Organic Inorganic Hybrid Aerogels Research Articles

Facile Fabrication of Hydrophobic and Elastic Silica Aerogels with Enhanced Anti/De-Icing Performance

The anti/de-icing methods are mainly divided into two types: active method and passive method. The passive method generally adopts three ideas: reducing water contact, inhibiting water icing and reducing ice adhesion. Silica aerogels, which have adjustable surface wettability, thermal conductivity and porosity, would be designed to satisfy the requirement for passive anti/de-icing methods. In this work, the organic–inorganic hybrid aerogels based on organosilicon were facilely prepared in a sol–gel procedure, which showed hydrophobic and elastic properties. It could be seen that the thermal insulation effect originating from aerogel-like porous network endowed the efficient anti-icing property. Moreover, the lowest ice adhesion strengths of the above silica aerogels and the related oil-based lubricant-filled aerogels were 7.1[Formula: see text]kPa and 5[Formula: see text]kPa, respectively, which belonged to the icephobic surface. Besides, the ice adhesion strength only increased to 15.6[Formula: see text]kPa after 30 icing–deicing cycles, showing that hydrophobic and elastic silica aerogels had efficient deicing durability.

Multi-scale simulation of stress transfer across ‘polymer bridge’ in graphene oxide/halloysite organic-inorganic hybrid aerogel

In our previous work, organic-inorganic hybrid aerogels were successfully constructed utilizing graphene oxide (GO) sheets and halloysite nanotubes (HNTs), and interesting stress transfer behavior were found. Through preliminary experimental studies, we found that the movement of polymer molecules significantly affected the stress transfer behavior of aerogels. The mechanism might involve macroscopic and microscopic scales, which were difficult to be adequately studied by conventional experimental means. Therefore, this paper investigated the stress transfer behavior of hybrid aerogels utilizing finite element analysis (FEA) combined with molecular dynamics (MD) multi-scale simulation methods. The influence of the connection angles of GO and HNTs on the stress transfer ability was studied utilizing the FEA combined with theoretical formulas. The GO polymer pull-out systems were established by MD. The pull-out processes of polymethylmethacrylate (PMMA) and polysiloxane (PSO) were compared. The effect of oxygen-containing functional group coverage of GO on interface strength was studied. The results indicated that connection angles of 60° and 30° contributed more to the stress transfer between GO and HNTs under tensile and compression stress, respectively. The interfacial enhancement effect of the GO/polymer systems reached saturation when the coverage of oxygen-containing functional groups on the GO surface was 20 %. Si–O–Si agglomeration networks were formed by silane-modified GO and PSO, which possessed stronger interfacial strength.

Superelastic and thermal insulating multilayer organic-inorganic hybrid aerogel built from boron nitride nanoribbons and aramid nanofibers

Thermally insulating aramid nanofiber (ANF) aerogels enable a wide range of applications but are limited by their low mechanical elasticity. Efficient design of aerogels’ components and microstructures is crucial yet remains highly challenging for effectively improving the flexibility of ANF aerogels. Here, for the first time, we report the incorporation of boron nitride nanoribbons (BNNRs) into ANF aerogel to form a multilayer BNNR/ANF hybrid aerogel, which is prepared by suspension mixing of BNNRs and ANFs followed by a vacuum-assisted and directional solidification process. Flexible BNNRs with a high aspect ratio are uniformly embedded in the ANF networks, giving the ANF aerogel an extremely high mechanical deformability (up to 60 % compressive strain), capable of retaining its elasticity even after 100 compression cycles or in liquid N2 (−196 °C). Moreover, the introduction of BNNRs does not reduce the thermal insulation capacity of ANF aerogels, while significantly improving their thermal stability and fire resistance. These excellent multifunctionality benefits from the synergistic effect of organic–inorganic components and the multilayer structure of aerogel. This work paves the avenue for developing next-generation elastic and thermal insulating materials with great potential for widespread applications.

In vitro and in vivo Repair Effects of the NCF-Col-NHA Aerogel Scaffold Loaded With SOST Monoclonal Antibody and SDF-1 in Steroid-Induced Osteonecrosis.

