Graphene and chiral nematic liquid crystals: A focus on lasing

© The Royal Society of Chemistry 2015. This work presents the interaction of self-assembled liquid crystalline (LC) unidimensional photonic structures on the surface of polycrystalline graphene. Further, this surface effect is studied through different substrate geometries in the test devices. Primarily, these devices are characterised through polarizing optical microscopy (POM) and their laser emission features in the dye-doped chiral systems. Then the conductive nature of graphene is utilized to apply external electric fields to the photonic medium and its effect is envisaged. These graphene-based devices demonstrate a unique result in polarizing optical micrographs and electro-optic responses which indicates the presence of multidirectional domain formations. Additionally, the LC band-edge lasing from graphene cells is found to be anisotropic and depends on the directionality of the optical pump. This work attempts to lay the foundation for the implementation of a new class of defused chiral nematic liquid crystal based devices e.g. optical filters, notch filters, colour reflectors, and light shutters and may add toward the knowledge base necessary in the substitution of Indium Tin Oxide (ITO) with graphene in traditional LC based display devices.This work was carried out under the GRAPHTED project which is funded by the Engineering and Physical Sciences Research Council UK (project ref. EP/K016636/1, Grant No. EP/H047565/ 1). A. A. K. would like to thank the Higher Education of Pakistan (HEC), P. R. K. acknowledges Lindemann Trust Fellowship. A. A. K. and P. R. K. acknowledge the Cambridge Commonwealth, European and International Trust and for the nancial suppo

Conductivity studies on the effect of a nematic liquid crystal on polyvinyl alcohol-based electrolytes

Recently, a few studies have shown that the introduction of liquid crystals (LCs) in polymer electrolytes would lead to an increase in the chain mobility and the ionic conductivity. It is believed that this enhancement of the polymer electrolyte performance is greatly influenced by the order parameter of the liquid crystal in this system. In this study, a deuterated 4-pentyl-4'-cyanobiphenyl (5CB-d2) nematic liquid crystal-doped polyvinyl alcohol (PVA) polymer electrolyte were prepared. The orientational order of the nematic liquid crystal is then investigated via the quadrupolar splittings of the deuterium Nuclear Magnetic Resonance (NMR) spectra. The quadrapolar splitting, which is directly related to the orientational order of the liquid crystal director, was measured and compared between the embedded 5CB-d2 in the PVA electrolyte to that of the pure 5CB-d2. The conductivity of a 5CB-d2 embedded in PVA reached up to 3.28×10-1 S/cm compare to that of without 5CB-d2 which is only 2.89×10-1S/cm. The presence of 5CB-d2 in the PVA polymer electrolyte improved the electrical conductivity of the mixture through an improved charge transfer mechanism, which improves its electrical properties, a criterion useful for a device that needs high conductivity. © (2014) Trans Tech Publications, Switzerland

Graphene and chiral nematic liquid crystals: A focus on lasing

© The Royal Society of Chemistry 2015. This work presents the interaction of self-assembled liquid crystalline (LC) unidimensional photonic structures on the surface of polycrystalline graphene. Further, this surface effect is studied through different substrate geometries in the test devices. Primarily, these devices are characterised through polarizing optical microscopy (POM) and their laser emission features in the dye-doped chiral systems. Then the conductive nature of graphene is utilized to apply external electric fields to the photonic medium and its effect is envisaged. These graphene-based devices demonstrate a unique result in polarizing optical micrographs and electro-optic responses which indicates the presence of multidirectional domain formations. Additionally, the LC band-edge lasing from graphene cells is found to be anisotropic and depends on the directionality of the optical pump. This work attempts to lay the foundation for the implementation of a new class of defused chiral nematic liquid crystal based devices e.g. optical filters, notch filters, colour reflectors, and light shutters and may add toward the knowledge base necessary in the substitution of Indium Tin Oxide (ITO) with graphene in traditional LC based display devices

Studies on relation between columnar order and electrical conductivity in HAT6 discotic liquid crystals using temperature-dependent Raman spectroscopy and DFT calculations

The vibrational property of 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6) discotic liquid crystal (DLC) material is investigated in this research by using temperature-dependent Raman spectroscopy technique. One-dimensional (1D) charge transport mechanism in the DLC molecules is enabled in the columnar liquid crystalline (Dh) phase. The result indicates a high core-to-core correlation in the liquid crystal columnar phase, which has a ‘memory’ like effect that extends into isotropic phase at femtosecond timescale. This correlation is also confirmed through electrical conductivity measurement of DLCs, in which the electrical conductivity is enhanced in the DLC phase. DFT simulation was also carried out in order to elucidate the basic properties of HAT6 such as the band gap in the light of Raman spectra. An interesting outcome is that a freely unspecified boundary model produces in a more flexible molecule, resulting in a reduced band gap. Thus, this work provides an understanding of relationship between columnar order and electrical conductivity of HAT6 molecule, and potential strategy for design of DLCs in electronics application

Induced alignment of reactive mesogen-based polymer electrolyte for dye-sensitised solar cells

