Aerogel Particles Research Articles

Super-Stretchable Hybrid Aerogels by Self-Templating Strategy for Cross-Media Thermal Management.

Personal thermal management (PTM) materials have attracted increasing attention owing to their application for personal comfort in an energy-saving mode. However, they normally work in the same media such as in the air, and little is known about what will happen in other media like water. In this study, a system for cross-media thermal management (CMTM): passive cooling in air and thermal insulation underwater is proposed. Hybrid aerogels comprising thermoplastic polyurethane (TPU) matrix and superhydrophobic silica aerogel particle (SSAP) for CMTM are designed and synthesized using a thermally induced phase separation and self-templating strategy. The TPU matrix endows the aerogels with super stretchability (500%), shape memory, and outstanding healing recovery rate (89.9%), which are ideal characteristics for potential wearable usage. Additionally, the TPU and SSAP endow the aerogel with high solar reflectivity and infrared emissivity, thus achieving a sub-ambient cooling of 10.6°C in air. Moreover, the SSAP endows the aerogels with low thermal conductivity (0.052 W m-1 ·K-1 ) and high hydrophobicity (143°), enabling the aerogels for underwater thermal insulation. The CMTM performance of the aerogels makes them for potential uses in cross-media environments such as reefs and islands where cooling in air and thermal insulation in water are required.

Pectin-based aerogel particles for drug delivery: Effect of pectin composition on aerogel structure and release properties

In this work, nanostructured pectin aerogels were prepared via a sol-gel process and subsequent drying under supercritical conditions. To this end, three commercially available citrus pectins and an in-house produced and enzymatically modified watermelon rind pectin (WRP) were compared. Then, the effect of pectin's structure and composition on the aerogel properties were analysed and its potential application as a delivery system was explored by impregnating them with vanillin. Results showed that the molecular weight, degree of esterification and branching degree of the pectin samples played a main role in the production of hydrogels and subsequent aerogels. The developed aerogel particles showed high specific surface areas (468–584 m2/g) and low bulk density (0.025–0.10 g/cm3). The shrinkage effect during aerogel formation was significantly affected by the pectin concentration and structure, while vanillin loading in aerogels and its release profile was also seen to be influenced by the affinity between pectin and vanillin. Furthermore, the results highlight the interest of WRP as a carrier of active compounds which might have potential application in food and biomedical areas, among others.

A facile synthesis approach of silica aero-gel/eicosane particles and its potential application on polyester fabric to impart thermoregulation properties

This article aims to study the thermo-regulating properties of infiltrated Phase change material (PCM) micro-particles treated on polyester fabric. The melt infiltration method was implemented for the synthesis of the Silica aero-gel/Eicosane particles by dispersing eicosane in silica aero-gel. Synthesized particles were incorporated into the polyester knitted fabric by both exhaustion dyeing and coating method to impart the thermoregulation characteristics. The crystalline structure and the particle size of aero-gel infiltrated PCM particles were measured by X-ray diffraction (XRD) analyzer. The presence of eicosane particles deposited on the fabric surface was confirmed by the Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscope (SEM). Finally, while the sample was subjected to heating, both the dyed and coated fabric showed resistance against the rise of temperature due to the presence of phase transition PCM micro-particles compared to the untreated raw fabric sample.

Direct magnetic sorbent sampling flame atomic absorption spectrometry (DMSS-FAAS) for highly sensitive determination of trace metals

