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Metal halide perovskite solar cells (PSCs) are an emerging photovoltaic technology with the potential to disrupt the mature silicon solar cell market. Great improvements in device performance over the past few years, thanks to the development of fabrication protocols1-3, chemical compositions4,5 and phase stabilization methods6-10, have made PSCs one of the most efficient and low-cost solution-processable photovoltaic technologies. However, the light-harvesting performance of these devices is still limited by excessive charge carrier recombination. Despite much effort, the performance of the best-performing PSCs is capped by relatively low fill factors and high open-circuit voltage deficits (the radiative open-circuit voltage limit minus the high open-circuit voltage)11. Improvements in charge carrier management, which is closely tied to the fill factor and the open-circuit voltage, thus provide a path towards increasing the device performance of PSCs, and reaching their theoretical efficiency limit12. Here we report a holistic approach to improving the performance of PSCs through enhanced charge carrier management. First, we develop an electron transport layer with an ideal film coverage, thickness and composition by tuning the chemical bath deposition of tin dioxide (SnO2). Second, we decouple the passivation strategy between the bulk and the interface, leading to improved properties, while minimizing the bandgap penalty. In forward bias, our devices exhibit an electroluminescence external quantum efficiency of up to 17.2 per cent and an electroluminescence energy conversion efficiency of up to 21.6 per cent. As solar cells, they achieve a certified power conversion efficiency of 25.2 per cent, corresponding to 80.5 per cent of the thermodynamic limit of its bandgap.
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Liquid crystals (LCs) are anisotropic fluids that combine the long-range order of crystals with the mobility of liquids1,2. This combination of properties has been widely used to create reconfigurable materials that optically report information about their environment, such as changes in electric fields (smart-phone displays) 3 , temperature (thermometers) 4 or mechanical shear 5 , and the arrival of chemical and biological stimuli (sensors)6,7. An unmet need exists, however, for responsive materials that not only report their environment but also transform it through self-regulated chemical interactions. Here we show that a range of stimuli can trigger pulsatile (transient) or continuous release of microcargo (aqueous microdroplets or solid microparticles and their chemical contents) that is trapped initially within LCs. The resulting LC materials self-report and self-regulate their chemical response to targeted physical, chemical and biological events in ways that can be preprogrammed through an interplay of elastic, electrical double-layer, buoyant and shear forces in diverse geometries (such as wells, films and emulsion droplets). These LC materials can carry out complex functions that go beyond the capabilities of conventional materials used for controlled microcargo release, such as optically reporting a stimulus (for example, mechanical shear stresses generated by motile bacteria) and then responding in a self-regulated manner via a feedback loop (for example, to release the minimum amount of biocidal agent required to cause bacterial cell death).
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Cristais Líquidos/química , Liberação Controlada de Fármacos/efeitos da radiação , Elasticidade , Eletricidade , Escherichia coli/fisiologia , Dedos/fisiologia , Temperatura Alta , Humanos , Luz , Cristais Líquidos/efeitos da radiação , TatoRESUMO
BACKGROUND: This study aimed to investigate the characteristics of occupational injuries based on fatality, sex, and classification of occupations among construction workers using workers' compensation (WC) insurance data in South Korea. METHODS: We collected WC insurance data from the Korea Workers' Compensation & Welfare Service for all construction workers between 2009 and 2018. Data from 158,947 accepted claims for occupational injury were extracted, and the demographic features, occupational injury types, and annual trends were analyzed for fatal and nonfatal cases. The annual incidence and mortality trends of occupational injury were estimated using negative binomial regression and Poisson regression models, for injury incidence and mortality respectively. RESULTS: Among a total of 158,947 occupational injury cases, there were 155,772 (98%) nonfatal injuries and 3175 (2%) fatal injuries. For all occupational injuries, Construction Elementary Workers (6th Korean Standard Classification of Occupations (KSCO) 910; 45.7%) was the most frequent occupation, followed by Construction-Related Technical Workers (6th KSCO 772; 39.2%). The most frequent injury type was a fracture, followed by ruptures or lacerations and contusions. The incidence of all occupational injuries increased from 700.36 per 100,000 persons in 2009 to 1,195.98 per 100,000 persons in 2018. Further, deaths from injuries at work followed a significantly increasing annual trend [mortality rate ratio 1.04 (95% CI: 1.03-1.05)] from 2009 to 2018. CONCLUSION: The over two-thirds increased incidence of occupational injuries and significantly increasing mortality trends for occupational injuries during the last 10 years indicate the need for aggressive intervention in occupational safety and health management within the Korean construction industry.