Liquid crystalline materials are interesting organic molecules possessing anisotropic behaviour. The materials undergo self-assembly forming highly ordered structure, which from the opto-electronic applications' point of view, hold promising future. By controlling the functionality or the mesophase of the liquid crystal materials, it is possible to develop specific device architectures. So far, controlling the morphologies of organic materials for electronic applications has proven to be difficult. Here, we prepared a liquid crystal-based polymer template using polymer alignment layer and electric field. The resultant morphology is closely related to the fabrication technique which can be further modified to suit particular device applications. The mesophase characteristics and morphologies of these materials are characterised using polarising optical microscopy, atomic force microscopy and scanning electron microscopy. Next, we utilised these polymer electrolytes in dye-sensitised solar cells as a potential application. Device performance such as open-circuit voltage, short-circuit current, fill-factor and power conversion efficiencies also showed strong dependence on the structure of the polymer scaffold. Hierarchical polymer electrolyte structures were prepared using reactive mesogen assisted by Smectic A liquid crystals. The morphology of these hierarchical structures wa controlled by the use of alignment layers on the substrate or by applying electric fields. The highest power conversion efficiency achieved was 5.02 % in cells with electric field induced alignment, as compared to 4.57 % for the polyimide aligned sample. This can be attributed to the higher porosity in the case of electric field aligned sample whereas for the polyimide aligned sample, despite having a more ordered pores, the width between the pores are comparatively smaller.The authors would like to thank Organica and Dyesol for providing the materials used in this experiment. A. A. K. and G. R. would like to thank the Cambridge Commonwealth European and International Trust (CCEIT). A. A. K. would also like to acknowledge the HEC (Pakistan) for financial support. E. T. would like to thank Trinity Hall, University of Cambridge for financial support

Induced alignment of reactive mesogen-based polymer electrolyte for dye-sensitised solar cells

Liquid crystalline materials are interesting organic molecules possessing anisotropic behaviour. The materials undergo self-assembly forming highly ordered structure, which from the opto-electronic applications' point of view, hold promising future. By controlling the functionality or the mesophase of the liquid crystal materials, it is possible to develop specific device architectures. So far, controlling the morphologies of organic materials for electronic applications has proven to be difficult. Here, we prepared a liquid crystal-based polymer template using polymer alignment layer and electric field. The resultant morphology is closely related to the fabrication technique which can be further modified to suit particular device applications. The mesophase characteristics and morphologies of these materials are characterised using polarising optical microscopy, atomic force microscopy and scanning electron microscopy. Next, we utilised these polymer electrolytes in dye-sensitised solar cells as a potential application. Device performance such as open-circuit voltage, short-circuit current, fill-factor and power conversion efficiencies also showed strong dependence on the structure of the polymer scaffold. Hierarchical polymer electrolyte structures were prepared using reactive mesogen assisted by Smectic A liquid crystals. The morphology of these hierarchical structures wa controlled by the use of alignment layers on the substrate or by applying electric fields. The highest power conversion efficiency achieved was 5.02 % in cells with electric field induced alignment, as compared to 4.57 % for the polyimide aligned sample. This can be attributed to the higher porosity in the case of electric field aligned sample whereas for the polyimide aligned sample, despite having a more ordered pores, the width between the pores are comparatively smaller

Thrombotic and hemorrhagic complications of COVID-19 in adults hospitalized in high-income countries compared with those in adults hospitalized in low- and middle-income countries in an international registry

Background: COVID-19 has been associated with a broad range of thromboembolic, ischemic, and hemorrhagic complications (coagulopathy complications). Most studies have focused on patients with severe disease from high-income countries (HICs). Objectives: The main aims were to compare the frequency of coagulopathy complications in developing countries (low- and middle-income countries [LMICs]) with those in HICs, delineate the frequency across a range of treatment levels, and determine associations with in-hospital mortality. Methods: Adult patients enrolled in an observational, multinational registry, the International Severe Acute Respiratory and Emerging Infections COVID-19 study, between January 1, 2020, and September 15, 2021, met inclusion criteria, including admission to a hospital for laboratory-confirmed, acute COVID-19 and data on complications and survival. The advanced-treatment cohort received care, such as admission to the intensive care unit, mechanical ventilation, or inotropes or vasopressors; the basic-treatment cohort did not receive any of these interventions. Results: The study population included 495,682 patients from 52 countries, with 63% from LMICs and 85% in the basic treatment cohort. The frequency of coagulopathy complications was higher in HICs (0.76%-3.4%) than in LMICs (0.09%-1.22%). Complications were more frequent in the advanced-treatment cohort than in the basic-treatment cohort. Coagulopathy complications were associated with increased in-hospital mortality (odds ratio, 1.58; 95% CI, 1.52-1.64). The increased mortality associated with these complications was higher in LMICs (58.5%) than in HICs (35.4%). After controlling for coagulopathy complications, treatment intensity, and multiple other factors, the mortality was higher among patients in LMICs than among patients in HICs (odds ratio, 1.45; 95% CI, 1.39-1.51). Conclusion: In a large, international registry of patients hospitalized for COVID-19, coagulopathy complications were more frequent in HICs than in LMICs (developing countries). Increased mortality associated with coagulopathy complications was of a greater magnitude among patients in LMICs. Additional research is needed regarding timely diagnosis of and intervention for coagulation derangements associated with COVID-19, particularly for limited-resource settings