Flexible and Transparent Silica Aerogels: An Overview

Parale, Vinayak G.,Lee, Kyu-Yeon,Park, Hyung-Ho The Korean Ceramic Society 2017 한국세라믹학회지 Vol.54 No.3

Silica aerogels are attracting attention due to certain outstanding properties such as low bulk density, low thermal conductivity, high surface area, high porosity, high transparency and flexibility. Due to these extraordinary properties of aerogels, they have become a promising candidate in thermal superinsulation. The silica-based aerogels are brittle in nature, which constrains their large scale-application. It is necessary to achieve transparency and flexibility of silica-based aerogels at the same time and with the same porous structure for optical field applications. Therefore, the present review focuses on the different sol-gel synthesis parameters and precursors in the synthesis of flexible as well as transparent silica aerogels. Also, a brief overview of reported flexible and transparent aerogels with some important properties and applications is provided.

Improvement in the high temperature thermal insulation performance of Y₂O₃ opacified silica aerogels

Parale, Vinayak G.,Jung, Hae-Noo-Ree,Han, Wooje,Lee, Kyu-Yeon,Mahadik, Dinesh B.,Cho, Hyung Hee,Park, Hyung-Ho Elsevier 2017 Journal of Alloys and Compounds Vol.727 No.-

<P><B>Abstract</B></P> <P>To improve the high-temperature thermal insulation characteristics of silica aerogels, it is important to reduce the radiative heat transfer. This can be achieved by Y<SUB>2</SUB>O<SUB>3</SUB> doping in the silica sol to opacify the infrared radiation of silica aerogels. The purpose of the present work was to study the effect of Y<SUB>2</SUB>O<SUB>3</SUB> incorporation on the structural and physicochemical properties of opacified silica aerogels prepared by a simple ambient pressure drying method. The influence of Y<SUB>2</SUB>O<SUB>3</SUB> addition on specific extinction coefficient and high temperature thermal insulation of prepared aerogels were investigated. The synthesized aerogels were lightweight and crack-free, with a granular, nanoporous morphology. The specific surface area, pore diameter, and bulk density of the prepared samples were 917.5–937.6 m<SUP>2</SUP>/g, 5.64–6.58 nm, and 0.047–0.076 g/cm<SUP>3</SUP>, respectively. The thermal conductivity of opacified silica aerogel at 1000 K was 0.080 W/(m.K), which was lower than the unopacified silica aerogel and it was around 0.104 W/(m.K) at same temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Low density Y<SUB>2</SUB>O<SUB>3</SUB> opacified SiO<SUB>2</SUB> aerogels by APD for HT thermal insulation. </LI> <LI> Y<SUB>2</SUB>O<SUB>3</SUB> effect on structural, physicochemical and morphological properties of aerogels. </LI> <LI> Aerogels: 917.5 m<SUP>2</SUP>/g surface area, 3.422 cm<SUP>3</SUP>/g pore volume, 6.58 nm pore diameter. </LI> <LI> 0.080 W/(m.K) of thermal conductivity of Y<SUB>2</SUB>O<SUB>3</SUB> opacified aerogels at 1000 K. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Ambient pressure dried tetrapropoxysilane-based silica aerogels with high specific surface area

Parale, Vinayak G.,Han, Wooje,Jung, Hae-Noo-Ree,Lee, Kyu-Yeon,Park, Hyung-Ho Elsevier 2018 Solid state sciences Vol.75 No.-

<P><B>Abstract</B></P> <P>In the present paper, we report the synthesis of tetrapropoxysilane (TPOS)-based silica aerogels with high surface area and large pore volume. The silica aerogels were prepared by a two-step sol-gel process followed by surface modification via a simple ambient pressure drying approach. In order to minimize drying shrinkage and obtain hydrophobic aerogels, the surface of the alcogels was modified using trichloromethylsilane as a silylating agent. The effect of the sol-gel compositional parameters on the polymerization of aerogels prepared by TPOS, one of the precursors belonging to the Si(OR)<SUB>4</SUB> family, was reported for the first time. The oxalic acid and NH<SUB>4</SUB>OH concentrations were adjusted to achieve good-quality aerogels with high surface area, low density, and high transparency. Controlling the hydrolysis and condensation reactions of the TPOS precursor turned out to be the most important factor to determine the pore characteristics of the aerogel. Highly transparent aerogels with high specific surface area (938 m<SUP>2</SUP>/g) and low density (0.047 g/cm<SUP>3</SUP>) could be obtained using an optimized TPOS/MeOH molar ratio with appropriate concentrations of oxalic acid and NH<SUB>4</SUB>OH.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Optically transparent and hydrophobic silica aerogel using TPOS was successfully synthesized. </LI> <LI> Sol-gel compositional effect using TPOS on the polymerization of aerogels was firstly reported. </LI> <LI> MeOH/TPOS and acid/base concentrations strongly influenced on the physical and textural properties. </LI> <LI> High surface area (938 m<SUP>2</SUP>/g) and low density (0.047 g/cm<SUP>3</SUP>) are obtained using TPOS as precursor. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile synthesis of hydrophobic, thermally stable, and insulative organically modified silica aerogels using co-precursor method

