Superhydrophobic Silica Aerogels Research Articles

Superdurable Full-Life Superhydrophobic Composite Block.

Superhydrophobic materials are attractive for industrial development but plagued by poor mechanical stability. Herein, a superdurable full-life superhydrophobic composite block is designed and fabricated by embedding near-zero contractive superhydrophobic silica aerogel into a rigid iron-nickel foam structured similarly to a regular dodecahedron. The synergistic protection afforded by these materials ensures superrobust mechanical stability for the composite block, which features a high compressive strength of up to ≈7.4MPa, and ultralow Taber abrasion of down to ≈0.567mm after withstanding 50000 cycles, and highly efficient water harvesting capability of up to ≈3114.3mg min-1 cm-2 at a supercooling degree of 40 K. This robust material system provides a novel strategy to design superhydrophobic materials capable of withstanding extreme conditions, including high temperature, humidity, pressure, and abrasion.

Performance Enhancement of Silicone Rubber Using Superhydrophobic Silica Aerogel with Robust Nanonetwork Structure and Outstanding Interfacial Effect.

The application of high-performance rubber nanocomposites has attracted wide attention, but its development is limited by the imbalance of interface and network effects caused by fillers. Herein, an ultrastrong polymer nanocomposite is successfully designed by introducing a superhydrophobic and mesoporous silica aerogel (HSA) as the filler to poly(methyl vinyl phenyl) siloxane (PVMQ), which increased the PVMQ elongation at break (∼690.1%) by ∼9.3 times and the strength at break (∼6.6 MPa) by ∼24.3 times. Furthermore, HSA/PVMQ with a high dynamic storage modulus (G'0) of ∼12.2 MPa and high Payne effect (ΔG') of ∼9.4 MPa is simultaneously achieved, which is equivalent to 2-3 times that of commercial fumed silica reinforced PVMQ. The superior performance is attributed to the filler-rubber interfacial interaction and the robust filler-rubber entanglement network which is observed by scanning electron microscopy. When the HSA-PVMQ entanglement network is subjected to external stress, both the HSA and bound-PVMQ chains are synergistically involved in resisting structural evolution, resulting in the maximized energy dissipation and deformation resistance through the desorption of the polymer chain and the slip/interpenetrating of the exchange hydrogen bond pairs. Hence, highly aggregated nanoporous silica aerogels may soon be widely used in the application of reinforced silicone rubber or other polymers shortly.

Superhydrophobic and Highly Elastic Strain‐Sensing Fiber Embedded with Carbon Nanotubes and Aerogels Based on the Dipping and Drying Method

AbstractFor a fiber‐based strain sensor to be used as a wearable device, its conductivity and sensing characteristics should be stably maintained even during repeated mechanical movements. Additionally, the sensing characteristics should remain unaffected by external contaminants, such as water or sweat, as the sensor is expected to be in contact with the human body. In this study, a superhydrophobic and highly elastic strain‐sensing fiber with durability against continuous tension and contraction while maintaining a stable sensing performance even when in contact with water and sweat is developed. A carbon nanotube is embedded, which is a highly conductive material, inside a spandex fiber with high elasticity and shape recovery rate, enabling the stable measurement of repetitive joint movements under various strain conditions. Furthermore, a superhydrophobic silica aerogel is embedded inside the spandex fiber to facilitate stable sensing without malfunction even when exposed to external contaminants. The proposed strain‐sensing fiber can monitor joints of the human body during various movements, such as dumbbell pressing, squatting, walking, and running. Therefore, the study findings can contribute to the development of wearable healthcare devices that warrant reliable sensing.

Modulating pore microstructure of silica aerogels dried at ambient pressure by adding N-hexane to the solvent

In this work, a kind of superhydrophobic silica aerogels was prepared at ambient pressure using tetraethoxysilane (TEOS) as precursor. Particularly, N-hexane was added in the solvent to modulation pore microstructure and effect on the insulation properties of samples were analyzed. It is discovered that when the volume ratio of N-hexane to TEOS is 1:2.24 the thermal conductivity of samples can reach the lowest of 0.012 W/m·K. Compared with that of samples no addition of N-hexane, the density is decreased, the theoretical average pore size increases and the total pore volume increases. Due to N-hexane it leads cross-linking between the sol particles stronger and inhomogeneous. Thus gelation process is speeded up resulting in a change in pore structure. Low density can reduce the solid-phase heat transfer, perfect pore microstructure reduces the contribution of gas-phase heat transfer, and only when the two aspects forms a suitable combination it can exhibit optimal thermal insulation performance.