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Indústria da Construção , Traumatismos Ocupacionais , Humanos , Traumatismos Ocupacionais/epidemiologia , Ocupações , República da Coreia/epidemiologia , Indenização aos Trabalhadores , Acidentes de TrabalhoRESUMO
Polyelectrolytes adsorbed at soft interfaces are used in contexts such as materials synthesis, stabilization of emulsions, and control of rheology. Here, we explore how polyelectrolyte adsorption to aqueous interfaces of thermotropic liquid crystals (LCs) influences surfactant-stabilized aqueous microdroplets that are elastically trapped within the LCs. We find that adsorption of poly(diallyldimethylammonium chloride) (PDDA) to the interface of a nematic phase of 4-cyano-4'-pentylbiphenyl (5CB) triggers the ejection of microdroplets decorated with sodium dodecylsulfate (SDS), consistent with an attractive electrical double layer interaction between the microdroplets and LC interface. The concentration of PDDA that triggers release of the microdroplets (millimolar), however, is three orders of magnitude higher than that which saturates the LC interfacial charge (micromolar). Observation of a transient reorientation of the LC during escape of microdroplets leads us to conclude that complexes of PDDA and SDS form at the LC interface and thereby regulate interfacial charge and microdroplet escape. Poly(sodium 4-styrenesulfonate) (PSS) also triggers escape of dodecyltrimethylammonium bromide (DTAB)-decorated aqueous microdroplets from 5CB with dynamics consistent with the formation of interfacial polyelectrolyte-surfactant complexes. In contrast to PDDA-SDS, however, we do not observe a transient reorientation of the LC when using PSS-DTAB, reflecting weak association of DTAB and PSS and slow kinetics of formation of PSS-DTAB complexes. Our results reveal the central role of polyelectrolyte-surfactant dynamics in regulating the escape of the microdroplets and, more broadly, that LCs offer the basis of a novel probe of the structure and properties of polyelectrolyte-surfactant complexes at interfaces. We demonstrate the utility of these new insights by triggering the ejection of microdroplets from LCs using peptide-polymer amphiphiles that switch their net charge upon being processed by enzymes. Overall, our results provide fresh insight into the formation of polyelectrolyte-surfactant complexes at aqueous-LC interfaces and new principles for the design of responsive soft matter.
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Cristais Líquidos , Adsorção , Polieletrólitos , Tensoativos , ÁguaRESUMO
Since Antarctica and the surrounding Southern Ocean are facing global climate change, biota inhabiting those coastal regions is now challenged by environmental fluctuations including coastal freshening. In this study, the effects of salinity range of 0-75 (practical salinity unit, PSU) on the Antarctic harpacticoid copepod Tigriopus kingsejongensis was investigated by measurement of 96 h survival rate, lifespan, and sex ratio with further analysis of multigenerational growth parameters and mRNA expressions under salinity of 15-45. Different stages of the copepods (i.e., nauplius, male, and female) generally showed tolerance to hypo- and hypersalinity, wherein female copepods were more tolerant than males when exposed to salinity fluctuations. Lifespan was significantly shortened by hypo- and hypersalinity compared to control salinity (34), but there was no significant difference in the sex ratio between salinity treatments. Multigenerational experiments across five generations revealed that exposure to salinities of 15 and 45 reduced body length compared to that in control salinity and the first generation of each salinity group. Our results provide evidence regarding T. kingsejongensis on their preferred salinity ranges, physiological limit to salinity fluctuations, and population dynamics in future salinity.