Parale, Vinayak G.,Lee, Kyu-Yeon,Jung, Hae-Noo-Ree,Nah, Ha-Yoon,Choi, Haryeong,Kim, Tae-Hee,Phadtare, Varsha D.,Park, Hyung-Ho Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.4

<P><B>Abstract</B></P> <P>Silica aerogels have low density and high specific surface area, but there are restrictions regarding their durability and commercialization owing to their fragile nature and the strong moisture absorbing behavior of the siloxane network. To overcome these restrictions, this study evaluated hybrid organically modified silica (ORMOSIL) aerogels by employing 3-(trimethoxysilylpropyl) methacrylate (TMSPM) in tetraethyl orthosilicate (TEOS) through a two-step sol-gel co-precursor method. The methacrylate organic groups were incorporated into the silica networks via reactions between the Si-OH moieties in silica aerogels, resulting in ORMOSIL aerogels. The properties of the ORMOSIL aerogels were strongly affected by the amount of TMSPM co-precursor. The highest concentration of TMSPM (30wt%) resulted in ORMOSIL aerogels with improved characteristics when compared with the pristine TEOS-based silica aerogels, such as hardness (0.15GPa), Young's modulus (1.26GPa), low thermal conductivity (0.038W/mK), high water contact angle (140°), and high thermal stability (350°C).</P>

Polypropylene/Silica Aerogel Composite Incorporating a Conformal Coating of Methyltrimethoxysilane-Based Aerogel

Choi, Haryeong,Parale, Vinayak G,Lee, Kyu-Yeon,Nah, Ha-Yoon,Driss, Zied,Driss, Dorra,Bouabidi, Abdallah,Euchy, Souhir,Park, Hyung-Ho American Scientific Publishers 2019 Journal of Nanoscience and Nanotechnology Vol.19 No.3

Flexible and lightweight Fe₃O₄/polymer foam composites for microwave-absorption applications

Phadtare, Varsha D.,Parale, Vinayak G.,Lee, Kyu-Yeon,Kim, Taehee,Puri, Vijaya R.,Park, Hyung-Ho Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.805 No.-

<P><B>Abstract</B></P> <P>Lightweight and highly porous magnetic polymer foam (MPF) composites were synthesized using a simple, efficient, and environmentally friendly strategy. Their scaffold structure was well controlled using a surfactant and by varying the amount of Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles (NPs) added to the emulsion solution used in their preparation. The three-dimensional (3D) sponge-like MPFs are microwave-absorbing materials, and their structural and microstructural characteristics were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The magnetic properties of the MPF composites were also characterized. The polymer matrix of the composites exhibited excellent thermal stability. The microwave-absorbing properties of the MPF composites with increasing amounts of Fe<SUB>3</SUB>O<SUB>4</SUB> NPs (5 wt%, 10 wt%, and 15 wt%) were systematically studied. The microwave absorption of the polymer foam was enhanced to as high as 82% with the addition of Fe<SUB>3</SUB>O<SUB>4</SUB> NPs. Our results demonstrate that the prepared MPF composites have the potential to be used as lightweight, microwave-absorbing materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Magnetic polymer foam was fabricated by high internal phase emulsion method. </LI> <LI> Fe<SUB>3</SUB>O<SUB>4</SUB> NPs provide magnetic properties without disturbing porous structure. </LI> <LI> The foam exhibited magnetic properties and compressibility. </LI> <LI> Microwave absorption was enhanced with macroporous polymer foam/Fe<SUB>3</SUB>O<SUB>4</SUB> composite. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Microwave dielectric properties of barium substituted screen printed CaBi₂Nb₂O₉ ceramic thick films

Phadtare, Varsha D.,Parale, Vinayak G.,Kulkarni, Gopal K.,Park, Hyung-Ho,Puri, Vijaya R. Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.7

