Multiple assembly strategies for silica aerogel-fiber combinations – a review

Silica aerogels have a unique structure that makes them promising materials for variable applications. However, they are brittle due to weak inter-particle necks, and also expensive. Combining aerogel with fibers can not only enhance the mechanical/insulation properties, but also reduce dust release, and ease practical application. The majority of review articles in this field have been on the aerogel/textile systems' application or on textile impregnation in silica sol utilizing the sol–gel technique, with a few papers also addressing the use of aerogel as filler. This review for the first time highlights all strategies to assemble silica aerogel with textile materials. For sol–gel approaches, the fibers can be impregnated in a silica precursor sol to form the aerogel in situ between the fibers, but the sol itself can also be spun into aerogel fibers. Other strategies employ pre-formed silica aerogel, mixed in polymer or solvent matrices/slurries, to form aerogel injected blankets, aerogel-filled material coated fibers, and aerogel-filled composite fibers. Aerogel particles-filled textile packages have also been proposed. The emerging activities on simulations of aerogel-fiber combinations are reviewed. The advantages/disadvantages of various approaches are evaluated, and the current market situation and an outlook for the future of the field are summarized

Vývoj funkcionalizovaných vláknitých struktur

This habilitation thesis is a set of selected published scientific papers or engineering papers supplemented with a commentary according to §72 paragraph 3-point Act No. 111/1998 Coll. on universities. In total, the full set of scientific paper contains 24 research works published in impact factor journals and 2 published books. The chosen scientific papers are mainly focused on the study of fibrous structures for functional properties. The fibrous structures' peculiarities are explained where the important structural properties, such as porosity, are described. The possibilities of using different materials to boost selected functional properties are discussed. The development of nanoporous membranes by using electrospinning and electrospraying techniques are described. The efficacy of middle layers in multi-layered fibrous structures are detailed and embedding polyethylene glycol in silica aerogel, polytetrafluoroethylene fibrous layer filled with Aerogels and Phase Change Materials, aerogel-coated Kevlar Woven Fabrics, and PEG/Metal particle-coated viscose fabric is also described. The application of advanced structures for enhanced functionality is also provided. The conclusion summarizes this research topic's findings, benefits, and future direction.Tato habilitační práce je souborem vybraných publikovaných vědeckých prací nebo technických prací doplněných komentářem podle §72 odst. 3 písm. zákona č. 111/1998 Sb. o vysokých školách. Celkem soubor vědeckých prací obsahuje 24 vědeckých prací publikovaných v časopisech s impakt faktorem a 2 vydané knihy. Vybrané vědecké práce jsou zaměřeny především na studium vlákenných struktur z hlediska funkčních vlastností. Jsou vysvětleny zvláštnosti vlákenných struktur, kde jsou popsány důležité strukturní vlastnosti, jako je např. porózita. Jsou diskutovány možnosti využití různých materiálů pro zvýšení vybraných funkčních vlastností. Je popsán vývoj nanoporézních membrán pomocí technik elektrospinningu a elektrosprejování. Podrobně je popsána účinnost středních vrstev ve vícevrstvých vláknitých strukturách a zapouštění polyethylenglykolu do křemičitého aerogelu, polytetrafluorethylenová vlákenná vrstva plněná aerogely a materiály s fázovou změnou, kevlarové tkaniny potažené aerogely a viskózová tkanina potažená částicemi PEG/kovu. Je rovněž uvedena aplikace pokročilých struktur pro zvýšení funkčnosti vlákenných struktur. V závěru jsou shrnuty poznatky, přínosy a budoucí směřování tohoto výzkumného tématu

