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Aims. Through the ATOMIUM project, based on an ALMA large program, we aim to present a consistent view of a sample of 17 nearby cool evolved stars (Aymptotic Giant Branch and red supergiant stars). Methods. Here we present VLT/SPHERE-ZIMPOL polarimetric maps obtained in the visible of 14 out of the 17 ATOMIUM sources. They were obtained contemporaneously with the ALMA high spatial resolution data. To help interpret the polarized signal, we produced synthetic maps of light scattering by dust, through 3D radiative transfer simulations with the RADMC3D code. Results. The degree of linear polarization (DoLP) observed by ZIMPOL spreads across several optical filters. We infer that it primarily probes dust located just outside of the point spread function, and in or near the plane of the sky, with a total optical depth close to unity in the line of sight, representing only a fraction of the total circumstellar dust. The maximum DoLP ranges from 0.03-0.38 depending on the source, fractions that can be reproduced by our 3D pilot models for grains composed of common dust species. The spatial structure of the DoLP shows a diverse set of shapes. Only for three sources do we note a correlation between the ALMA CO and SiO lines, which trace the gas density, and the DoLP, which traces the dust. Conclusion. The clumpiness of the DoLP and the lack of a consistent correlation between the gas and the dust location show that, in the inner circumstellar environment (CSE), dust formation occurs at very specific sites. This has potential consequences for the derived mass-loss rates and dust-to-gas ratio in the inner region of the CSE. Except for $\pi^1$~Gru and perhaps GY Aql, we do not detect interactions between the circumstellar wind and the hypothesized companions that shape the wind at larger scales. This suggests that the orbits of any other companions are tilted out of the plane of the sky., Comment: Accepted for publication in Astronomy & Astrophysics. 22 pages, 15 figures, 5 tables

By imitating natural water circulation, artificial water generation processes can produce clean water by utilizing readily available and inexhaustible solar energy. Such a process can address the current global crises related to both energy and water shortages, and expand currently available water resources from rivers, ground water and ice to seawater, brackish water and atmospheric humidity. Among the many materials used for water generation, aerogels offer a great potential due to the inherent combination of three-dimensional, monolithic structure and porous, interconnected network. In this article, we review aerogel-based water generation from brine and atmospheric water. The unique features of aerogels are elucidated from the viewpoint of photo-thermal conversion and water transport. These two components are necessary to achieve efficient solar-driven water production systems. In addition to describing the material specifications, this paper reviews a diversity of structural designs that aim to improve the evaporation performance, including the assembly strategy of light absorption and thermal insulation layers, the reduction of evaporation enthalpy, and the salt-rejection control, as well as Marangoni effect. After evaluating different types of solar-powered water utilization technologies, the paper ends with the challenges for the commercialization and widespread use of aerogel-based water production systems: their disconnect from the current aerogel industry, high production cost and weak mechanical properties, and a lack of standardized performance testing, as well as our future perspective for their application opportunities., Materials Science and Engineering: R, 154, ISSN:0927-796X, ISSN:1879-212X

Aerogels were listed among the top ten emerging technologies in chemistry by IUPAC in 2022. Their record-breaking properties sparked the emergence of a thriving insulation market, but solutions are sought to promote additional applications. A 3D assembly process based on direct ink writing of "aerogel-in-aerogel" nanocomposites is presented. The printed polyimide-silica aerogels are non-brittle (E = 6.7 MPa) with a super-insulating thermal conductivity (20.3 mW m(-1) K-1) and high thermal stability (T-5wt% 447 degrees C). In addition, they display excellent low-loss dielectric properties and microwave transmission over all relevant communication bands and can be functionalized for electromagnetic interference (EMI) shielding. The high shape-fidelity printing, combined with laser-induced etching of thermally conductive graphene layers, enable precise thermal management for portable electronics or maintain an extreme temperature gradient (-40 to +50 degrees C) across a millimeter-scale partition., Advanced Materials Technologies, ISSN:2365-709X

Carbon nanostructures-silica aerogel composites were synthesized and characterized to assess the effect of carbon nanotubes (CNTs) or graphene oxide (GO) on the silica aerogel properties. The sol-gel chemistry was based on methyltrimethoxysilane (MTMS) and 3-aminopropyltrimethoxysilane (APTMS) as silica precursor system, with varying amounts of APTMS (0–20% mol of Si). APTMS significantly impacted the materials' physical properties. The chemistry and microstructure were investigated by FTIR, NMR, TEM, SEM, SAXS and BET. The addition of CNTs induced the growth of the silica matrix around them; thus, an elongated shape was observed in the silica structural units. APTMS and CNTs have a synergistic effect on the mechanical properties, increasing the Young's modulus up to 14 MPa. Small amounts of carbon materials (∼1 wt%) in the MTMS-matrix improved its thermal insulation property, particularly for temperatures above 50 °C. In terms of electrochemical properties, the carbon nanostructures lead to higher specific capacitances and a reduction in resistance. The characterizations here performed allowed a better understanding of the interactions between the silica and carbon phases. The possibility to obtain materials with tailored properties demonstrates their application potential in several areas, such as thermal insulation and energy storage.