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.

Super-hydrophobic and resilient hybrid silica aerogels for thermal insulation, energy harvesting, and electrical applications in harsh environments

Vinyltrimethoxysilane (VTMS) was successfully grafted onto the polymethylhydrosiloxane (PMHS) chain, resulted in flexible and superhydrophobic silica aerogels with robust structural integrity.

The effect of synthesis parameters on pore diameter of superhydrophobic silica aerogel prepared at ambient pressure

Silica aerogels were prepared by the sol-gel method and dried at ambient pressure with sodium silicate precursor. The prepared aerogel is superhydrophobic. The effect of various synthesis conditions on pore structure and diameter was investigated. The results of N2 adsorption-desorption isotherms, BET theory, BJH method, and field emission scanning electron microscopy images showed that by changing the surface modification method, the porosity of the samples changes. The order of increasing the average pore diameter for different protic solvents is isopropanol < methanol < ethanol. The specific surface area and total pore volume also increase with the increasing concentration of citric acid citric. The sample surface modified with HMDZ has smaller average pore diameters and total pore volume than the sample surface modified with TMCS. With increasing temperature, the average pore diameter and total pore volume increase, and the BET surface decreases.

Insight into ultra-flexible & robust silica aerogels based on diene synthesis reaction: Preparation and oil/water separation

This paper reported the preparation of ultra-flexible silica aerogels based on diene synthesis reaction at atmospheric pressure. Vinyl trimethoxy silane and vinyl methyl dimethoxy silane as silicon source were used to prepare vinyl aerogels by one-pot acid-base sol–gel route. The diene synthesis reaction was used to prepare ultra-flexible and super hydrophobic silica aerogels on the basis of vinyl aerogels. Maximum strain of the ultra-flexible aerogels is as high as 90 % for 20 compression-decompression cycles. The aerogels can be recovered completely without structure destruction. In addition, the adsorption capacity of the samples is higher than that of the conventional silica aerogels, which can reach to 15.0 g⋅g−1 of dichloromethane. It is worth noting that they also have efficient cycle performance for adsorption and filtration. Acting as core part of filtration, the organic solvents insoluble in water can be easily separated from water by the aerogels.

High efficiency fluorescent perovskite quantum dots encapsulated in superhydrophobic silica aerogel for wide color gamut backlight displays

• A super-hydrophobic Silica Aerogels film for backlight display was prepared. • A wide gamut of 128% of color gamut of NTSC standard was achieved. • Excellent environmental stability was achieved through a composite strategy. Recently, all-inorganic cesium lead halide (CsPbX 3 ) perovskite quantum dots (PQDs) have been widely used in the photoelectric field. However, a major limitation of solution-processed PQDs for applications is inherent instability. Herein, we adopt strategy of passivation, CsPbX 3 (X = Cl, Br, I) PQDs are encapsulated into super-hydrophobic silica aerogels (SiO 2 AGs) to form a protective layer for resisting destruction by external forces. Importantly, the photoluminescence quantum yield (PLQY) of CsPbBr 3 @AGs composites achieves 71%, CsPbCl 2 Br 1 @AGs, CsPbBr 3 @AGs and CsPbBr 1 I 2 @AGs composites with narrow emissions can replace traditional phosphors as color converters. In addition, a high-performance liquid crystal display (LCD) with a wide color gamut (128% of National Television System Committee color space) is demonstrated using the prepared CsPbX 3 @AGs@PS composite film and blue light emitting diode (LED) chip as backlight. The combination of improved stability and wide color gamut of the perovskite material provides a viable approach for LCD backlight.

Superhydrophobic Silica Aerogels and Their Layer-by-Layer Structure for Thermal Management in Harsh Cold and Hot Environments.