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Copépodes , Animais , Regiões Antárticas , Feminino , Masculino , SalinidadeRESUMO
We report that incubation of aqueous dispersions of supramolecular assemblies formed by synthetic alkyl triazole-based amphiphiles against interfaces of thermotropic liquid crystals (LCs; 4-cyano-4'-pentylbiphenyl) triggers spatially localized (micrometer-scale) and transient (subsecond) flashes of light to be transmitted through the LC. Analysis of the spatiotemporal response of the LC supports our proposal that each optical "blinking" event results from collision of a single supramolecular assembly with the LC interface. Particle tracking at the LC interface confirmed that collision and subsequent spreading of amphiphiles at the interface generates a surface pressure-driven interfacial flow (Marangoni flow) that causes transient reorientation of LC and generation of a bright optical flash between crossed polarizers. We also found that dispersions of phospholipid vesicles cause "blinks". When using vesicles formed from 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), we measured the frequency of blinking to decrease proportionally with the number density of vesicles in the aqueous phase, consistent with single vesicle events, with the lifetime of each blink dependent on vesicle size (800 ± 80 nm to 150 ± 30 nm). For 100 µM of DLPC, we measured vesicles with a diameter of 940 ± 290 nm to generate 47 ± 9 blinks min-1 mm-2, revealing that the fraction of vesicle collisions resulting in fusion with the LC interface is â¼10-3. Overall, the results in this paper unmask new nonequilibrium behaviors of amphiphiles at LC interfaces, and provide fresh approaches for exploring the dynamic interactions of supramolecular assemblies of amphiphiles with fluid interfaces at the single-event level.
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Two new heterometallic metal-organic frameworks (MOFs), LnZnTPO 1 and 2, and two homometallic MOFs, LnTPO 3 and 4 (Ln=Eu for 1 and 3, and Tb for 2 and 4; H3 TPO=tris(4-carboxyphenyl)phosphine oxide) were synthesized, and their structures and properties were analyzed. They were prepared by solvothermal reaction of the C3 -symmetric ligand H3 TPO with the corresponding metal ion(s) (a mixture of Ln3+ and Zn2+ for 1 and 2, and Ln3+ alone for 3 and 4). Single-crystal XRD (SXRD) analysis revealed that 1 and 3 are isostructural to 2 and 4, respectively. TGA showed that the framework is thermally stable up to about 400 °C for 1 and 2, and about 450 °C for 3 and 4. PXRD analysis showed their pore-structure distortions without noticeable framework-structure changes during drying processes. The shapes of gas sorption isotherms for 1 and 3 are almost identical to those for 2 and 4, respectively. Solvothermal immersion of 1 and 2 in Tb3+ and Eu3+ solutions resulted in the framework metal-ion exchange affording 4 and 3, respectively, as confirmed by photoluminescence (PL), PXRD, IR, inductively coupled plasma atomic emission spectroscopy (ICP-AES), and energy-dispersive X-ray (EDX) analyses.
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Liquid crystalline (LC) oils offer the basis of stimuli-responsive LC-in-water emulsions. Although past studies have explored the properties of single-phase LC emulsions, few studies have focused on complex multicompartment emulsions containing co-existing isotropic and LC domains. In this paper, we report a study of multiphase emulsions using LCs and immiscible perfluoroalkanes dispersed in water or glycerol (the latter continuous phase is used to enable characterization). We found that the nematogen 4'-pentyl-4-biphenylcarbonitrile (5CB) anchors homeotropically (perpendicularly) and weakly at liquid perfluorononane (F9) interfaces, consistent with the smectic layering of 5CB molecules. The proposed role of smectic layering is supported by experiments performed with 4-(trans-4-pentylcyclohexyl)benzonitrile, a nematogen that possesses a cyclohexyl group that frustrates the smectic packing and leads to tilted orientations at the F9 interface. By employing perfluorocarbon and hydrocarbon surfactants in combination with multiphase 5CB and F9 emulsion droplets dispersed in a continuous water or glycerol phase, we observe a range of emulsion droplet morphologies to form, including core-shell and Janus structures, with internal organizations that reflect an interplay of interfacial (anchoring energies; F9 and glycerol) and elastic energies within the confines of the geometry of the emulsion droplet. By comparing experimental observations to simulations of the LC-perfluorocarbon droplets based on a Landau-de Gennes model of the free energy, we place bounds on the orientation-dependent interfacial energies that underlie the internal ordering of these complex emulsions. Additionally, by forming core-shells emulsion droplets from 5CB (shell) and perfluoroheptane (cores), we demonstrate how a liquid-to-vapor phase transition in the perfluorocarbon core can be used to actuate the droplet and rapidly thin the nematic shell. Overall, the results reported in this paper demonstrate that multiphase LC emulsions formed from mixtures of perfluoroalkanes and LCs provide new opportunities to engineer hierarchical and stimuli-responsive emulsion systems.