Introduction: We present the results of the COVID-19 rule-out protocol at Ghent University Hospital, a step-wise testing approach which included repeat NFS SARS-CoV-2 rRT-PCR, respiratory multiplex RT-PCR, low-dose chest CT and bronchoscopy with BAL to confirm or rule-out SARS-CoV-2 infection in patients admitted with symptoms suggestive of COVID-19. Results: Between 19 March 2020 and 30 April 2020, 455 non-critically ill patients with symptoms suspect for COVID-19 were admitted. The initial NFS for SARS-CoV-2 rRT-PCR yielded 66.9%, the second NFS 25.4% and bronchoscopy with BAL 5.9% of total COVID-19 diagnoses. In the BAL fluid, other respiratory pathogens were detected in 65% (13/20) of the COVID-19 negative patients and only in 1/7 COVID-19 positive patients. Retrospective antibody testing at the time around BAL sampling showed a positive IgA or IgG in 42.9 % of the COVID-19 positive and 10.5% of the COVID-19 negative group. Follow-up serology showed 100% COVID-19 positivity in the COVID-19 positive group and 100% IgG negativity in the COVID-19 negative group. Conclusion: In our experience, bronchoscopy with BAL can have an added value to rule-in or rule-out COVID-19 in patients with clinical and radiographical high-likelihood of COVID-19 and repeated negative NFS testing. Furthermore, culture and respiratory multiplex PCR on BAL fluid can aid to identify alternative microbial etiological agents in this group. Retrospective analysis of antibody development in this selected group of patients suggests that the implementation of serological assays in the routine testing protocol will decrease the need for invasive procedures like bronchoscopy.

Radiative transfer is a notoriously difficult and computationally demanding problem. Yet, it is an indispensable ingredient in nearly all astrophysical and cosmological simulations. Choosing an appropriate discretization scheme is a crucial part of the simulation, since it not only determines the direct memory cost of the model but also largely determines the computational cost and the achievable accuracy. In this paper, we show how an appropriate choice of directional discretization scheme as well as spatial model mesh can help alleviate the computational cost, while largely retaining the accuracy. First, we discuss the adaptive ray-tracing scheme implemented in our 3D radiative transfer library Magritte, that adapts the rays to the spatial mesh and uses a hierarchical directional discretization based on HEALPix. Second, we demonstrate how the free and open-source software library Gmsh can be used to generate high quality meshes that can be easily tailored for Magritte. In particular, we show how the local element size distribution of the mesh can be used to optimise the sampling of both analytically and numerically defined models. Furthermore, we show that when using the output of hydrodynamics simulations as input for a radiative transfer simulation, the number of elements in the input model can often be reduced by an order of magnitude, without significant loss of accuracy in the radiation field. We demonstrate this for two models based on a hierarchical octree mesh resulting from adaptive mesh refinement (AMR), as well as two models based on smoothed-particle hydrodynamics (SPH) data., Comment: 12 pages, published in MNRAS

Owing to their ultralow thermal conductivity and open pore structure1-3, silica aerogels are widely used in thermal insulation4,5, catalysis6, physics7,8, environmental remediation6,9, optical devices10 and hypervelocity particle capture11. Thermal insulation is by far the largest market for silica aerogels, which are ideal materials when space is limited. One drawback of silica aerogels is their brittleness. Fibre reinforcement and binders can be used to overcome this for large-volume applications in building and industrial insulation5,12, but their poor machinability, combined with the difficulty of precisely casting small objects, limits the miniaturization potential of silica aerogels. Additive manufacturing provides an alternative route to miniaturization, but was "considered not feasible for silica aerogel"13. Here we present a direct ink writing protocol to create miniaturized silica aerogel objects from a slurry of silica aerogel powder in a dilute silica nanoparticle suspension (sol). The inks exhibit shear-thinning behaviour, owing to the high volume fraction of gel particles. As a result, they flow easily through the nozzle during printing, but their viscosity increases rapidly after printing, ensuring that the printed objects retain their shape. After printing, the silica sol is gelled in an ammonia atmosphere to enable subsequent processing into aerogels. The printed aerogel objects are pure silica and retain the high specific surface area (751 square metres per gram) and ultralow thermal conductivity (15.9 milliwatts per metre per kelvin) typical of silica aerogels. Furthermore, we demonstrate the ease with which functional nanoparticles can be incorporated. The printed silica aerogel objects can be used for thermal management, as miniaturized gas pumps and to degrade volatile organic compounds, illustrating the potential of our protocol.