A procedure of direct magnetic sorbent sampling in flame atomic absorption spectrometry (DMSS-FAAS) was developed in this work. Metal-loaded magnetic sorbents were directly inserted in the flame of the FAAS for direct metal desorption/atomization. Magnetic graphene oxide aerogel (M-GOA) particles were synthesized, characterized, and used as a proof-of-concept in the magnetic dispersive solid phase extraction of Pb2+ ions from water samples. M-GOA was selected because is a light and porous sorbent, with high adsorption capacity, that is quickly burned by the flame. Magnetic particles were directly inserted in the flame by using a metallic magnetic probe, thereby avoiding the need for a chemical elution step. As all the extracted Pb2+ ions arrive to the flame without passing through the nebulization system, a drastic increase in the analytical signal was achieved. The improvement in the sensitivity of the proposed method (DMSS-FAAS) for Pb2+ determination was at least 40 times higher than the conventional procedure in which the Pb2+ is extracted, eluted, and analyzed by conventional flame atomic absorption spectrometry (FAAS) via the nebulization system. The analytical curve was linear from 5.0 to 180.0 μg L−1 and the limit of detection was found to be 1.30 μg L−1. Background measurements were insignificant, and the atomic absorption peaks were narrow and reproducible. Precision assessed as a percentage of the relative standard deviation %RSD was found to be 17.4, 7.1, and 7.8% for 10, 70, and 180 μg L−1 levels, respectively. The method showed satisfactory results even in the presence of other ions (Al3+, Cr3+, Co2+, Cu2+, Fe3+, Mn2+, Ba2+, Mg2+, and Li+). The performance of the new system was also evaluated for Cd2+ ions, as well as by using other magnetic particles available in our lab: magnetic carbon nanotubes (M-CNTs), magnetic restricted access carbon nanotubes (M-RACNT), magnetic poly (methacrylic acid-co-ethylene glycol dimethacrylate) (M-PMA), magnetic nanoparticles coated with orange powder peel (M-OPP), and magnetic nanoparticles covered with SiO2 (M − SiO2). Analytical signals increased for both analytes in all sorbents (increases of about 4–37 times), attesting the high potential and applicability of the proposed method. Simplicity, high analytical frequency, high detectability and reproducibility, low cost, and possibility of being totally mechanized are the most relevant advantages.

Silica aerogel composited with both plasmonic nanoparticles and opacifiers for high-efficiency photo-thermal harvest

Plasmonic nanoparticles are doped in silica aerogels for high-efficiency photothermal conversion of solar energy in seawater desalination and so on. However, this suffers from remarkable heat loss problem via near-infrared radiation. The present work proposes a novel aerogel composited with both plasmonic nanoparticles and opacifiers. The radiative characteristics of the aerogel composite were numerically investigated by coupling the T-matrix method and Monte Carlo method. The opacifiers promote the extinction characteristics in the infrared wavelength range and reduce the radiative thermal conductivity, while the plasmonic nanoparticles enhance the absorption efficiency in the solar spectrum. Moreover, silica aerogels doped with both silver nanoparticles and indium tin oxide (ITO) particles were prepared and tested. It is found that the optimal radius and volume fraction of ITO particles are 1000 nm and 1% at 300 K, respectively, based on the silica aerogel (particle radius of 5 nm and porosity of 95%) doped with silver plasmonic nanoparticles (particle radius of 10 nm and concentration of 5%). They can achieve an absorption efficiency of 87.65% in the solar spectrum and a low transmittance in the infrared range with reduced heat loss. The present work paves a new way to design full-spectrum absorption aerogels for high-efficiency photothermal conversion.

Chitosan Aerogel Particles as Nasal Drug Delivery Systems.

The nasal drug delivery route has distinct advantages, such as high bioavailability, a rapid therapeutic effect, non-invasiveness, and ease of administration. This article presents the results of a study of the processes for obtaining chitosan aerogel particles that are promising as nasal or inhalation drug delivery systems. Obtaining chitosan aerogel particles includes the following steps: the preparation of a chitosan solution, gelation, solvent replacement, and supercritical drying. Particles of chitosan gels were obtained by spraying and homogenization. The produced chitosan aerogel particles had specific surface areas of up to 254 m2/g, pore volumes of up to 1.53 cm3/g, and porosities of up to 99%. The aerodynamic diameters of the obtained chitosan aerogel particles were calculated, the values of which ranged from 13 to 59 µm. According to the calculation results, a CS1 sample was used as a matrix for obtaining the pharmaceutical composition "chitosan aerogel-clomipramine". X-ray diffraction (XRD) analysis of the pharmaceutical composition determined the presence of clomipramine, predominantly in an amorphous form. Analysis of the high-performance liquid chromatography (HPLC) data showed that the mass loading of clomipramine was 35%. Experiments in vivo demonstrated the effectiveness of the pharmaceutical composition "chitosan aerogel-clomipramine" as carrier matrices for the targeted delivery of clomipramine by the "Nose-to-brain" mechanism of nasal administration. The maximum concentration of clomipramine in the frontal cortex and hippocampus was reached 30 min after administration.