In the current study, we synthesized nanocellulose (NCF)-collagen (Col)-nano hydroxyapatite (NHA) organic-inorganic hybrid aerogels loaded with stromal cell derived factor-1 (SDF-1) and sclerostin monoclonal antibody (SOST McAb) and investigated their ability to repair steroid-induced osteonecrosis. Rabbit bone marrow mesenchymal stem cells (BMSCs) and human vascular endothelial cells (HUVECs) were used for the in vitro study. A rabbit steroid-induced osteonecrosis model was used for the in vivo study. The best elastic modulus reached 12.95 ± 4.77 MPa with a mean compressive property of 0.4067 ± 0.084 MPa for the scaffold containing 100% mass fraction. The average pore diameter of the aerogel was 75 ± 18 µm with a porosity of more than 90% (96.4 ± 1.6%). The aerogel-loaded SDF-1 and SOST were released at 40–50% from the material within the initial 3 h and maintained a stable release for more than 21 days. The in vitro study showed osteogenesis and vascularization capabilities of the scaffold. The in vivo study showed that rabbits received implantation of the scaffold with SOST McAb and SDF-1 showed the best osteogenesis of the osteonecrosis zone in the femoral head. Imaging examination revealed that most of the necrotic area of the femoral head was repaired. These results suggest that this hybrid aerogel scaffold could be used for future steroid-induced osteonecrosis repair.

Versatile Route for Multifunctional Aerogels Including Flaxseed Mucilage and Nanocrystals.

Preparation of low density monolithic and free-standing organic-inorganic hybrid aerogels of various properties is demonstrated using green chemistry from a biosafe natural source (flaxseed mucilage) and freeze-casting and subsequent freeze drying. Bio-aerogels, luminescent aerogels, and magneto-responsive aerogels are obtained by combination of the flaxseed mucilage with different types of nanoparticles. Moreover, the aerogels are investigated as possible drug release systems using curcumin as a model. Various characterization techniques like thermogravimetric analysis, nitrogen physisorption, electron microscopy, UV/Vis absorption, and emission spectroscopy, bulk density, and mechanical measurements, as well as in vitro release profile measurements, are employed to investigate the obtained materials. The flaxseed-inspired organic-inorganic hybrid aerogels exhibit ultra-low densities as low as 5.6mg cm-3 for 0.5% (w/v) the mucilage polymer, a specific surface area of 4 to 20 m2 g-1 , high oil absorption capacity (23g g-1 ), and prominent compressibility. The natural biopolymer technique leads to low cost and biocompatible functional lightweight materials with tunable properties (physicochemical and mechanical) and significant potential for applications as supporting or stimuli responsive materials, carriers, reactors, microwave- and electromagnetic radiation protective (absorbing)-materials, as well as in drug delivery and oil absorption.

Off/on switchable smart electromagnetic interference shielding aerogel

Summary Smart electromagnetic interference (EMI) shielding materials with tunable EM wave response characteristics are attractive for future EM devices. Here, we report an off/on switchable EMI shielding material that can be tuned from EM wave transmission to shielding and vice versa by mechanical compression and decompression. This smart material is prepared by filling conductive carbon nanoparticles into wood-derived lamellar carbon aerogel, showing reversible compressibility and strain-sensitive conductivity. The original aerogel has good impedance matching and low dielectric loss, allowing the EM wave to pass through. Mechanical compression enables the carbon nanoparticles to establish highly conductive pathways in the aerogel, which significantly increases the conductivity of aerogel and thus activates its EMI shielding performance. This function switch is reversible by repeatedly compressing and decompressing the aerogel. The availability of such a never-before-realized off/on switchable EMI shielding material provides an opportunity for the development of advanced smart EM devices.