Biopolymer aerogels are an emerging class of materials with potential applications in drug delivery, thermal insulation, separation, and filtration. Chitosan is of particular interest as a sustainable, biocompatible, and abundant raw material. Here, we present urea-modified chitosan aerogels with a high surface area and excellent thermal and mechanical properties. The irreversible gelation of an acidic chitosan solution is triggered by the thermal decomposition of urea at 80 °C through an increase in pH and, more importantly, the formation of abundant ureido terminal groups. The hydrogels are dried using either supercritical CO2 drying (SCD) or ambient pressure drying (APD) methods to elucidate the influence of the drying process on the final aerogel properties. The hydrogels are exchanged into ethanol prior to SCD, and into ethanol and then heptane prior to APD. The surface chemistry and microstructure are monitored by solid-state NMR and Fourier transform infrared spectroscopy, scanning electron microscopy, and nitrogen sorption. Surprisingly, large monolithic aerogel plates (70 × 70 mm2) can be produced by APD, albeit at a somewhat higher density (0.17-0.42 g/cm3). The as prepared aerogels have thermal conductivities of ∼24 and ∼31 mW/(m·K) and surface areas of 160-170 and 85-230 m2/g, for SCD and APD, respectively. For a primarily biopolymer-based material, these aerogels are exceptionally stable at elevated temperature (TGA) and char and self-extinguish after direct flame exposure. The urea-modified chitosan aerogels display superior mechanical properties compared to traditional silica aerogels, with no brittle rupture up to at least 80% strain, and depending on the chitosan concentration, relatively high E-moduli (1.0-11.6 MPa), and stress at 80% strain values (σ80 of 3.5-17.9 MPa). Remarkably, the aerogel monoliths can be shaped and machined with standard tools, for example, drilling and sawing. This first demonstration to produce monolithic and machinable, mesoporous aerogels from bio-sourced, renewable, and nontoxic precursors, combined with the potential for reduced production cost by means of simple APD, opens up new opportunities for biopolymer aerogel applications and marks an important step toward commercialization of biopolymer aerogels.

The study of quartz and other silica systems under pressure is one of the most prolific domains of research over the past 50 years because of their applications in material science and fundamental relevance to planetary interiors. The characterization of the amorphous state is essential for the comprehension of pressure-induced amorphization of minerals, the metamorphism observed in shocked materials, and the study of melt structures under pressure. Here, we measured in situ, under static compression the density, sound velocities, and electronic structure of quartz as it passes through its pressure-induced amorphization transition. The transition pressure could be derived from the abrupt increase in density and sound velocity at 24 GPa, and from strong changes in the silicon L2,3 edge and oxygen K edge between 22 and 27 GPa observed in x-ray Raman scattering data, confirming previous results from x-ray diffraction. Above this pressure, our data show an anomalous behavior in density, sound velocity, and electronic fine structure compared to the cold compressed glass and other silica polymorphs. The pressure-induced amorphous quartz has a lower density relative to that of the compressed glass, consistent with the lower average coordination inferred from a different signature in the Si L2,3 and O K electronic absorption edges measured by x-ray Raman scattering spectroscopy. This behavior sheds light on the pressure limit of tetrahedral units in SiO2 components and the existence of polyamorphism in network-forming materials, and highlights the possibility to discriminate between different amorphous states with x-ray Raman scattering spectroscopy.

Cellulose aerogels are potential alternatives to silica aerogels with advantages in cost, sustainability and mechanical properties. However, the density dependence of thermal conductivity (λ) for cellulose aerogels remains controversial. Cellulose aerogels were produced by gas-phase pH induced gelation of TEMPO-oxidized cellulose nanofibers (CNF) and supercritical drying. Their properties are evaluated by varying the CNF concentration (5–33 mg·cm−3) and by uniaxial compression (9–115 mg·cm−3). The aerogels are transparent with specific surface areas of ~400 m2·g−1, mesopore volumes of ~2 cm3·g−1 and a power-law dependence of the E-modulus (α ~ 1.53, and the highest reported E of ~1 MPa). The dataset confirms that λ displays a traditional U-shaped density dependence with a minimum of 18 mW·m−1·K−1 at 0.065 g·cm−3. For a given density, λ is ~5 mW·m−1·K−1 lower for compressed aerogels due to the alignment of nanofibers, confirmed by small angle X-ray scattering (SAXS)., Carbohydrate Polymers, 292, ISSN:0144-8617, ISSN:1879-1344