Microstructure evolution and microwave absorbing properties of novel double-layered SiC reinforced SiO2 aerogel

In this paper, a novel double-layered SiC reinforced SiO2 aerogel (SSA) was successfully synthesized by a facile route. The porous double-layered SiC microstructure was constructed by chemical vapor deposition (CVD) technology, and SiO2 aerogel was introduced by sol-gel method to adjust the dielectric properties. The microstructures of the interconnected double-layered SiC structure remained intact after SSA formation. The porous SiO2 aerogel particles were filled between the double-layered SiC structure, and the stem segments of the double-layered SiC structure were wrapped by SiO2 aerogel. In addition, SiO2 aerogel spread into the hollow pores of the double-layered SiC, forming a large number of interfaces. As expected, SSA could be used as an absorber. The minimum reflection loss (RL) value of SSA achieved − 22.80 dB at 15.77 GHz at the thickness of 3.57 mm. The optimal effective absorption bandwidth (fE) of 6.8 GHz was recorded at a 4.0 mm absorber thickness. The absorber thickness of 3.5–5.0 mm was easy to obtain wider fE and smaller RL, which provided practical guidance for the application of SSA. Finally, the microwave absorbing mechanism of SSA was studied deeply. The importance of attenuation constant (α) was more significant than the impedance matching ratio (Zr) for the microwave absorption performance of SSA. The higher Zr ascertained that a large proportion of the electromagnetic waves entered the SSA absorber, and then the α supported the microwave absorbing mechanisms.

Preparation of Protein Aerogel Particles for the Development of Innovative Drug Delivery Systems.

The research was oriented towards the preparation of aerogel particles based on egg white and whey protein isolate using various dispersion methods: dripping, spraying, and homogenization. Based on the results of analytical studies, the most appropriate samples were selected to obtain aerogels loaded with the drug. The results of the experimental research were used to study methods for obtaining nasal drug delivery systems based on aerogels. Protein aerogels were obtained by thermal gelation followed by supercritical drying. The obtained particles of protein aerogels have a specific surface area of up to 350 m2/g with a pore volume of up to 2.9 cm3/g, as well as a porosity of up to 95%. The results of experimental studies have shown that changing the dispersion method makes it possible to control the structural characteristics of protein aerogel particles. The results of the studies were applied to obtain innovative nasal drug delivery systems for the treatment of socially significant diseases. Analytical studies were conducted to determine the amount and state of adsorbed drugs in protein aerogel particles, as well as in vivo experiments on the distribution of clomipramine in blood plasma and brain tissue of rats to study the pharmacokinetics and bioavailability of the resulting drug-loaded protein aerogel.

Flexible Electrospun strawberry-like structure SiO2 aerogel nanofibers for thermal insulation

Herein, a novel flexible SiO2 aerogel composite nanofiber membrane with strawberry-like structure and excellent thermal insulation properties, in which SiO2 aerogel particles act as thermal insulation filler, was prepared by electrospinning technology. With the addition of nano-pore structure SiO2 aerogel particles, the heat transfer path of the fibers inside the membrane became discontinuous, endowing the as-prepared membrane an ultra-low thermal conductivity of 30.3 mW/(m⋅K) and large surface area of 240 m2/g. Moreover, the nanofibers membrane also possesses the combined merits of excellent fire resistance, high-temperature stability, and temperature-invariant flexibility, rendering it a promising in the application of insulation and gas adsorption. The successful preparation of this flexible nanofiber membrane paves a new way to design materials with excellent thermal insulation and adsorption properties.