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Liquid crystals (LCs) are fluids within which molecules exhibit long-range orientational order, leading to anisotropic properties such as optical birefringence and curvature elasticity. Because the ordering of molecules within LCs can be altered by weak external stimuli, LCs have been widely used to create soft matter systems that respond optically to electric fields (LC display), temperature (LC thermometer) or molecular adsorbates (LC chemical sensor). More recent studies, however, have moved beyond investigations of optical responses of LCs to explore the design of complex LC-based soft matter systems that offer the potential to realize more sophisticated functions (e.g., autonomous, self-regulating chemical responses to mechanical stimuli) by directing the interactions of small molecules, synthetic colloids and living cells dispersed within the bulk of LCs or at their interfaces. These studies are also increasingly focusing on LC systems driven beyond equilibrium states. This review presents one perspective on these advances, with an emphasis on the discovery of fundamental phenomena that may enable new technologies. Three areas of progress are highlighted; (i) directed assembly of amphiphilic molecules either within topological defects of LCs or at aqueous interfaces of LCs, (ii) templated polymerization in LCs via chemical vapor deposition, an approach that overcomes fundamental challenges related to control of LC phase behavior during polymerization, and (iii) studies of colloids in LCs, including chiral colloids, soft colloids that are strained by LCs, and active colloids that are driven into organized states by dissipation of energy (e.g. bacteria). These examples, and key unresolved issues discussed at the end of this perspective, serve to convey the message that soft matter systems that integrate ideas from LC, surfactant, polymer and colloid sciences define fertile territory for fundamental studies and creation of future transformative technologies.
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We report that mixtures of perfluorocarbon oils and hydrocarbon mesogens can be used to prepare multi-compartment (Janus) emulsion drops comprising coexisting nematic liquid crystalline (LC) and isotropic oil phases. The droplets exhibit stable spherical shapes with internal Janus-type morphologies that can be tuned widely through changes in temperature or adsorbates. In particular, we observe evidence of preferential adsorption of hydrocarbon or fluorocarbon surfactants on the interfaces of nematic versus isotropic domains, respectively, providing added control over the droplet structure. Comparisons of experiments and numerical simulations using a Landau-de Gennes continuum model provide insight into the relative importance of the LC elasticity and orientational-dependent interfacial energies on droplet morphologies and properties. We show that the hierarchical organization of the LC compartments generates optical properties and responsiveness not found in emulsions of isotropic oils.
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Oxygen vacancies (OV) are native defects in transition metal (TM) oxides and their presence has a critical effect on the physicochemical properties of the oxide. Metal oxides are commonly used in lithium-ion battery (LIB) cathodes and there is still a lack of understanding of the role of OVs in LIB research field. Here, we report on the behavior of OVs in a single-crystal LIB cathode during the non-equilibrium states of charge and discharge. We found that microcrack evolution in a single crystal occurs due to OV condensation in specific crystallographic orientations generated by the continuous migration of OVs and TM ions. Moreover, understanding the effects of the presence and diffusion of OVs in metal oxides enables the elucidation of most of the conventional mechanisms of capacity fading in LIBs and provides new insights for new electrochemical applications.