A novel multi-dimension inorganic–organic hybrid aerogel and its electrochemical behavior

Halloysite nanotubes (HNTs) were widely concerned in the research of electrode materials for supercapacitors because it had many advantages, such as abundant natural reserves, non-toxic, large specific surface area, and so on. The zero-dimensional Fe3O4 nanoparticles loaded onto the surface of one-dimensional HNTs (HNTs-O) could give HNT’s excellent electrical properties and improve the specific capacitance. In our previous study, the HNTs were connected into three-dimensional interconnected nano-network (HCAs) by electrostatic interaction. It was found interesting phenomena in load transfer ability and increasing the specific surface area. Based on our previous studies, in this study, HNTs-O was compounded with the three-dimensional HCAs to prepare the composite aerogel (CA-O). The organic–inorganic hybrid aerogels (CA-OP) were prepared by loading conductive polymer polyaniline (PANI) onto the composite aerogel surface to form a two-dimensional PANI. The synergistic effect of inorganic HNTs-O and organic PANI had improved the conductivity and electrical properties of CA-OP. The results of the scanning electron microscope, Fourier transform infrared, N2 adsorption–desorption, stress–strain tests, and so on showed that the composite was successfully prepared and had the acceptable performance in specific surface area and mechanical properties. Cyclic voltammetry, electrochemical impedance spectroscopy, and other electrochemical tests suggested that the organic–inorganic hybrid aerogel had large capacitance and exciting cycle performance.

Polyimide Aerogel Fibers with Superior Flame Resistance, Strength, Hydrophobicity, and Flexibility Made via a Universal Sol-Gel Confined Transition Strategy.

Aerogel fibers with ultrahigh porosity, large specific surface area, and ultralow density have shown increasing interest due to being considered as the next generation thermal insulation fibers. However, it is still a great challenge to fabricate arbitrary aerogel fibers via the traditional wet-spinning approach due to the obvious conflict between the static sol-gel transition of the aerogel bulks and the dynamic wet-spinning process of aerogel fibers. Herein, a sol-gel confined transition (SGCT) strategy was developed for fabricating various mesoporous aerogel fibers, in which the aerogel precursor solution was first driven by the surface tension into the capillary tubes, then the gel fibers were easily formed in the confined space after static sol-gel process, and finally the mesoporous aerogel fibers were obtained via the supercritical CO2 drying process. As a typical case, the polyimide (PI) aerogel fiber prepared via the SGCT approach has exhibited a large specific surface area (up to 364 m2/g), outstanding mechanical property (with elastic modulus of 123 MPa), superior hydrophobicity (with contact angle of 153°), and excellent flexibility (with curvature radius of 200 μm). Therefore, the aerogel woven fabric made from PI aerogel fibers has possessed an excellent thermal insulation performance in a wide temperature window, even under the harsh environment. Besides, arbitrary kinds of aerogel fibers, including organic aerogel fibers, inorganic aerogel fibers, and organic-inorganic hybrid aerogel fibers, have been fabricated successfully, suggesting the universality of the SGCT strategy, which not only provides a way for developing aerogel fibers with different components but also plays an irreplaceable role in promoting the upgrading of the fiber fields.

Loads transfer behavior of graphene oxide/halloysite organic-inorganic hybrid aerogel: Motion of polymer ‘bridge’

Loads transfer behavior of graphene oxide/halloysite organic-inorganic hybrid aerogel: Motion of polymer ‘bridge’

A novel graphene oxide/halloysite hybrid aerogel linked by glassy polymer

In our previous research, origami graphene aerogel and halloysite aerogel were successfully prepared, and interesting results were also found in terms of structural self-reinforcement and stress to transfer behavior. As an aerogel, it is always the result of mechanical strength. Based on the previous research, we proposed the idea of ​preparing organic-inorganic hybrid aerogels using graphene oxide and halloysite. By using the glassy polymer Polymethylmethacrylate (PMMA) as a medium, graphene oxide (GO) and halloysite (HNTs) are connected to the aerogel structure. The microstructure and mechanical properties of the hybrid aerogel were studied. The results showed that a semi-organic semi-inorganic halloysite-graphene aerogel (HGA) with a three-dimensional network structures were successfully prepared. Its pore structure was mainly mesopores, and its thermal stability was improved. HGA had good mechanical properties, even if the number of cycles was as high as 50 times, the mechanical strength was still at a relatively high level. HGA contains organic and inorganic networks, and load to transfer is easier than graphene aerogel transfer.