Functionalizing aerogels with tetraazamacrocyclic copper(II) complexes: Nanoenzymes with superoxide dismutase activity

The copper(II) complexes of 1,4,7,10-tetraazacyclododecane (cyclen) and 1,4,8,11- tetraazacyclotetradecane (cyclam) were covalently immobilized in mesoporous silica aerogels by the sol–gel method using functionalized silica precursors. The modified macrocyclic precursors are characterized by mass spectrometry (MS) and solution phase nuclear magnetic resonance (NMR) spectroscopy. The supercritically dried aerogels are characterized using low voltage scanning electron microscopy (LV-SEM), N2-sorption porosimetry, infrared spectroscopy (FT-IR), electron paramagnetic resonance spectroscopy (EPR) and contrast variation small angle neutron scattering (SANS). The suspended aerogel particles act as nanoenzymes, because they have significant SOD activities, dramatically higher than the corresponding dissolved Cu(II) complexes. The most important factors responsible for the altered reactivities due to the covalent immobilization of the complexes were elucidated based on the compiled results of the characterization methods. These are: i) the formation of new chemical environments and Cu(II) coordination modes; ii) the effective separation of the active Cu(II) centers in the aerogels; and iii) the confinement effect operative in the nanoporous network. As a perspective, the present functionalized aerogel microparticles can be developed into passive targeting antioxidant pharmaceutical agents administered locally or subcutaneously.

Effect of particle size on sound absorption behavior of granular aerogel agglomerates

We investigate the sound absorption characteristics of granular aerogel agglomerates of various particle sizes. The normal incidence sound absorption coefficients of six commercially available silica aerogels with different particle size distributions are measured using a two-microphone normal incidence impedance tube. The measurements show a strong correlation between the particle size and sound absorption behavior and reveal important differences between the sound absorption trends of granular aerogel particles larger than 100 μm and those smaller than 50 μm. These differences are further investigated using an inverse characterization method to extract the representative bulk properties necessary to model such agglomerates using the Johnson-Champoux-Allard formulation. Our results show that while agglomerates of larger aerogel granules can be modeled as limp porous media, smaller aerogel granules require a poro-elastic formulation. Further, we show that the inclusion of a logarithmically decreasing dynamic loss factor improves the low-frequency sound absorption predictions of the sub-50 μm aerogels.

Impact ionization dust detection with compact, hollow and fluffy dust analogs

Impact ionization of high-velocity cosmic dust particles has been used as a basic principle for dust detectors in space for many decades. It has provided optimum means to gain insight into the dust environment in the solar system. The Ulysses Dust Detector System provided for the first time impact ionization-based detection of interstellar dust (ISD) in the solar system and discovered surprisingly heavy ISD particles with sizes up to a few microns. Studies based on astronomical observations of the local interstellar medium, on the other hand, suggested a much smaller upper limit of around 0.25 ​μm (silica) or 1 ​μm (graphite) for the size distribution of ISD particles. Therefore, it has been suggested that low-density fluffy dust particles may mimic the impact signals of heavier compact particles. In this work, we discuss a series of impact experiments that have been performed at the Heidelberg dust accelerator facility with the Cosmic Dust Analyzer flight spare unit, to compare the high-velocity impact ionization properties of compact and hollow silicate particles, and carbon aerogel particles with each other and with literature data. The experiments indicate differences in the collected total amount of impact charges and how quickly the charges are collected, between impacts from compact particles and their non-compact counterparts. The results of this first study suggest that fluffy particles generate less ions upon impact than their compact counterparts, opposite to the suggested explanation for the heavy ISD particles. Data from the performed impact experiments indicate that a secondary process (e.g. secondary impacts from ejecta or more target material ionization) could be the main cause for the observed differences. These results imply that the previously detected heavy ISD particles may be real. We identify the key problems with the performed dust experiments and advise that future impact ionization instruments should additionally be calibrated with improved low-density fluffy dust particles that better represent the properties of cosmic dust particles. • Shows new results for impact ionization experiments with non-compact dust particles. • Secondary ionization processes may depend on particle structure and density. • Impact ejecta and target ionization are candidates for relevant secondary processes. • Large and porous in situ interstellar dust particles might likely be real.