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Liquid crystals (LCs) offer the basis of stimuli-responsive materials that can amplify targeted molecular events into macroscopic outputs. However, general and versatile design principles are needed to realize the full potential of these materials. To this end, we report the synthesis of two homopolymers with mesogenic side chains that can be cleaved upon exposure to either H2 O2 (polymer P1) or UV light (polymer P2). Optical measurements reveal that the polymers dissolve in bulk LC and spontaneously assemble at nematic LC-aqueous interfaces to impose a perpendicular orientation on the LCs. Subsequent addition of H2 O2 to the aqueous phase or exposure of the LC to UV was shown to trigger a surface-driven ordering transition to a planar orientation and an accompanying macroscopic optical output. Differences in the dynamics of the response to each stimulus are consistent with sequential processing of P1 at the LC-aqueous interface (H2 O2 ) and simultaneous transformation of P2 within the LC (UV). The versatility of the approach is demonstrated by creating stimuli-responsive LCs as films or microdroplets, and by dissolving mixtures of P1 and P2 into LCs to create LC materials that respond to two stimuli. Overall, our results validate a simple and generalizable approach to the rational design of polymers that can be used to program stimuli-responsiveness into LC materials.
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We report an investigation of the influence of aqueous solutions of amphiphilic oligomers on the ordering of micrometer-thick films of thermotropic liquid crystals (LCs), thus addressing the gap in knowledge arising from previous studies of the interactions of monomeric and polymeric amphiphiles with LCs. Specifically, we synthesized amphiphilic oligomers (with decyl hydrophobic and pentaethylene glycol hydrophilic domains) in monomer, dimer, and trimer forms, and incubated aqueous solutions of the oligomers against nematic films of 4'-pentyl-4-biphenylcarbonitrile (5CB). All amphiphilic oligomers caused sequential surface-driven orientational (planar to homeotropic) and then bulk phase transitions (nematic to isotropic) with dynamics depending strongly on the degree of oligomerization. The dynamics of the orientational transitions accelerated from monomer to trimer, consistent with the effects of an increase in adsorption free energy. The mechanism underlying the orientational transition, however, involved a decrease in anchoring energy and not change in the easy axis of the LC. In contrast, the rate of the phase transition induced by absorption of oligomers into the LC decreased from monomer to trimer, suggesting that constraints on configurational degrees of freedom influence the absorption free energies of the oligomers. Interestingly, the oligomer-induced transition from the nematic to isotropic phase of 5CB was observed to nucleate at the aqueous-5CB interface, consistent with surface-induced disorder underlying the above-reported decrease in anchoring energy caused by the oligomers. Finally, we provided proof-of-concept experiments of the triggering of LCs using a trimeric amphiphile that is photocleaved by UV illumination into monomeric fragments. Overall, our results provide insight into the rational design of oligomers that can be used as triggers to create responsive LCs.
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BACKGROUND: Asbestos exposure causes asbestos-related diseases (ARDs) including asbestosis, malignant mesothelioma, lung cancer, laryngeal cancer, and ovarian cancer. Although Korea used substantial amounts of asbestos in the past, no study has focused on its occupational burden of disease (OBD). Therefore, this study aimed to determine the OBDs of ARDs in Korea. METHODS: The CARcinogen Exposure (CAREX) database was used to determine the proportion of exposed population. Relative risks for lung cancer, laryngeal cancer, and ovarian cancer were used to determine the population-attributable fraction. Data for deaths caused by ARDs during 1998-2013 were obtained from the World Health Organization mortality database. The potential years of life lost (PYLL) and annual average PYLL (APYLL) indicated OBDs. RESULTS: In Korea, the number of ARD-attributable deaths and PYLL due to all ARDs during 1998-2013 were 4,492 and 71,763.7, respectively. The number of attributable deaths and PYLL due to asbestosis, malignant mesothelioma, lung cancer, laryngeal cancer, and ovarian cancer were 37 and 554.2, 808 and 15,877.0, 3,256 and 47,375.9, 120 and 1,605.5, and 271 and 6,331.1, respectively; additionally, the APYLL were 15.0, 19.7, 14.6, 13.4, and 23.4, respectively, and the average age at death was 70.4, 62.6, 69.1, 69.9, and 61.8, respectively. Our study showed that although the use of asbestos has ceased in Korea, the incidence of ARDs tends to increase. CONCLUSION: Therefore, efforts to reduce future OBDs of ARDs, including early detection and proper management of ARDs, are needed in Korea.