Aerogel Embedded High-performance Fibrous Materials

Vlákenné materiály jsou široce používány jako tepelné izolátory v různých aplikacích pro úsporu energie. Jejich tepelně izolační vlastnosti jsou omezeny, pokud je tloušťka materiálu omezena na několik milimetrů. V dnešní době je stále častěji kladen důraz na vývoj vysoce výkonných tepelně izolačních materiálů pro úsporu energie, zvýšení pohodlí, snížení nákladů a složitosti těchto systémů. Aerogel, který vykazuje vynikající tepelnou izolaci s extrémně nízkou tepelnou vodivostí, byl shledán jedním z nejatraktivnějších tepelně izolačních materiálů. Cílem této práce bylo vyvinout vysoce výkonný aerogel spojený s vlákennými materiály pro tepelnou izolaci a prověřit jeho výkon.Vrstvená nanovlákenná síťovina /aerogel /netkané materiály byly připraveny použitím laminovací metody s práškem s nízkým bodem tání jako tepelně spojujícím materiálem. Byl zkoumán účinek aerogelu a tepelného lepidla na tepelnou izolaci a propustnost vzduchu. V úvahu byl vzat sériový model pro tepelný odpor, byly porovnány a analyzovány teoretické předpoklady a naměřené výsledky. Bylo navrženo, že by měly být vzaty v úvahu nové techniky kombinující aerogel s vysoce porézními textiliemi s menším využitím pojivových materiálů.Nový aerogel obalený vlákenným materiálem bez použití jakéhokoliv pojivového materiálu, který spojuje částice aerogelu, byl vyvinut pomocí techniky laserového gravírování a laminovací metody. Pro měření tepelného výkonu byly použity termální kamera, zařízení Alambeta a KES-FT-II Thermolab. Byla provedena tlaková zkouška ke zkoumání kompresního zotavení, které určuje udržitelnost tepelné izolace. Dále bylo použito laboratorně vyráběné dynamické zařízení pro přenos tepla pro zjištění konvektivního tepelného chování těchto vícevrstvých materiálů, jakož i netkaných textilií obalených aerogelem, při různých rychlostech proudění vzduchu a zahřívání. Byly porovnány teplotní křivky v reálném čase z měření předehřátých podmínek. Byly vypočteny a posouzeny hodnoty teplotních rozdílů a konvektivního součinitele přestupu tepla za podmínek kontinuálního ohřevu. Zjištění by mohla přispět k novému vývoji pružných vysoce výkonných textilních materiálů se zabudovaným aerogelem pro průmyslové i oděvní aplikace.Pružné polyuretanové a polyvinylidenfluoridové nanoporézní membrány kombinované s aerogelem na bázi oxidu křemičitého byly připraveny elektrostatickým zvlákňováním. Tepelné vlastnosti a propustnost vzduchu byly hodnoceny a porovnávány. Byl učiněn závěr, že nanovlákna s aerogelem jsou vhodná pro tepelnou izolaci za chladného počasí. Tepelně izolační nosiče obsahující nanovlákna by mohly případně snížit hmotnost a objem tepelně ochranného oblečení.Pro provedení a vyhodnocování všech statistických výsledků byl v této práci použit statistický a analytický software Matlab_R2017a. Dosažené výsledky jsou významné a mohou být použity pro další studium v oblasti tepelných vlastností vysoko pevnostních vlákenných materiálů s aerogelem, které mohou být využity například pro tepelnou izolaci budov či ochranné oděvy.Fibrous materials are widely used as thermal insulators in various applications. Their thermal insulation ability is restricted when the material thickness is limited to few milli-meters. Nowadays, development of high-performance insulation materials to save energy consumption, increase comfort, decrease cost and complexity has drawn increasing attention. Silica aerogel, exhibiting superior thermal insulation performance with extremely low thermal conductivity, has been well acknowledged as one of the most attractive thermal insulating materials. The objective of this thesis was to develop aerogel embedded high-performance fibrous materials for thermal insulation application and investigate their performance.Layered nanofibrous web/silica aerogel/ nonwoven materials were prepared via laminating method by using low melting powder as thermal binding material. The effect of aerogel and thermal adhesive on thermal insulation performance and air permeability was examined. A series model was considered for thermal resistance, the theoretical predicted and measured results were compared and analysed. Results revealed that novel techniques to combine silica aerogel with high porous textiles with less use of binding materials should be considered.A novel aerogel-encapsulated fibrous material without using any binding material to bond aerogel particles was developed by using laser engraving technique and laminating method. Thermo Camera, Alambeta device and KES-FT-II Thermolabo were employed to measure thermal performance. Compression test was performed to examine the compression recovery which determines the sustainability of thermal insulation ability. Moreover, a laboratory-made dynamic heat transfer device was used to figure out convective thermal behaviour of these multi-layered materials as well as aerogel treated nonwovens under different airflow velocity and heating conditions. The real-time temperature curves of different materials were compared. The temperature difference and convective heat transfer coefficient under continuous heating condition were calculated and investigated. The findings could contribute to new developments in flexible aerogel-embedded high-performance textile materials for both industrial and clothing applications.Flexible polyurethane and polyvinylidene fluoride nanoporous membranes embedded with silica aerogel were prepared by electrospinning technique. Thermal properties and air permeability were evaluated and compared. It was concluded that nanofibers embedded with aerogel are good for thermal insulation in cold weather conditions. Thermal insulation battings incorporating nanofibers could possibly decrease the weight and bulk of current thermal protective clothing.Statistical analysis software, Matlab_R2017a were used to conduct all the statistical results in this study. The findings are significant and can be used for further study in the areas of aerogel embedded high-performance fibrous materials for thermal insulation in building, industrial and protective textile fields

Porous Ceramic Matrix Phase Change Composites for Thermal Control Purposes of Hypersonic Vehicle

