Comparative analysis of anisotropic material properties of uniaxial nematics formed by flexible dimers and rod-like monomers

We report temperature dependencies of material properties such as dielectric anisotropy, birefringence, splay (K₁₁), twist (K₂₂), and bend (K₃₃) elastic constants of the uniaxial nematic (N) phase formed by flexible dimers of DTC5C9 and compare their behavior to that of a corresponding monomer MCT5. DTC5C9 forms a twist-bend nematic (Ntb) at temperatures below the N phase. Anisotropic properties of MCT5 are typical of the rod-like mesogens. In particular, birefringence increases as the temperature is reduced, following the classic behavior, described by Haller. The elastic constants also follow the standard behavior, with their ratios being practically temperature-independent. In contrast, DTC5C9 shows a dramatic departure from the standard case. Birefringence changes non-monotonously with temperature, decreasing on approaching the N-Ntb phase transition. K₃₃ decreases strongly to 0.4 pN near the N - Ntb transition, although remains finite. The ratios of the elastic constants in DTC5C9 show a strong temperature dependence that can be associated with the bend-induced changes in the orientational distribution function. The measured elastic properties are consistent with the tendency of the dimeric molecules to adopt bent configurations that give rise to the Ntb phase

Dielectric properties of liquid crystalline dimer mixtures exhibiting the nematic and twist-bend nematic phases

A detailed investigation of the thermal and dielectric properties of a series of binary mixtures exhibiting the nematic ( N ) and twist-bend nematic ( N TB ) liquid crystal phases is presented. The mixtures consist of an achiral, dimeric liquid crystal CB7CB, which forms the nematic and twist-bend nematic phases, and a calamitic liquid crystal 5CB, which shows the nematic phase. As the concentration of the calamitic liquid crystal is increased, the transition temperatures decrease linearly, and the width of the nematic phase increases. The enthalpies of phase transitions obtained from DSC measurements show that on increasing the concentration of 5CB in the binary mixtures, the enthalpy associated with the N − N TB phase transitions reduces considerably compared to a clear first-order N − N TB transition in pure CB7CB. The real and imaginary parts of the dielectric permittivity are measured as a function of frequency from 100 Hz to 2 MHz in the nematic and twist-bend nematic phases in planar and homeotropic devices. A significant decrease in the average dielectric permittivity as a function of temperature for mixtures forming the N TB phase is observed. Measurements of the imaginary part of the dielectric permittivity show a relaxation peak in the measured frequency window for all of the mixtures exhibiting the N TB phase. The activation energy associated with this relaxation process is calculated and is shown to remain constant irrespective of the composition of the mixtures

Framing Cutting-Edge Integrative Deep-Sea Biodiversity Monitoring via Environmental DNA and Optoacoustic Augmented Infrastructures

Deep-sea ecosystems are reservoirs of biodiversity that are largely unexplored, but their exploration and biodiscovery are becoming a reality thanks to biotechnological advances (e.g., omics technologies) and their integration in an expanding network of marine infrastructures for the exploration of the seas, such as cabled observatories. While still in its infancy, the application of environmental DNA (eDNA) metabarcoding approaches is revolutionizing marine biodiversity monitoring capability. Indeed, the analysis of eDNA in conjunction with the collection of multidisciplinary optoacoustic and environmental data, can provide a more comprehensive monitoring of deep-sea biodiversity. Here, we describe the potential for acquiring eDNA as a core component for the expanding ecological monitoring capabilities through cabled observatories and their docked Internet Operated Vehicles (IOVs), such as crawlers. Furthermore, we provide a critical overview of four areas of development: (i) Integrating eDNA with optoacoustic imaging; (ii) Development of eDNA repositories and cross-linking with other biodiversity databases; (iii) Artificial Intelligence for eDNA analyses and integration with imaging data; and (iv) Benefits of eDNA augmented observatories for the conservation and sustainable management of deep-sea biodiversity. Finally, we discuss the technical limitations and recommendations for future eDNA monitoring of the deep-sea. It is hoped that this review will frame the future direction of an exciting journey of biodiscovery in remote and yet vulnerable areas of our planet, with the overall aim to understand deep-sea biodiversity and hence manage and protect vital marine resources

Domain Walls and Anchoring Transitions Mimicking Nematic Biaxiality in the Oxadiazole Bent-Core Liquid Crystal C7