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Amianto/efeitos adversos , Doenças Profissionais/induzido quimicamente , Idoso , Asbestose , Europa (Continente) , Feminino , Humanos , Neoplasias Laríngeas , Neoplasias Pulmonares , Masculino , Mesotelioma , Pessoa de Meia-Idade , Exposição Ocupacional , Neoplasias Ovarianas , República da CoreiaRESUMO
We report an investigation of the active motion of silica-palladium Janus particles (JPs) adsorbed at interfaces formed between nematic liquid crystals (LCs) and aqueous phases containing hydrogen peroxide (H2O2). In comparison to isotropic oil-aqueous interfaces, we observe the elasticity and anisotropic viscosity of the nematic phase to change qualitatively the active motion of the JPs at the LC interfaces. Although contact line pinning on the surface of the JPs is observed to restrict out-of-plane rotational diffusion of the JPs at LC interfaces, orientational anchoring of nematic LCs on the silica (planar) and palladium (homeotropic) hemispheres biases JP in-plane orientations to generate active motion almost exclusively along the director of the LC at low concentrations of H2O2 (0.5 wt %). In contrast, displacements perpendicular to the director exhibit the characteristics of Brownian diffusion. At higher concentrations of H2O2 (1-3 wt %), we observe an increasing population of JPs propelled parallel and perpendicular to the LC director in a manner consistent with active motion. In addition, under these conditions, we also observe a subpopulation of JPs (approximately 10%) that exhibit active motion exclusively perpendicular to the LC director. These results are discussed in light of independent measurements of the distribution of azimuthal orientations of the JPs at the LC interfaces and calculations of the elastic energies that bias JP orientations. We also contrast our observations at LC interfaces to past studies of self-propulsion of particles within and at the interfaces of isotropic liquids.
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We report on the internal configurations of droplets of nematic liquid crystals (LCs; 10-50 µm-in-diameter; comprised of 4-cyano-4'-pentylbiphenyl and 4-(3-acryloyloxypropyloxy)benzoic acid 2-methyl-1,4-phenylene ester) sedimented from aqueous solutions of sodium dodecyl sulfate (SDS) onto interfaces formed with pure glycerol. We observed a family of internal LC droplet configurations and topological defects consistent with a remarkably abrupt transition from homeotropic (perpendicular) to tangential anchoring on the surface of the LC droplets in the interfacial environment. Calculations of the interdiffusion of water and glycerol at the aqueous-glycerol interface revealed the thickness of the diffuse interfacial region of the two miscible liquids to be small (0.2-0.5 µm) compared to the diameters of the LC droplets on the experimental time-scale (15-120 minutes), leading us to hypothesize that the patterned surface anchoring was induced by gradients in concentration of SDS and glycerol across the diameter of the LC droplets in the interfacial region. This hypothesis received additional support from experiments in which the time of sedimentation of the LC droplets onto the interface was systematically increased and the droplets were photo-polymerized to preserve their configurations: the configurations of the LC droplets were consistent with a time-dependent decrease in the fraction of the surface area of each droplet exhibiting homeotropic anchoring. Specifically, LC droplets with <10% surface area with tangential anchoring exhibited a bulk point defect within the LC droplet, whereas droplets with >10% surface area with tangential anchoring exhibited a boojum defect within the tangential region and a disclination loop separated the regions with tangential and homeotropic anchoring. The topological charge of these LC droplet configurations was found to be consistent with the geometrical theorems of Poincaré and Gauss and also well-described by computer simulations performed by minimization of a Landau-de Gennes free energy. Additional experimental observations (e.g., formation of "Janus-like" particles with one hemisphere exhibiting tangential anchoring and the other perpendicular anchoring) and simulations (e.g., a size-dependent set of LC droplet configurations with <10% surface area exhibiting tangential anchoring) support our general conclusion that placement of LC droplets into miscible liquid-liquid interfacial environments with compositional gradients can lead to a rich set of LC droplet configurations with symmetries and optical characteristics that are not encountered in LC droplet systems in homogeneous, bulk environments. Our results also reveal that translocation of LC droplets across liquid-liquid interfaces can define new transition pathways that connect distinct configurations of LC droplets.