<P><B>Abstract</B></P> <P>In the present study, Aurivillius-structured Ba<SUP>2+</SUP> substituted CaBi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> (CBNO) ceramic powder was synthesized by co-precipitation method. The CBNO thick films were delineated by screen printing method on alumina substrates using co-precipitated ceramic powder. The overlay method was adopted to measure the microwave dielectric properties of prepared thick films. Single phase layered perovskite structure of the prepared thick films was confirmed by X-ray Diffraction. The effects of Ba<SUP>2+</SUP> substitution on the surface morphology, bonding, and microwave dielectric properties of thick films were systematically presented. The maximum value of microwave dielectric constant for the CBNO thick films at 11.8GHz is 15.6 for Ba<SUP>2+</SUP>=0.8 substitution. The shift in the stretching vibration modes of the Nb-O bond of NbO<SUB>6</SUB> octahedron in the Raman spectra with a substitution of Ba<SUP>2+</SUP> in CBNO was observed. The substitution of Ba<SUP>2+</SUP> on A-site of CBNO improves the microwave dielectric properties of prepared thick films. This work may provide a new approach to enhance the microwave dielectric performance of Aurivillius-structured ceramic thick films.</P>

Molecular dynamics and experimental studies of nanoindentation on nanoporous silica aerogels

Patil, Sandeep P.,Parale, Vinayak G.,Park, Hyung-Ho,Markert, Bernd Elsevier Sequoia 2019 Materials science & engineering Structural materia Vol.742 No.-

<P><B>Abstract</B></P> <P>The nanomechanics during the indentation test on low-density nanoporous silica aerogels remains one of the least understood and explored areas of mechanics. In the present work, we performed nanoindentation using a spherical indenter on silica aerogels to investigate the mechanical properties, such as elastic modulus and hardness, and also, the deformation behaviour. Using all-atom simulations on large samples, the elastic modulus is computed from the elastic part of force–depth curves that can be fitted to the Hertz law, which shows that it increases with density. We proposed a novel approach to calculate the projected true contact area in nanoindentation and to estimate an accurate hardness of silica aerogel, which has a highly complex and randomly arranged network of atoms structure. The experimental studies of nanoindentation are performed on silica aerogel, which reveals that the measured elastic modulus is in good agreement with the simulations. However, the measured hardness values are nearly close to the projected contact area method. It suggests that in all-atom simulations the computed high hardness values using the proposed true area method are the actual local contact pressure. This new understanding may help to expand the use of computer simulations to explore the nanoindentation processes at the molecular level and to advance the macroscopic hardness calculation.</P>

Role of oxalic acid in structural formation of sodium silicate-based silica aerogel by ambient pressure drying

Nah, Ha-Yoon,Parale, Vinayak G.,Jung, Hae-Noo-Ree,Lee, Kyu-Yeon,Lim, Chang-Hyun,Ku, Yang Seo,Park, Hyung-Ho Springer-Verlag 2018 Journal of sol-gel science and technology Vol.85 No.2

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Enhanced microwave absorption of screen-printed multiwalled carbon nanotube/Ca_1−xBa_xBi₂Nb₂O₉ (0≤x≤1) multilayered thick film composites

Phadtare, Varsha D.,Parale, Vinayak G.,Kulkarni, Gopal K.,Park, Hyung-Ho,Puri, Vijaya R. Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.765 No.-

<P><B>Abstract</B></P> <P>Multiwalled carbon nanotube (MWCNT)/Ca<SUB>1−x</SUB>Ba<SUB>x</SUB>Bi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> (0 ≤ x ≤ 1)-layered thick film microwave-absorbing composites were prepared through the screen-printing method. The multilayered thick film composites were designed to improve their microwave absorption capabilities and the thickness of prepared thick films is around 115 μm. The layered thick film composites were synthesized with functionalized MWCNTs and co-precipitated Ca<SUB>1−x</SUB>Ba<SUB>x</SUB>Bi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> (0 ≤ x ≤ 1) (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) Aurivillius-type ceramics. The microwave absorption, transmission and reflection properties were investigated in the J, X, and Ku-bands with a frequency range of 6–18 GHz. The multilayered thick film composites showed enhanced microwave absorption properties in the broadband frequency region. The multilayered composite with x = 0.8 had 1.5 times better microwave absorption than the only MWCNT thick film. This work presents a new approach to the fabrication of multilayered composites with enhanced microwave absorbance via simple screen-printing method.</P> <P><B>Highlights</B></P> <P> <UL> <LI> MWCNT/Ca<SUB>1−x</SUB>Ba<SUB>x</SUB>Bi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> (0 ≤ x ≤ 1) layered thick film composites have been prepared via screen-printing method. </LI> <LI> Enhanced microwave absorption up to 88% was obtained due to the multilayered structure with thickness 115 μm. </LI> <LI> MWCNT/Ca<SUB>1−x</SUB>Ba<SUB>x</SUB>Bi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> (0 ≤ x ≤ 1) layered thick film composite shows broadband (6–18 GHz) microwave absorption characteristic. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>