This overview paper presentsATOMIUM, a Large Programme in Cycle 6 with the Atacama Large Millimeter/submillimeter Array (ALMA). The goal ofATOMIUMis to understand the dynamics and the gas phase and dust formation chemistry in the winds of evolved asymptotic giant branch (AGB) and red supergiant (RSG) stars. A more general aim is to identify chemical processes applicable to other astrophysical environments. Seventeen oxygen-rich AGB and RSG stars spanning a range in (circum)stellar parameters and evolutionary phases were observed in a homogeneous observing strategy allowing for an unambiguous comparison. Data were obtained between 213.83 and 269.71 GHz at high (∼0″​​.025–0″​​.050), medium (∼0″​​.13–0″​​.24), and low (∼1″) angular resolution. The sensitivity per ∼1.3 km s−1channel was 1.5–5 mJy beam−1, and the line-free channels were used to image the millimetre wave continuum. Our primary molecules for studying the gas dynamics and dust formation are CO, SiO, AlO, AlOH, TiO, TiO2, and HCN; secondary molecules include SO, SO2, SiS, CS, H2O, and NaCl. The scientific motivation, survey design, sample properties, data reduction, and an overview of the data products are described. In addition, we highlight one scientific result – the wind kinematics of theATOMIUMsources. Our analysis suggests that theATOMIUMsources often have a slow wind acceleration, and a fraction of the gas reaches a velocity which can be up to a factor of two times larger than previously reported terminal velocities assuming isotropic expansion. Moreover, the wind kinematic profiles establish that the radial velocity described by the momentum equation for a spherical wind structure cannot capture the complexity of the velocity field. In fifteen sources, some molecular transitions other than12COv = 0J = 2 − 1 reach a higher outflow velocity, with a spatial emission zone that is often greater than 30 stellar radii, but much less than the extent of CO. We propose that a binary interaction with a (sub)stellar companion may (partly) explain the non-monotonic behaviour of the projected velocity field. TheATOMIUMdata hence provide a crucial benchmark for the wind dynamics of evolved stars in single and binary star models.

S-type asymptotic giant branch (AGB) stars are thought to be intermediates in the evolution of oxygen- to carbon-rich AGB stars. The chemical compositions of their circumstellar envelopes are also intermediate, but have not been studied in as much detail as their carbon- and oxygen-rich counterparts. We aim to determine the abundances of AlCl and AlF from rotational lines, which have been observed for the first time towards an S-type AGB star, W Aql. In combination with models based on PACS observations, we aim to update our chemical kinetics network based on these results. We analyse ALMA observations towards W Aql of AlCl in the ground and first two vibrationally excited states and AlF in the ground vibrational state. Using radiative transfer models, we determine the abundances and spatial abundance distributions of Al$^{35}$Cl, Al$^{37}$Cl, and AlF. We also model HCl and HF emission and compare these models to PACS spectra to constrain the abundances of these species. AlCl is found in clumps very close to the star, with emission confined within 0.1$^{\prime\prime}$ of the star. AlF emission is more extended, with faint emission extending 0.2$^{\prime\prime}$ to 0.6$^{\prime\prime}$ from the continuum peak. We find peak abundances, relative to H$_2$, of $1.7\times 10^{-7}$ for Al$^{35}$Cl, $7\times 10^{-8}$ for Al$^{37}$Cl and $1\times 10^{-7}$ for AlF. From the PACS spectra, we find abundances of $9.7\times 10^{-8}$ and $\leq 10^{-8}$, relative to H$_2$, for HCl and HF, respectively. The AlF abundance exceeds the solar F abundance, indicating that fluorine synthesised in the AGB star has already been dredged up to the surface of the star and ejected into the circumstellar envelope. From our analysis of chemical reactions in the wind, we conclude that AlF may participate in the dust formation process, but we cannot fully explain the rapid depletion of AlCl seen in the wind., Accepted for publication in Astronomy & Astrophysics

Aerogels are mesoporous materials with a rapidly growing thermal insulation market interest, partly because ambient pressure drying (APD) reduces cost. Silica gels must be hydrophobized to prevent condensation reactions and irreversible shrinkage during APD. Here, we study how hydrophobization with mono-, di-, and trifunctional organoalkoxysilanes (M, D, T) and their mixtures, affects spring-back, density, surface area, pore size and hydrophobicity. All aerogels were synthesized from a polyethoxydisiloxane precursor prepared from a tetraalkoxysilane (tetraethoxysilane, TEOS). Aged gels, hydrophobized with trimethylethoxysilane (M100), display the highest spring-back and lowest density (0.100 g/cm3) upon APD drying. Hydrophobization with pure dimethyldiethoxysilane (D100) or methyltriethoxysilane (T100) leads to excessive shrinkage and respective densities of 0.440 and 1.450 g/cm3 due to the self-polymerization from the di- and trifunctional silanes: in the D100 material, the formation of polydimethyldisiloxane (PDMS) is evident in the 29Si NMR spectra, whereas 3D silica structures (beads) are apparent for the T100 sample. Aerogels hydrophobized with binary and ternary mixtures of M, D and T display systematic variations in density: nearly constant (