Tunable sound packages consisting of granular aerogels and fibrous media

In this study, two granular aerogel materials, both consisting of particles with sizes on the scale of 1 to 50 mm, were first investigated both theoretically and experimentally to improve our understanding of their acoustical behavior. Specifically, layers of the aerogels were evaluated in terms of their sound absorption coefficients, and loss mechanisms in the frequency region below 2000 Hz were quantified for both aerogels by using a previously-developed modeling tool based on the Biot theory. Further studies were then conducted in order to optimize the acoustical performance of potential sound packages featuring these aerogel particle stacks. For example, one of the aerogel materials was placed in series with a fibrous layer to take advantage of the low and high frequency sound absorption offered by the aerogel and the fibrous layers, respectively. The two types of aerogels were also combined in parallel to show that absorption peaks of one of the materials could be used to compensate for the absorption “dips” of the other material. After experimentally validating the design concepts mentioned above, the aerogel granule stacks' properties were tuned to realize a very low frequency and wideband sound absorption treatment when combined with the fibrous layer.

Active Pharmaceutical Ingredients Transportation and Release from Aerogel Particles Processes Modeling

In this work, active pharmaceutical ingredients release from aerogel particles and active pharmaceutical ingredients transportation processes were investigated. Experimental studies were carried out on the release of various types of active pharmaceutical ingredients from various types of aerogel particles. Release curves were obtained. A hybrid model using the lattice Boltzmann method and a cellular automata approach to simulate the release of active pharmaceutical ingredients from aerogel particles and active pharmaceutical ingredients transport processes is proposed. The proposed model can be used in new drug development, which allows partially replacing full-scale experiments with computational ones, therefore reducing the experimental studies cost.

Role of supercritical CO2 impregnation variables on β-carotene loading into corn starch aerogel particles

β-carotene is a natural dye with antioxidant and provitamin A activities, which has essential roles in human health. However, its direct use in food products is unviable since it is susceptible to oxidation, easily isomerization under light, heat or acids, and has low water solubility and oral bioavailability. To address this issue, this work reports, for the first time, the impregnation of β-carotene into corn starch aerogels using supercritical carbon dioxide (sc-CO2). The aerogel particles were produced by the emulsion-gelation method, dried by sc-CO2 and loaded with β-carotene by sc-CO2 impregnation. The impacts of pressure (15 and 30 MPa), temperature (40 and 60 °C), average depressurization rate (0.25–2.61 MPa/min), and cycles (1−4) were investigated on loading. Excepting depressurization rate, all variables played fundamental roles in loading, reaching a maximum of 0.96 mg β-carotene/g aerogel (30 MPa, 40 °C, 0.40 MPa/min, four cycles).

Preparation of robust and self-healing superamphiphobic cotton fabrics based on modified silica aerogel particles

Robust superamphiphobic cotton fabrics with antifouling and self-healing performance were prepared via a simple spraying method. With the composite coating of 1 H, 1 H, 2 H, 2 H- perfluorodecyltriethoxysilane (FAS), FAS modified silica aerogel (F-SiO2), and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), the obtained cotton fabrics showed excellent superamphiphobic properties with a water contact angle (WCA) greater than 170°, and oil contact angle (OCA) of about 158°. The chemical composition, surface morphology and thermal degradation behavior of the products were evaluated. The treated superamphiphobic cotton fabrics displayed excellent robustness against 1600 rubbing cycles, laundering durability and satisfactory chemical stability. Furthermore, the fabricated superamphiphobic coating also exhibited self-healing ability against plasma etching. The work confirmed that cotton fabrics can obtain superamphiphobic property by adjusting the concentration of the F-SiO2 and PVDF-HFP. The facile approach in favor of large-scale preparation showed promising potential for the wide application of flexible superamphiphobic cotton textiles with excellent durability and self-healing performance.

The effects of silica aerogel on the rheological behaviour and polymer matrix structure of Rigid Polyurethane foams

The incorporation of silica aerogel particles into the isocyanate used to prepare Rigid Polyurethane composite foams drastically modifies its rheological behaviour. The isocyanate changes from being a Newtonian fluid of constant viscosity (0.3 Pa s at 25 °C) to a non-linear power-law material with complex viscosity decreasing from 104 to 101 Pa s with a slope −1 versus frequency. The change in response is caused by the formation of a percolated network of particles at contents above 2.5 wt% of aerogel. Moreover, the addition of aerogel significantly slows down the modulus-build up kinetics and vitrification of the matrix by approximately 4.5 min with every 1 wt% of aerogel added. For the foam with 3.0 wt% of aerogel, the combination of high viscosity at early reaction times coupled with the slow modulus build-up impedes the drainage which leads to a decrease in the fraction of material in the struts of the matrix.