We investigate the origin of secondary disclinations that were recently described as a new evidence of a biaxial nematic phase in an oxadiazole bent-core thermotropic liquid crystal C7. With 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 an uniaxial nematic 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 bonding plates. The domain walls can be easily removed by applying a modest 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 tangential-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. The study shows that C7 exhibits only a uniaxial nematic phase and demonstrate yet another mechanism (formation of secondary disclinations) by which a uniaxial nematic can mimic a biaxial nematic behaviour.Comment: 21 pages, 9 Figures, 1 Tabl

AMIRA P521 progress report for March to October '98: Relationship between hydrodynamics and Gibbsite precipitation

Abstract not available

The influence of Fe-oxides and organic matter on surface properties of nanostructured microaggregates of the Terra rossa and Calcocambisol

This study investigates the influence of Fe-oxides and organic matter on surface properties of nanostructured mineral microaggregates obtained from the terra rossa and calcocambisol developed on hard limestone and dolomite in Istria, Croatia. The mineral composition and the morphology of samples were investigated using X-ray diffraction and field emission scanning electron microscope (FE-SEM), respectively. In order to determine the influence of Fe-oxides and organic matter coatings on surface properties of soils, samples were selectively dissolved. Particle size distribution, specific surface area (SSA) and electrophoretic mobility (EPM) were measured on the following soil subsamples: original samples, samples treated with H2O2, samples treated with H2O2+NH4-oxalate and samples treated with H2O2+NH4-oxalate+Na-dithionite-citrate-bicarbonate. The obtained results showed that kaolinites (kaolinites which form intercalation compounds with DMSO-KlD and kaolinites which do not intercalate with DMSO-Kl) (RANGE et al., 1969), illitic material (ŚRODOŃ, 1984 ; ŚRODOŃ & EBERL, 1984) and Fe-oxides are the main mineral components in the clay fraction of the terra rossa. Calcocambisol enriched in organic matter contains kaolinites, chlorite and vermiculite as main mineral phases. The main differences in surface properties between the terra rossa and calcocambisol was a consequence of diverse particle-size distribution, mineral composition and the share of organic matter. FE-SEM analysis of the terra rossa and calcocambisol samples after removal of amorphous Fe-oxides and organic matter shows disintegration. This disintegration is evident in reducing particle size from 2 µm to 50 nm for the terra rossa and from 1.8 µm to 50 nm for calcocambisol, respectively. Kaolinite with particle size about 50 nm shows pseudohexagonal form in analysed soils. The SSA increased proportionally to the amount of the removed organic matter in both soils. After the removal of well-crystallized Fe-oxides the SSA slightly decreased in calcocambisol and significantly increased in the terra rossa due to major soil microaggregate decomposition. EPM measurements of investigated samples were diverse

The influence of Fe-oxides and organic matter on surface properties of nanostructured microaggregates of the Terra rossa and Calcocambisol

This study investigates the influence of Fe-oxides and organic matter on surface properties of nanostructured mineral microaggregates obtained from the terra rossa and calcocambisol developed on hard limestone and dolomite in Istria, Croatia. The mineral composition and the morphology of samples were investigated using X-ray diffraction and field emission scanning electron microscope (FE-SEM), respectively. In order to determine the influence of Fe-oxides and organic matter coatings on surface properties of soils, samples were selectively dissolved. Particle size distribution, specific surface area (SSA) and electrophoretic mobility (EPM) were measured on the following soil subsamples: original samples, samples treated with H2O2, samples treated with H2O2+NH4-oxalate and samples treated with H2O2+NH4-oxalate+Na-dithionite-citrate-bicarbonate. The obtained results showed that kaolinites (kaolinites which form intercalation compounds with DMSO-KlD and kaolinites which do not intercalate with DMSO-Kl) (RANGE et al., 1969), illitic material (ŚRODOŃ, 1984 ; ŚRODOŃ & EBERL, 1984) and Fe-oxides are the main mineral components in the clay fraction of the terra rossa. Calcocambisol enriched in organic matter contains kaolinites, chlorite and vermiculite as main mineral phases. The main differences in surface properties between the terra rossa and calcocambisol was a consequence of diverse particle-size distribution, mineral composition and the share of organic matter. FE-SEM analysis of the terra rossa and calcocambisol samples after removal of amorphous Fe-oxides and organic matter shows disintegration. This disintegration is evident in reducing particle size from 2 µm to 50 nm for the terra rossa and from 1.8 µm to 50 nm for calcocambisol, respectively. Kaolinite with particle size about 50 nm shows pseudohexagonal form in analysed soils. The SSA increased proportionally to the amount of the removed organic matter in both soils. After the removal of well-crystallized Fe-oxides the SSA slightly decreased in calcocambisol and significantly increased in the terra rossa due to major soil microaggregate decomposition. EPM measurements of investigated samples were diverse