Silica aerogels display an ultra-low thermal conductivity (λ) and are used as thermal superinsulators. Here, we study the influence of aging and drying processes on the microstructure and thermal conductivity of fiber-reinforced silica aerogel composites. Glass wool-silica gel composites were aged for variable times, hydrophobized, and dried either at ambient pressure or from supercritical CO2 (scCO2). The X-ray micro-tomographic data display three distinct phases: silica aerogel, glass fibers, and macroscopic pores and cracks. The silica aerogel appears as a continuous medium in the tomograms because the spatial resolution (6–11 μm) is insufficient to resolve the aerogel mesopores (∼0.02–0.10 μm). For the composites prepared by ambient pressure drying, insufficient aging led to prominent drying shrinkage and cracking, and a high macro-porosity, as quantified by 3D image analysis. Insufficient aging also led to an increase in λ from 15.7 to 21.5 mW m−1 K−1. On the contrary, composites that were nearly free of cracks and displayed a constant λ of 16.3 ± 0.8 mW m−1 K−1 could be prepared by scCO2, independent of aging time. The thermal conductivity was reproduced from the macro-porosity to within 0.7 mW m−1 K−1 using simple thermal transport models consisting of thermal elements connected in series or parallel. Our results illustrate the usefulness of X-ray micro-tomography to quantify the 3D microstructure and its effects on the bulk composite properties and the data highlight the importance of aging for the production of low λ aerogel-fiber composites by ambient pressure drying.

Tannin-silica hybrid materials are expected to feature excellent mechanic-chemical stability, large surface areas, high porosity and possess, after carbothermal reduction, high thermal stability as well as high thermal conductivity. Typically, a commercially available tetraethoxysilane is used, but in this study, a more sustainable route was developed by using a glycol-based silica precursor, tetrakis(2-hydroxyethyl)orthosilicate (EGMS), which is highly water-soluble. In order to produce highly porous, homogeneous hybrid tannin-silica aerogels in a one-pot approach, a suitable crosslinker has to be used. It was found that an aldehyde-functionalized silane (triethoxysilylbutyraldehyde) enables the covalent bonding of tannin and silica. Solely by altering the processing parameters, distinctly different tannin-silica hybrid material properties could be achieved. In particular, the amount of crosslinker is a significant factor with respect to altering the materials’ properties, e.g., the specific surface area. Notably, 5 wt% of crosslinker presents an optimal percentage to obtain a sustainable tannin-silica hybrid system with high specific surface areas of roughly 800–900 m2 g−1 as well as a high mesopore volume. The synthesized tannin-silica hybrid aerogels permit the usage as green precursor for silicon carbide materials.

The late evolutionary stages of low- and intermediate-mass stars are characterised by mass loss through a dust-driven stellar wind. Recent observations reveal complex structures within these winds, that are believed to be formed primarily via interaction with a companion. How these complexities arise, and which structures are formed in which type of systems, is still poorly understood. Particularly, there is a lack of studies investigating the structure formation in eccentric systems. We aim to improve our understanding of the wind morphology of eccentric AGB binary systems by investigating the mechanism responsible for the different small-scale structures and global morphologies that arise in a polytropic wind with different velocities. Using the smoothed particle hydrodynamics (SPH) code Phantom, we generate nine different high-resolution, 3D simulations of an AGB star with a solar-mass companion with various wind velocity and eccentricity combinations. The models assume a polytropic gas, with no additional cooling. We conclude that for models with a high wind velocity, the short interaction with the companion results in a regular spiral morphology, that is flattened. In the case of a lower wind velocity, the stronger interaction results in the formation of a high-energy region and bow-shock structure that can shape the wind into an irregular morphology if instabilities arise. High-eccentricity models show a complex, phase-dependent interaction leading to wind structures that are irregular in three dimensions. However, the significant interaction with the companion compresses matter into an equatorial density enhancement, irrespective of eccentricity., Comment: 23 pages, 22 figures

Here, we report the gelation and supercritical drying of ethanol-based silica-resorcinol-melamine-formaldehyde (RMF) composite aerogels with relative concentrations of initial reagents ranging from neat silica to neat RMF alcogels. The as-prepared materials are subsequently supercritically dried with carbon dioxide. Their properties include a thermal conductivity in the 15-20 mW·m