Atomic Layer Deposition onto Thermoplastic Polymeric Nanofibrous Aerogel Templates for Tailored Surface Properties.

Poly(vinyl alcohol-co-ethylene) (EVOH) nanofibrous aerogel (NFA) templates were fabricated through vacuum freeze-drying from EVOH nanofibrous suspensions. Aluminum oxide (Al2O3) layers were deposited onto highly porous templates to form organic-inorganic hybrid aerogels by the atomic layer deposition (ALD) technique. Chemical and physical measurements showed that mechanical properties were improved through ALD. In addition, the surface chemistry of ALD modified aerogels showed a fascinating cyclic change based on the number of ALD deposition cycles. A transition from hydrophilicity to hydrophobicity was observed after a few cycles of ALD coating; however, additional deposition cycles changed the wettability characteristics back to hydrophilicity. This hydrophilic-hydrophobic-hydrophilic variation is shown to be governed by a combination of geometrical and chemical surface properties. Furthermore, the deposited Al2O3 could substantially improve aerogels strength and reduce permanent deformation after cyclic compression. The Young's modulus of aerogels increased from 5.54 to 33.27 kPa, and the maximum stress at 80% strain went up from 31.13 to 176.11 kPa, after 100 cycles of trimethyl-aluminum (TMA)/water ALD. Thermogravimetric analysis (TGA) results confirm that ALD can effectively improve the heat resistance characteristics of polymeric aerogel. The onset temperature and the residual mass increased with increasing numbers of ALD cycles. During pyrolysis, the nanofiber cores were decomposed, and the brittle pure Al2O3 self-supporting nanotube aerogels with the continuous hollow nanotubular network were formed. A coating of continuous thickness Al2O3 layer on individual nanofiber was achieved after 100 ALD cycles. In additional to mechanical strength and physical property changes, the ALD modified aerogel also shows a superhydrophobic and oleophilic surface chemistry, which could potentially be used to remove oils/organic solvents from water. The resultant aerogels exhibit excellent absorption capacity (31-73 g/g) for various liquids, and the material could be reused after distillation or squeezing. A successful scale-up of such materials could provide some insights into the design and development of thermoplastic polymeric NFAs with substantial industrial applications.

Preparation and loads transfer behaviour of graphene/halloysite organic–inorganic hybrid aerogel

Aerogel materials have wide research and application in the fields of thermal insulation and functional materials. Although graphene sheet has high strength in conventional graphene aerogels, the interaction between sheets is weak. The overall strength of graphene aerogels is not high enough. Aerogels, especially halloysite aerogels, have been successfully synthesised in recent years, but their electrical potential expansion is slightly insufficient. Therefore, in view of the enhancement of the mechanical properties of aerogels and the development of electrical potential, the idea of organic–inorganic hybrid (OIH) aerogel was proposed. Graphene halloysite OIH aerogel materials were prepared by graphene sheets and halloysite fibres. The preparation and microstructure of materials were characterised using Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and nitrogen adsorption–desorption. Meanwhile, the mechanical properties of aerogels were also studied, and the stress transfer behaviour of aerogels was investigated by Raman spectroscopy. The results showed that the OIH aerogel was successfully obtained. The strength of the OIH aerogels was much higher than that of the mixture of graphene and halloysite aerogel. The OIH network aerogels had more effective stress transfer effect depending on the chemical bonds between the networks.

Structural and mechanical properties of hybrid silica aerogel formed using triethoxy(1-phenylethenyl)silane

Abstract Aerogels are highly porous materials with potential application in thermal super-insulators for smart energy devices. Until now, the commercialization of silica-based aerogels has been restricted due to their brittle nature, and this drawback needs to be overcome by the improvement in the mechanical properties. Therefore, for the first time, the silane-based precursor triethoxy(1-phenylethenyl)silane (TPS) was introduced to synthesize the hybrid organic-inorganic aerogels. The simple, fast, and cost-effective free radical polymerization method was adopted to prepare TPS precursor. In present work, the tetraethylorthosilicate and TPS were introduced together at different molar ratios followed by hydrolysis-condensation and supercritical CO2 drying to achieve hybrid aerogels. The remarkable increase in the mechanical strength and hydrophobicity was found in the phenyl/vinyl hybridized aerogels compared with pristine silica aerogels. This facile synthesis approach provides new method to decorate the organic-inorganic hybrid aerogels.