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The nanoscopic structure of the cores of topological defects in anisotropic condensed matter is an unresolved issue, although a number of theoretical predictions have been reported. In the experimental study reported in this Letter, we template the assembly of amphiphilic molecules from the cores of defects in liquid crystals and thereby provide the first experimental evidence that the cores of singular defects that appear optically to be points (with strength m=+1) are nanometer-sized closed-loop, disclination lines. We also analyze this result in the context of a model that describes the influence of amphiphilic assemblies on the free energy and stability of the defects. Overall, our experimental results and theoretical predictions reveal that the cores of defects with opposite strengths (e.g., m=+1 vs m=-1) differ in ways that profoundly influence processes of molecular self-assembly.
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The synthesis and characterisation of the nonsymmetric liquid crystal dimer, 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl)hexane (CB6OCB) is reported. An enantiotropic nematic (N)-twist-bend nematic (NTB) phase transition is observed at 109 °C and a nematic-isotropic phase transition at 153 °C. The NTB phase assignment has been confirmed using polarised light microscopy, freeze fracture transmission electron microscopy (FFTEM), (2)H-NMR spectroscopy, and X-ray diffraction. The effective molecular length in both the NTB and N phases indicates a locally intercalated arrangement of the molecules, and the helicoidal pitch length in the NTB phase is estimated to be 8.9 nm. The surface anchoring properties of CB6OCB on a number of aligning layers is reported. A Landau model is applied to describe high-resolution heat capacity measurements in the vicinity of the NTB-N phase transition. Both the theory and heat capacity measurements agree with a very weak first-order phase transition. A complementary extended molecular field theory was found to be in suggestive accord with the (2)H-NMR studies of CB6OCB-d2, and those already known for CB7CB-d4. These include the reduced transition temperature, TNTBN/TNI, the order parameter of the mesogenic arms in the N phase close to the NTB-N transition, and the order parameter with respect to the helix axis which is related to the conical angle for the NTB phase.
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Galactose , Glomerulonefrite por IGA , Humanos , Imunoglobulina A , Glomérulos Renais , Doadores de TecidosRESUMO
We investigate the origin of "secondary disclinations" that were recently described as new evidence of a biaxial nematic phase in an oxadiazole bent-core thermotropic liquid crystal C7. Using an assortment of optical techniques such as polarizing optical microscopy, LC PolScope, and fluorescence confocal polarizing microscopy, we demonstrate that the secondary disclinations represent non-singular domain walls formed in a uniaxial nematic phase during the surface anchoring transition, in which surface orientation of the director changes from tangential (parallel to the bounding plates) to tilted. Each domain wall separates two regions with the director tilted in opposite azimuthal directions. At the centre of the wall, the director remains parallel to the bounding plates. The domain walls can be easily removed by applying a moderate electric field. The anchoring transition is explained by the balance of (a) the intrinsic perpendicular surface anchoring produced by the polyimide aligning layer and (b) tangential alignment caused by ionic impurities forming electric double layers. The model is supported by the fact that the temperature of the tangentially tilted anchoring transition decreases as the cell thickness increases and as the concentration of ionic species (added salt) increases. We also demonstrate that the surface alignment is strongly affected by thermal degradation of the samples. This study shows that C7 exhibits only a uniaxial nematic phase and demonstrates yet another mechanism (formation of "secondary disclinations") by which a uniaxial nematic phase can mimic a biaxial nematic behaviour.