Silica aerogel is the ultimate thermal insulator thanks to its record-breaking low thermal conductivity (λ), open porosity and hydrophobicity. Silica aerogel's thermal conductivity is lowest at intermediate densities (ρ ≈ 0.11 g/cm ) and, because of the strong, power-law dependence of the E modulus on density, this rather low density so far led to low E moduli. Even with polymer reinforcement, increasing stiffness is only possible at higher density, thus higher conductivity. This paper explores the synthesis of silica aerogel granules using ambient pressure drying to provide enhanced mechanical stiffness whilst maintaining thermal conductivities well below 20 mW m K . The aging and drying conditions affect the interplay between mechanical and thermal properties, and are varied to optimize the physical properties. The dense (ρ≤0.29 g/cm ), but superinsulating (λ≈15 mW m K ) silica aerogels presented in this paper challenge the community's understanding of heat transport in aerogels, and do not rely on polymer reinforcement. The underlying microscopic structural parameters affecting the mechanical and thermal transport properties are investigated by modelling and simulation of the aerogel back-bone. Short aging times reduce the cross-section of, and heat transport through, inter-particle necks, leading to an overall decrease in thermal conductivity through the solid skeleton (λ ). In addition, short-aged gels undergo a partial pore collapse during ambient pressure drying of the pore fluid due to less aged, hence weaker network structures. The resulting denser structure contains additional point contacts that increase stiffness, by up to an order of magnitude. However, heat transport through these newly formed point-contacts is limited and the gas phase conduction (λ ) is further suppressed due to the even smaller pore sizes. Strong and superinsulating particles are ideal fillers for aerogel composites, concrete and renders. The optimized APD aerogels, available as granules, are finally compiled in a composite thermal insulation board with an effective thermal conductivity down to 20 mW m K with improved strength: a 2-fold increase for E, compared to a board produced from classical silica aerogel granulate. The possibility to improve mechanical properties of pure silica aerogels can help aerogels to break into new high-strength, superinsulating structural applications needed to reduce carbon emissions of the built environment., Acta Materialia, 213, ISSN:1359-6454

Asymptotic giant branch (AGB) stars are known to lose a significant amount of mass by a stellar wind, which controls the remainder of their stellar lifetime. High angular-resolution observations show that the winds of these cool stars typically exhibit mid- to small-scale density perturbations such as spirals and arcs, believed to be caused by the gravitational interaction with a (sub-)stellar companion. We aim to explore the effects of the wind-companion interaction on the 3D density and velocity distribution of the wind, as a function of three key parameters: wind velocity, binary separation and companion mass. For the first time, we compare the impact on the outflow of a planetary companion to that of a stellar companion. We intend to devise a morphology classification scheme based on a singular parameter. With our grid of models we cover the prominent morphology changes in a companion-perturbed AGB outflow: slow winds with a close, massive binary companion show a more complex morphology. Additionally, we prove that massive planets are able to significantly impact the density structure of an AGB wind. We find that the interaction with a companion affects the terminal velocity of the wind, which can be explained by the gravitational slingshot mechanism. We distinguish between two types of wind focussing to the orbital plane resulting from distinct mechanisms: global flattening of the outflow as a result of the AGB star's orbital motion and the formation of an EDE as a consequence of the companion's gravitational pull. We investigate different morphology classification schemes and uncover that the ratio of the gravitational potential energy density of the companion to the kinetic energy density of the AGB outflow yields a robust classification parameter for the models presented in this paper., 19 pages, 11 figures

Evolved low- to intermediate-mass stars are known to shed their gaseous envelope into a large, dusty, molecule-rich circumstellar nebula which typically develops a high degree of structural complexity. Most of the large-scale, spatially correlated structures in the nebula are thought to originate from the interaction of the stellar wind with a companion. As part of the Atomium large programme, we observed the M-type asymptotic giant branch (AGB) star R Hydrae with ALMA. The morphology of the inner wind of R Hya, which has a known companion at ~3500 au, was determined from maps of CO and SiO obtained at high angular resolution. A map of the CO emission reveals a multi-layered structure consisting of a large elliptical feature at an angular scale of ~10'' that is oriented along the north-south axis. The wind morphology within the elliptical feature is dominated by two hollow bubbles. The bubbles are on opposite sides of the AGB star and lie along an axis with a position angle of ~115 deg. Both bubbles are offset from the central star, and their appearance in the SiO channel maps indicates that they might be shock waves travelling through the AGB wind. An estimate of the dynamical age of the bubbles yields an age of the order of 100 yr, which is in agreement with the previously proposed elapsed time since the star last underwent a thermal pulse. When the CO and SiO emission is examined on subarcsecond angular scales, there is evidence for an inclined, differentially rotating equatorial density enhancement, strongly suggesting the presence of a second nearby companion. The position angle of the major axis of this disc is ~70 deg in the plane of the sky. We tentatively estimate that a lower limit on the mass of the nearby companion is ~0.65 Msol on the basis of the highest measured speeds in the disc and the location of its inner rim at ~6 au from the AGB star., 21 pages, 23 figures

