic Liquid Crystals: Regimes of Thin and Thick Cells

Crystals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 314 ◽  
Author(s):  
Olha Melnyk ◽  
Yuriy Garbovskiy ◽  
Dario Bueno-Baques ◽  
Anatoliy Glushchenko
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Optical Switching ◽  
Nematic Liquid Crystals ◽  
Optical Response ◽  
Thin Layers ◽  
Optical Performance ◽  
Dual Frequency ◽  
Crystal Cells ◽  
Cell Thickness

Conventional display applications of liquid crystals utilize thin layers of mesogenic materials, typically less than 10 µm. However, emerging non-display applications will require thicker, i.e., greater than 100 µm, layers of liquid crystals. Although electro-optical performance of relatively thin liquid crystal cells is well-documented, little is known about the properties of thicker liquid crystal layers. In this paper, the electro-optical response of dual-frequency nematic liquid crystals is studied using a broad range (2–200 µm) of the cell thickness. Two regimes of electro-optical switching of dual-frequency nematics are observed and analyzed.

Sign in / Sign up

Export Citation Format

Share Document