Microwave Absorbing Materials: Multifunctional Organic–Inorganic Hybrid Aerogel for Self‐Cleaning, Heat‐Insulating, and Highly Efficient Microwave Absorbing Material (Adv. Funct. Mater. 10/2019)

Microwave Absorbing Materials: Multifunctional Organic–Inorganic Hybrid Aerogel for Self‐Cleaning, Heat‐Insulating, and Highly Efficient Microwave Absorbing Material (Adv. Funct. Mater. 10/2019)

Multifunctional Organic–Inorganic Hybrid Aerogel for Self‐Cleaning, Heat‐Insulating, and Highly Efficient Microwave Absorbing Material

AbstractMultifunctionalization is the future development direction for microwave absorbing materials, but has not yet been explored. The effective integration of multiple functions into one material remains a huge challenge. Herein, an aerogel‐type microwave absorber assembled with multidimensional organic and inorganic components is synthesized. Polyacrylonitrile fibers and polybenzoxazine membranes work as the skeleton and crosslinker, respectively, forming a 3D framework, in which carbon nanotubes are interconnected into an electrically conductive network, and Fe3O4 nanoparticles are uniformly dispersed throughout the aerogel. Remarkably, the microwave absorption performances of the aerogel achieve ultralight, ultrathin (1.5 mm), and strong absorption (reflection loss of −59.85 dB) features. In particular, its specific reflection loss values considerably outperform the current magnetic–dielectric hybrids with similar components. Moreover, the aerogel possesses strong hydrophobicity and good thermal insulation, endowing it attractive functions of self‐cleaning, infrared stealth, and heat insulation that is even comparable to commercial products. The excellent multifunction benefits from the cellular structure of aerogel, the assembly of multidimensional nanomaterials, and the synergistic effect of organic–inorganic components. This study paves the way for designing next‐generation microwave absorbing materials with great potential for multifunctional applications.

Hybrid silicone aerogels toward unusual flexibility, functionality, and extended applications

Here, we overview the developments in the past decade made on organic–inorganic hybrid aerogels and xerogels based on silicone (polyorganosiloxanes) through persistent works by the authors to increase the mechanical strength and flexibility and add functionality. Polymethylsilsesquioxane (PMSQ, CH3SiO3/2) has been found to show unusual strength and flexibility against compression, and their bending properties can also be improved by several strategies. Silicone-based networks with organic bridges between inorganic moieties are also beneficial for these improvements. In particular, organic bridges with a higher fraction and more extended length have been found to allow higher durability against large deformations. In addition, functional groups such as vinyl, chloromethyl, and amino can readily be introduced by starting from organoalkoxysilanes with these functional substituents (e.g., FG−Si(OR)3 or (RO)3Si−FG−Si(OR)3, where FG shows an organic substituent containing functional groups and R is typically methyl or ethyl), and other functional groups such as carboxyl can be introduced by post-gelation modifications on the pre-installed FG in the network. Possibilities in applications such as thermal insulators, photoluminescent media, and photocatalysts are also discussed.