Available data suggests that granulated aerogels can be of interest in terms of their sound absorption performance in the audio frequency range. However, there is still no thorough understanding of the complex physical phenomena which are responsible for their observed acoustical properties. This work is an attempt to address this gap through advanced material characterization methods and mathematical modelling. Aerogel samples are produced through a two-step, acid-base sol-gel process, with sol silica concentration and density being the main variables. Their pore structure is carefully characterized by nitrogen sorption analysis and scanning electron microscopy. The acoustical properties of hard-backed granular silica aerogels are measured in an impedance tube and the results predicted accurately with the adopted theoretical model. Although silica aerogels have over 90% of open interconnected pores, this was neither reflected in the measured acoustical properties nor the parameter values predicted with the model. Novel results show that only a proportion of the micro and mesopores in the direct vicinity of the grain surface influenced the acoustical properties of aerogels. Further work in the hierarchical pore structure of aerogels is required to better understand the roles of different pore scales on the measured acoustical properties of a granulated aerogel.

Silica aerogels are highly porous (~95%), predominantly mesoporous (20–50 nm) materials with very high surface area (~800 m2/g), but applications that valorize the chemical properties linked to the high surface area lag behind those that valorize the pore structure (thermal insulation). Here, we present widely applicable protocols to synthesize and characterize organo-functionalized silica aerogels with high surface area (356–1177 m2/g) and high mass loadings of surface functional groups (1.0–4.9 mmol/g, 0.9–3.9 molecules/nm2). Wet silica gels are soaked into dilute solutions containing pre-hydrolyzed organofunctional trialkoxysilanes, followed by supercritical CO2 drying. The retention of the various functional groups in the dry aerogels is confirmed by FTIR and their concentrations quantified by solid-state NMR spectroscopy. The mild reaction conditions are compatible with all tested functional groups (silanol, ethoxy, trimethylsilyl, amino, vinyl, methyl methacrylate, epoxy, phosphonate), without the need to optimize for each specific functional silane, making the synthesis of organofunctionalized aerogels a routine task.

Supercritical drying is widely considered as the gold standard to produce aerogels that preserve the microstructure of the gels, but we have found this is not always the case. Chitosan aerogel, one of the emerging biopolymer aerogels, was prepared by chemical cross-linking gelation, followed by solvent exchange with methanol and supercritical drying using CO2. Small-angle X-ray scattering analysis shows that the structure of the wet gel, which consists of Gaussian chains of individual molecular strands, converts into a nanofibrous network during CO2 processing. In situ observation reveals a drastic shrinkage of the gel in CO2, demonstrating that physical coagulation caused by the low affinity between chitosan and CO2 is the main structure-forming step. These results challenge the common perception of supercritical drying: it is no longer an inactive drying method, but rather an active nanostructure forming a tool to produce porous biopolymer materials with tailored structure and properties.

Aldehyde-free, transparent chitosan aerogel is reported. The aerogel was prepared by thermal decomposition of urea to induce gelation of a chitosan solution, followed by solvent exchange to ethanol, and supercritical drying. Low urea concentrations (≤ 25 g L-1) result in transparent and highly mesoporous aerogels, while higher urea concentrations (≥ 30 g L-1) produce opaque, more macroporous aerogels. The high surface areas of > 400 m2 g-1, large mesopore volumes up to 3.5 cm3 g-1, and optical transparency of the low-urea aerogels indicate a high structural homogeneity at the mesoscale, and the properties comparable to previously reported transparent chitosan aerogels prepared with formaldehyde crosslinking. The macroscopic size changes of the wet gels indicate that microstructure formation is controlled by the timing of chitosan coagulation, which depends among others on urea concentration. The aldehyde-free, microstructure-tunable process provides a new series of transparent biopolymer aerogels with "true aerogel" mesoporous structures.

The functionality of biopolymer aerogels is inherently linked to its microstructure, which in turn depends on the synthesis protocol. Detailed investigations on the macroscopic size change and nanostructure formation during chitosan aerogel synthesis reveal a new aspect of biopolymer aerogels that increases process flexibility. Formaldehyde-cross-linked chitosan gels retain a significant fraction of their original volume after solvent exchange into methanol (50.3 %), ethanol (47.1 %) or isopropanol (26.7 %), but shrink dramatically during subsequent supercritical CO