Preparation of Vancomycin-Loaded Aerogels Implementing Inkjet Printing and Superhydrophobic Surfaces.

Chronic wounds are physical traumas that significantly impair the quality of life of over 40 million patients worldwide. Aerogels are nanostructured dry porous materials that can act as carriers for the local delivery of bioactive compounds at the wound site. However, aerogels are usually obtained with low drug loading yields and poor particle size reproducibility and urges the implementation of novel and high-performance processing strategies. In this work, alginate aerogel particles loaded with vancomycin, an antibiotic used for the treatment of Staphylococcus aureus infections, were obtained through aerogel technology combined with gel inkjet printing and water-repellent surfaces. Alginate aerogel particles showed high porosity, large surface area, a well-defined spherical shape and a reproducible size (609 ± 37 μm). Aerogel formulation with vancomycin loadings of up to 33.01 ± 0.47 μg drug/mg of particle were obtained with sustained-release profiles from alginate aerogels for more than 7 days (PBS pH 7.4 medium). Overall, this novel green aerogel processing strategy allowed us to obtain nanostructured drug delivery systems with improved drug loading yields that can enhance the current antibacterial treatments for chronic wounds.

Effect of silica aerogel on thermal insulation and acoustic absorption of geopolymer foam composites: The role of aerogel particle size

Silica aerogel features super thermal insulating and excellent sound absorption. Although the application of silica aerogel in building materials for energy saving has been investigated recently, the role of aerogel particle size on geopolymer foam render can be crucial but is rarely studied. In this research, four kinds of silica aerogel with different particle sizes (2–40 μm, 100–700 μm, 100–1200 μm, 700–4000 μm) are applied in geopolymer foam aerogel render (GFAR) to improve the thermal insulation and acoustic absorption performance. Results show that larger silica aerogel particles are more beneficial for acoustic absorption and thermal insulation while smaller aerogel particles are less effective for insulation properties. The microstructure of GFAR is investigated in-depth with micro-CT, optical microscopy and ultrasonic pulse velocity test. The mechanism of the improved performance of GFAR with different silica aerogel is explained. The optimal geopolymer foam aerogel render (GFAR) reaches a thermal conductivity of 0.133 W/(m·K), an average value of acoustic absorption coefficient of 0.51 with a density of 715.2 kg/m3. The result of this study is essential to enlighten the use of larger silica aerogel particles in geopolymer foam render, focusing on a low dosage of silica aerogel while utilize its full benefit.

The dynamic thermal properties of aerogel-incorporated concretes

This study characterizes the dynamic thermal properties of aerogel-incorporated cement composites and other lightweight concretes. The tested specimens were prepared based on three types of aggregates: expanded clay, sintered fly ash aggregate and natural stone aggregate as a reference. The primary method of increasing the overall composite porosity was to prepare specimens by adding aerogel particles. A second method of increasing the cement matrix porosity was obtained using an air-entraining agent. The microstructure of the tested concretes was examined by mercury porosimetry. The novelty of the manuscript is that it presents the comparison of dynamic properties of concretes with the addition of aerogel and other types of lightweight concretes. Thermal properties tests were performed utilizing a non-stationary method. Based on experimentally obtained thermal properties, the values of dynamic thermal characteristics of the tested composites were calculated. The essential part of the experimental research were the tests carried out in non-stationary heat flow conditions in the analyzed composites. The aim of this research was to assess the influence of the thermal properties of a given composite on its behavior in changing temperature conditions. Having the data of the temperature change in specimens and the thermal properties of the tested composites, the total temperature increase, change of the accumulated thermal energy, heat flux, and densities were determined. Based on the experimental data, relationships between physical properties and dynamic thermal characteristics were evaluated.