Personal thermal management (PTM) materials have recently received considerable attention to improve human body thermal comfort with potentially reduced energy consumption. Strategies include passive radiative cooling and warming. However, challenges remain for passive thermal regulation of one material or structure in both harsh hot and cold environments. In this work, silica aerogels derived from sodium silicate were prepared through a solvent-boiling strategy, where hydrophobization, solvent exchange, sodium purification, and ambient pressure drying (HSSA) proceeded successively and spontaneously in a one-pot process. This strategy leads to the synthesis of superhydrophobic silica aerogels with extremely low energy consumption without out the use of an ion-exchange resin or low surface tension solvents. Silica aerogels possess a high specific surface area (635 m2/g), high contact angle (153°), and low thermal conductivity (0.049 W/m K). A layer-by-layer (LBL) structure including the silica aerogel layer and an extra phase change material layer was designed. The structure demonstrates dual-functional thermal regulation performance in both harsh cold (-30 °C) and hot (70 °C) environments, where the time to reach equilibrium is postponed, and the inner temperature of the LBL structure can be kept above 20 °C in harsh cold environments (-30 °C) and below 31 °C in harsh hot environments (70 °C). A proof-of-concept experimental setup to simulate the illumination of sunlight also proved that the inside temperature of a model car protected by the LBL structure was below 28 °C, while the outside temperature was 70 °C. In addition, these results are well supported by theoretical COMSOL simulation results. The findings of this work not only provide an eco-friendly approach to synthesize silica aerogels but also demonstrate that the LBL structure is a robust dual-functional PTM system for thermal regulation in both harsh hot and cold environments.

Solid-Liquid-Vapor Triphase Gel.

Gels are soft functional materials with solid networks and open pores filled with solvents (for wet gels) or air (for aerogels), displaying broad applications in tissue engineering, catalysis, environmental remediation, energy storage, etc. However, currently known gels feature only a single (either solid-liquid or solid-vapor) interface, largely limiting their application territories. Therefore, it is both fundamentally intriguing and practically significant to develop conceptually new gel materials that possess solid-liquid-vapor multiple interfaces. Herein, we demonstrate a unique solid-liquid-vapor triphase gel, named as aerohydrogel, by gelling of a poly(vinyl alcohol) aqueous solution with glutaraldehyde in the presence of superhydrophobic silica aerogel microparticles. Owing to its continuous solid, liquid, and vapor phases, the resultant aerohydrogel simultaneously displays solid-liquid, solid-vapor, and liquid-vapor interfaces, leading to excellent properties including tunable density (down to 0.43 g·cm-3), considerable hydrophobicity, and excellent elasticity (compressive ratio of up to 80%). As a proof-of-concept application, the aerohydrogel exhibits a higher evaporative cooling efficiency than its hydrogel counterpart and a better cooling capability than the commercial phase change cooling film, respectively, showing promising performance in cooling various devices. Moreover, the resulting aerohydrogel could be facilely tailored with specific (e.g., magnetic) properties for emerging applications such as solar steam generation. This work extends biphase gel (hydrogel or aerogel) to solid-liquid-vapor triphase gel, as well as provides a promising strategy for designing more aerohydrogels serving as soft functional materials for applications in various emerging fields.

High-efficiency Ca2+ doping all-inorganic nanocrystals (CsPbBr3 and CsPbBr1I2) encapsulated in a superhydrophobic aerogel inorganic matrix for white light-emitting diodes

All-inorganic halide perovskite nanocrystals (NCs) have become the most promising next generation luminescent materials due to their excellent properties. However, there are many nonradiative recombination defects in colloidal perovskite NCs, which reduce their luminescent efficiency and stability. In this work, we incorporated the alkaline-earth (AE) metal ion Ca2+ into NCs to further improve the photoluminescence quantum yield (PLQY) of CsPbBr3 and CsPbBr1I2 NCs. The PLQY of green-emitting CsPbBr3 and red-emitting CsPbBr1I2 NCs can be boosted to 72.3% and 78.7%, respectively by doping the optimum amount of Ca2+. At the same time, we adopted a simple and low-cost one-pot method to integrate Ca2+-CsPbX3 (X3 = Br3, Br1I2) NCs and superhydrophobic silica aerogels (AG), not only retaining the high PLQY of NCs, but also greatly improving the water, heat and light stability. Finally, the green-emitting Ca2+-CsPbBr3@AG, red-emitting Ca2+-CsPbBr1I2@AG composites and the blue chip as the light sources show a wide color gamut that accounts for 129% of the NTCS 1953 value and nearly 100% of the Rec.2020 value. Additionally, we fabricated white light-emitting diode (WLED) devices by coupling Ca2+-CsPbBr1I2@AG composites with commercial YAG:Ce3+ phosphors on blue chips, obtaining bright white light with a color rendering index (CRI) up to 92.2.