Origin of Flexibility of Organic–Inorganic Aerogels: Insights from Atomistic Simulations

Silica aerogel has a variety of excellent properties, but the mechanical brittleness inhibits the practical applications. Recently, many experimental efforts have been made to improve the compressibility and bendability of aerogels by hybridization with organic materials; however, the reason of the flexibility has not yet been well understood. To identify the intrinsic origins of the flexibility of organic–inorganic hybrid aerogels, polymerization and mechanical responses of tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMS), and 1,2-bis(methyldiethoxysilyl)ethane (BMDEE) polymers were investigated by using reactive molecular dynamics simulations. As a result, cyclic compressive deformation simulations successfully reproduce the experimental results that TMOS is substantially fragile, whereas MTMS and BMDEE are easy to be reshaped. Detailed structure analyses showed that Si–O–Si–O rings in TMOS are collapsed by compressive deformation, whereas any kind of ring structure in BMDEE is maintained even after large compression. Tetrahedral SiO4-based network structure (Q4) in TMOS is found to be the source of the brittleness. On the contrary, the absence of Q4 silicones and the presence of ethylene units, which provide rotatable dihedrals, in BMDEE allow it to deform without disrupting the microscale network. The insightful information provided by the theoretical investigation in atomistic scale is essential to design new composite aerogels.

Superflexible Multifunctional Polyvinylpolydimethylsiloxane-Based Aerogels as Efficient Absorbents, Thermal Superinsulators, and Strain Sensors.

Aerogels are porous materials but show poor mechanical properties and limited functionality, which significantly restrict their practical applications. Preparation of highly bendable and processable aerogels with multifunctionality remains a challenge. Herein we report unprecedented superflexible aerogels based on polyvinylpolydimethylsiloxane (PVPDMS) networks, PVPDMS/polyvinylpolymethylsiloxane (PVPMS) copolymer networks, and PVPDMS/PVPMS/graphene nanocomposites by a facile radical polymerization/hydrolytic polycondensation strategy and ambient pressure drying or freeze drying. The aerogels have a doubly cross-linked organic-inorganic network structure consisting of flexible polydimethylsiloxanes and hydrocarbon chains with tunable cross-linking density, tunable pore size and bulk density. They have a high hydrophobicity and superflexibility and combine selective absorption, efficient separation of oil and water, thermal superinsulation, and strain sensing.

Versatile Double-Cross-Linking Approach to Transparent, Machinable, Supercompressible, Highly Bendable Aerogel Thermal Superinsulators

A facile yet versatile approach to transparent, highly flexible, machinable, superinsulating organic–inorganic hybrid aerogels is presented. This method involves radical polymerization of a single alkenylalkoxysilane to obtain polyalkenylalkoxysilane, and subsequent hydrolytic polycondensation to afford a homogeneous, doubly cross-linked nanostructure consisting of polysiloxanes and hydrocarbon polymer units. Here we demonstrate that novel aerogels based on polyvinylpolysilsesquioxane (PVPSQ), polyallylpolysilsesquioxane (PAPSQ), polyvinylpolymethylsiloxane (PVPMS), and polyallylpolymethylsiloxane (PAPMS) are facilely prepared via this approach from vinyltrimethoxysilane (VTMS; or vinyltriethoxysilane, VTES), allyltrimethoxysilane (ATMS; or allyltriethoxysilane, ATES), vinylmethyldimethoxysilane (VMDMS), and allylmethyldimethoxysilane (AMDMS), respectively. These aerogels combine low density, uniform nanopores, high transparency, supercompressibility, high bendability, excellent machinability, and thermal...

Amyloid Templated Organic–Inorganic Hybrid Aerogels

AbstractThis feature article covers the recent developments of amyloid fibrils as templates for organic–inorganic hybrid aerogels. It aims at introducing the reader to amyloid fibril functional bio‐nanomaterials and to show how, building on the prior art of colloidal aerogels, these anisotropic colloids can be used to template inorganic particles and to form gels and aerogels. Specifically, hybrid organic–inorganic amyloid fibril templated gold, silver, and calcium aerogels are discussed focusing on their material synthesis and how the preparation conditions can be tuned to vary the final materials' optical, structural, and mechanical properties. The colloidal processing methodology offers a convenient route to form gels and aerogels that maintain the nanoscopic dispersion properties within the formed monoliths. These ultralight porous materials are appealing for a diverse set of applications within food, fine arts, jewelry, and biomedicine. Here their use as pressure sensor, catalysis membrane, and antibacterial material are described and further applications based on the properties of the specific inorganic particles and hybrid aerogels are discussed.