Silica aerogel is the archetypal thermal superinsulator and commonly applied to improve the thermal performance of on- and off-shore industrial infrastructure and buildings. Hitherto, the main products on the market are silica aerogel based blankets fabricated by casting a silica sol into a porous or fiber matrix, followed by gelation, hydrophobization, and (supercritical) drying. Considering the diffusion efficiency of the reagents and solvents used in the preparation, a reduced size of the gel bodies may accelerate and simplify the sol-gel, hydrophobization, and drying processes. Thus, particle based products, derived from silica aerogel granulate and powder additives and semi-finished products, are an attractive solution towards inexpensive aerogel applications. Here, we optimized the process parameters for silica aerogel powder production from three common silica precursors: waterglass (WG), ion-exchanged waterglass, and tetraethoxysilane (TEOS), including gelation pH, hydrophobization procedure, solvent system, processing temperatures, and ambient pressure drying protocol. Successful hydrophobization is confirmed by elemental analysis, FTIR and quantitative solid-state NMR spectroscopy. All three routes lead to silica aerogel powders with similar type IV isotherms, and BET surface areas above 700 m2/g. Importantly, the thermal conductivity of the packed powder beds does not exceed 20 mW/(m⋅K) for all three routes, implying even lower thermal conductivities of the aerogel phase itself. Total processing time, including gelation, aging, surface modification, and ambient pressure drying is between 2 and 4 h, depending on the selected route. Given that high quality silica aerogel powders can be produced from all investigated silica precursors and hydrophobization agents, the process selection for industrial upscaling can be based entirely on engineering and economic considerations.

Chitosan is an abundant biopolymer derived from food waste with attractive properties, particularly its high biocompatibility and easy chemical processability. Here, we review the rapidly expanding literature on chitosan-based porous materials with a focus on the gelation mechanisms, the three-dimensional multiscale structural control, and the diverse chemical functionality not accessible by other biopolymers. The properties vary widely: from supercritically dried, mesoporous chitosan aerogels to very light, freeze-dried macroporous scaffolds. Porous chitosan displays impressive performance at the laboratory scale, but the highly (meso)porous nature amplifies not only the beneficial functionality of chitosan, but also its drawbacks, resulting in serious barriers to industrialization. In order to facilitate technology transfer, we critically discuss the practical feasibility of chitosan aerogels in potential applications compared to conventional and other biopolymer-based porous or nonporous materials.

Freeze-dried nanofibrous scaffolds are flexible, but typically have high thermal conductivities. Conversely, silica aerogel has an ultra-low thermal conductivity, but is brittle. Here, the impregnation of pullulan/PVA nanofiber scaffolds with hydrophobic silica aerogel decreased the thermal conductivity from 31.4 to 17.7 mW/(m·K). The compatibility between the silylated nanofibers and the silica aerogel promotes the overgrowth of silica particles onto the fiber surfaces and the fiber incorporation. The composites display improved compressive and tensile properties compared to the neat pullulan scaffold and silica aerogel. The composite's E-modulus is 234 kPa compared to 4 kPa for the pullulan scaffold and 102 kPa for the silica aerogel. The composite's tensile strength is five times higher than that of the silica aerogel. Because of its reduced brittleness, the pullulan-silica aerogel composites can be shaped using a sharp blade. The composites can sustain uniaxial compression up to 80% strain, but the decompressed composites display two times higher densities because the strain is partially irreversible. This densification reduces thermal conductivity to 16.3 mW/(m·K) and increases final compressive strength by a factor of seven. Both the as prepared and densified composites demonstrate unique material properties in terms of thermal conductivity, mechanical strength and machinability. Keywords: Nanocomposite, Polysaccharide, Nanofibers, Hybrid aerogels, Densification

Silica aerogel is a promising candidate for improving the mechanical properties of epoxy-based nanocomposites due to the unique properties such as the 3-dimensional nanoporous structure and high surface area. In this study rheological, mechanical and thermal properties of the silica aerogel-epoxy nanocomposites were investigated. The rheological results demonstrated an increase in viscosity of the nanocomposite suspension compared to the neat resin. The results of dynamic mechanical along with the thermal analysis showed that the addition of 6 wt% of silica aerogel causes the storage modulus and glass transition point (Tg) to be increased by 11% and 5 °C, respectively. Also, significant improvements in the elastic modulus (35%), tensile strength (62%) and toughness (126%) were achieved with the optimal volume fraction of silica aerogel (6 wt%). Two main fracture mechanisms were involved in the fracture behavior of the silica aerogel-epoxy nanocomposite: (a) crack pining and deflection, and (b) plastic deformation (debonding).

Polymer nanocomposites reinforced with inorganic fillers have sparked new aerospace, sports goods, automotive, and civil engineering applications. Here, epoxy nanocomposites with both hydrophobic a...

Biopolymer aerogels were among the first aerogels produced, but only in the last decade has research on biopolymer and biopolymer-composite aerogels become popular, motivated by sustainability arguments, their unique and tunable properties, and ease of functionalization. Biopolymer aerogels and open-cell foams have great potential for classical aerogel applications such as thermal insulation, as well as emerging applications in filtration, oil-water separation, CO2 capture, catalysis, and medicine. The biopolymer aerogel field today is driven forward by empirical materials discovery at the laboratory scale, but requires a firmer theoretical basis and pilot studies to close the gap to market. This Review includes a database with over 3800 biopolymer aerogel properties, evaluates the state of the biopolymer aerogel field, and critically discusses the scientific, technological, and commercial barriers to the commercialization of these exciting materials.