Thermal control systems and heat insulation materials are required for a range of hypersonic vehicles ranging from ballistic reentry to hypersonic cruise vehicles, both within Earth’s atmosphere and non-Earth atmospheres. The combined thermodynamic/heat transfer relations of the phase change materials (PCMs) in silica nanoporous materials are developed to obtain mass, thickness, and temperature excursion as functions of percentage area of PCM under given maximum energy and thermal flux. The studies show that PCMs are one of the most preferred methods to thermal control applications that can effectively delay or modify the temperature rise of the surface of the aircrafts subjected to high thermal flux. This chapter also introduces the preparations of porous ceramic matrix phase change composite, putting PCMs to use in the internal thermal control materials for the hypersonic vehicles. Porous ceramic matrix serves as the supporting material, which provides structural strength and prevents the leakage of melted PCMs, and PCMs act as thermal absorb material limiting the temperature abruptly rising of the aircrafts. The structural pore properties of the silica matrix with different molar ratios of ethanol (EtOH)/tetraethoxysilane (TEOS) are investigated to determine suitable porous matrices for PCM. To adjust the pore structure of porous silica matrices with different molar ratios of EtOH and TEOS for PCM infiltration is mainly discussed. Furthermore, numerical and experimental studies are proposed to predict and investigate the thermal absorption characteristics of porous silica infiltrated with PCM for thermal control applications

Fabrication and characterization of a novel konjac glucomannan-based air filtration aerogels strengthened by wheat straw and okara

The konjac glucomannan (KGM)-based aerogel as an air filtration material was fabricated through sol-gel and freeze-drying methods. Results showed that gelatin and starch addition could increase the filtration efficiency and compressive strength of aerogel significantly, due to the appearance of more microporous structure and the formation of dense structure in aerogel. The addition of wheat straw could decrease the filtration resistance and increase the breathability of KGM-based aerogel, which was attributed to the multi-cavities of wheat straw. The aerogel with wheat straw had a filtration efficiency of 93.54% for particle matters ≥ 0.3 μm, a filtration resistance 29 Pa, and an air permeability 271.42 L/s·m2. Okara addition could increase the hydrophobicity of KGM-based aerogel by increasing the water contact angle and decreasing the equilibrium water content. The water contact angle of the aerogel containing okara reached 105.4°, and the equilibrium water content was decreased by 17.03%–81.10% compared with that without okara, with relative humidity 0%–80%. The results demonstrated that the KGM-based aerogel had good performance on filtration, mechanical and hydrophobic properties, indicating high potential application as an air filtration material

Incorporation of aerogel and phase change material in textiles for thermal protection

Protection against high heat conditions is of utmost importance in different specific fields, such as firefighting. The clothing of a firefighter is the last line of defence for survival. Though over time firefighters’ protective clothing (FPC) has improved significantly, still today firefighters receive severe burn injuries on duty. Hence, researchers all over the world continue to investigate innovative materials, methods and practices to improve the performance of FPC. Aerogel is an extremely heat-insulating material. It has very good potential to be used in FPC.The aim of this study is to explore the application potential of aerogel on textiles for thermal protection in high heat conditions, especially in firefighting. For the first time, the current study shows how the heat-insulating property of aerogel can be coupled with the heat-absorbing capability of phase change material (PCM) in FPC. PCMs are well known for their use in thermoregulating clothing because they are capable of absorbing and releasing heat as necessary. Aerogel was applied on the first layer of protection while PCM acted as a supportive layer from next to the skin surface. The combination has the capability of shielding the body from high heat and absorbing metabolic heat. An easy-to-apply coating additive was prepared by housing PCM in aerogels’ nanopores and a bench-scale instrument was developed to evaluate the radiation heat protection of various layers of FPC at the same time in a multilayer construction. The flammability risk of PCM-containing thermal liners has also been investigated. Finally, the study shows an innovative application of existing aerogel nonwoven in FPC and develops alternative methods to produce nonwoven fabric containing aerogel through needleless electrospinning

Thermal protection properties of aerogel-coated Kevlar woven fabrics

This paper investigated the thermal properties of aerogel-coated Kevlar fabrics under both the ambient temperature and high temperature with laser radiation. It is found that the aerogels combined with a Kevlar fabric contribute to a higher thermal insulation value. Under laser radiation with high temperature, the aerogel content plays a vital role on the surface temperature of the fabrics. At laser radiations with pixel time 330 μs, the surface temperatures of the aerogel coated Kevlar fabrics are 400-440°C lower than that of the uncoated fabric. Results also show that the fabric temperature is directly proportional to pixel time. It can be concluded that the Kevlar fabrics coated with silica aerogel provides better thermal protection under high temperature