A novel preparation of superhydrophobic silica aerogels via the combustion drying method

Silica aerogels with prominent physical, thermal, optical, and acoustic properties are considered to be highly promising materials. However, owing to the high cost and the complex production processes associated with existing drying technologies, the application of silica aerogels is limited in many fields. In this study, a novel combustion drying method (CDM) was successfully used in the synthesis of superhydrophobic silica aerogels for the first time. It was confirmed that silica aerogel prepared by CDM has a typical aerogel structure with low density, high porosity, high specific surface area, high total pore volume, superhydrophobicity and high thermal stability. Compared with supercritical fluid drying, freeze drying and ambient pressure drying, CDM possesses significant advantages in the drying efficiency and low-cost production due to its active drying mode. Finally, the mechanism of the combustion drying method is proposed based on the combustion of organic solvents. The results will be meaningful for the design and production of aerogel materials in the future.

Performance regulation of silica aerogel powder synthesized by a two-step Sol-gel process with a fast ambient pressure drying route

This paper proposed a timesaving route for preparing silica aerogel powder with TEOS as a precursor. Thermal insulating super hydrophobic silica aerogel powder was synthesized by combining two-step Sol-gel reaction with a fast ambient pressure drying process. Silica Sol-gel was formed after catalytic reaction by oxalic acid and NH4OH, and then turned to be hydrophobic aerogel through further surface modification (only three hours with no solvent exchange process) and drying process. By optimizing every tiny trace of synthetic component, the obtained silica aerogel powder exhibits excellent properties, such as low apparent density (0.212 g/cm3) and thermal conductivity (0.053 W/mK), as well as high BET surface area (769.86 m2/g) and water contact angle (149.0 °). This work presents a timesaving method for synthesizing thermal insulating hydrophobic silica aerogel powder.

Eco-friendly approach for preparation of water-based superhydrophobic silica aerogels via ambient pressure drying

In this work, superhydrophobic methyltrimethoxysilane (MTMS)-based silica aerogels were fabricated via water-based sol–gel reaction by ambient pressure drying (APD) method in the presence of surfactant. The structure, morphology, and hydrophobic properties of the obtained silica aerogel were characterized by scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) methods, X-ray diffractometer (XRD), and water contact angle measurement. The effects of the concentration of MTMS, the pH value of the solution, and the amount of surfactant cetyltrimethylammonium bromide (CTAB) on properties of silica aerogels were investigated, respectively. Increasing the concentration of MTMS to a great extent resulted in higher density and lower porosity of silica aerogel. Alkali catalyst was an extremely crucial factor for preparing silica aerogels. With the increase of the pH value from 7.5 to 10 the gelation time of the prepared aerogels was observed to decrease from 40 min to 2 min, and the shrinkage of aerogel sample decreased from 15.5% to 3.5%. The skeleton structure of the prepared silica aerogel gradually transformed from coarsened spherical to continuous irregularity finer structures with the increased concentration of CTAB. In addition, the prepared silica aerogel showed outstanding anti-adhesion property and superhydrophobic ability with a water contact angle (WCA) of 160.6 ± 1.3°.

Structural, out-gassing and nanomechanical properties of super-hydrophobic transparent silica aerogels developed by ambient pressure drying for space application

Transparent super-hydrophobic monolithic silica aerogels are prepared by the cost-effective ambient pressure drying. The drying of aerogel is performed at various temperatures ranging from 25 to 200°C. Oxidation states of different silica aerogels are investigated by XPS which shows the presence of both SiO and SiO2 phases. Thermal stability of hydrophobic aerogel is found as ~320°C investigated by TGA and DSC. The chemical bonds (i.e., –CH3) responsible for the hydrophobic (WCA > 170°) nature of synthesized silica aerogels are identified by FTIR. Further, out-gassing properties of the silica aerogels have been investigated and they are found in limit for the space application. The highest hardness and Young’s modulus are measured by the nanoindentation technique for the aerogel dried at 120°C which has higher density, while density decreases for the aerogel dried at 200°C and the corresponding nanomechanical properties are found to be lowest as expected.

Synthesis of multi-functional porous superhydrophobic trioxybenzene cross-linked silica aerogels with improved textural properties

The development of organically modified cross-linked silica aerogels with an ordered porous structure and a high surface area is of utmost importance for practical applications. However, practical applications have been limited, as the organic cross-linkers lead to decrease the textural properties due to large phase separation and large size difference between organic and inorganics. Also cross-linkers are not commercially available or are prohibitively expensive. To overcome these, we proposed to use small size organic cross-linker i. e aryl group with three cross-linking sites to minimize phase separation and to obtain ordered silica network. Initially, three cross-linkers are synthesized starting from trihydroxybenzene and tetraethoxysilane using acid catalyst. Further, using these cross-linkers, trioxybenzene cross-linked silica aerogels were prepared by a simple cost-effective sol-gel process. Three different structural isomers of trihydroxybenzene precursors were used to analyze its suitability to obtain cost-effective silica aerogels with high porosity and hydrophobicity. Among these cross-linked silica aerogels, 1,3,5-trihydroxybenzene cross-linked aerogels possess a high surface area (1268 m2/g) and uniform porous morphology with a highly interconnected structure due to symmetry and lower phase separation. It also exhibits low density (0.02431 g/cm3) and low shrinkage, leading to excellent thermal insulation performance with low thermal conductivity (0.061 W/m·K). Also, the cross-linked aerogels are hydrophobic without using silylating reagents. This is helpful for large-scale production of aerogels for thermal applications.

Preparation of superhydrophobic and flexible polysiloxane aerogel

Silica aerogels, which consist of nano-particles and abundant nano-pores, have many outstanding properties. However, poor mechanical performances dramatically limit the practical applications of aerogel. Herein, we reported the preparation of novel superhydrophobic and flexible silica aerogel with several kinds of polysiloxane. The aerogel was formed with the polysiloxane and multimethoxy-POSS, the POSS was efficiently synthesized by thio-ene reaction and used as a crosslinking agent to strengthen the structure. The obtained data revealed all aerogels had the mesoporous structure (19–27 nm), high specific surface area (476.3–632.9 m2 g−1) and fine heat resistance. The different ratio of side groups on polysiloxane and the content of POSS led to the different mechanical properties, the ultimate compression strain was up to 50%. Moreover, the further oil-water separation application has also been demonstrated.

Durable Superhydrophobic Silica Aerogel Coating from Hydrophobic Gel Synthesis

Silica aerogel is a nanostructured porous solid material. It has a low bulk density, low thermal conductivity and can be hydrophobic. In this work, hydrophobic silica gel, a material used to form aerogel, is used instead of its powder form to avoid ultrafine air particles pollution. It is used to surface modified materials to make the materials superhydrophobic and still withstand physical abrasion that ordinary aerogel would not able to do. The superhydrophobic silica aerogel coating was designed by mixing the hydrophobic gel with DOW CORNING® 2405 resin as binder and varying DOWSIL™ Z-6137 silane and tetraethyl orthosilicate (TEOS). The coating is characterized by the static contact angles (CA) and abrasion test. Scanning electron micrographs of different coating compositions were investigated. Results show that the hydrophobic gel mixed with resin and Z-6137 silane have contact angle &gt;179º. Superhydrophobic silica aerogel coating can be utilized as material coatings for glass, fiber, polymer, etc.

Oil spills clean-up by super hydrophobic organo-modified silica aerogel monoliths treated by different solvents in ambient condition

Water-repellent silica aerogel with a high surface area and extremely low-density considered a very successful adsorbent for oil spills clean-up in the water surface treatment. The present work exhibits new route for the preparation of superhydrophobic organo-modified silica aerogel monoliths from tetraethoxysilane/vinyltriethoxysilane/Ethylene glycol (1:1:1 volume ratio) using sol-gel process and drying in ambient condition. The effects of different solvents (methanol, ethanol and propanol) in the solvent exchange step during the samples preparation procedure were studied. Characterization was performed by FT-IR, XRD, BET and SEM with EDX. The bulk density of the aerogel samples and contact angle of water droplet were measured. The as-prepared monolithic aerogel samples demonstrated a good adsorbing capacity (from 4.83–6.94 gram oil/gram aerogel) against two kind of commercial engines oils which have different specific weights.