Continuous adjustment of fractal dimension of silica aerogels

Li, Tiemin; Du, Ai; Zhang, Ting; Ding, Wenhui; Liu, Mingfang; Shen, Jun; Zhang, Zhihua; Zhou, Bin

doi:10.1016/j.jnoncrysol.2018.07.026

Cited by 16 publications

(13 citation statements)

References 37 publications

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“…For example, significant changes in the fractal and Porod regions were found for wet and dry gels, and correlated to different network features 23 . Furthermore, a change in the fractal region was attributed to the aging of aerogels 24 .…”

Section: Introductionmentioning

confidence: 99%

Springback effect and structural features during the drying of silica aerogels tracked by in-situ synchrotron X-ray scattering

Zemke

Scoppola

Simon

et al. 2022

Sci Rep

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The springback effect during ambient pressure drying of aerogels is an interesting structural phenomenon, consisting of a severe shrinkage followed by almost complete re-expansion. The drying of gels causes shrinkage, whereas re-expansion is believed to be linked to repelling forces on the nanoscale. A multi-scale structural characterization of this significant volume change is key in controlling aerogel processing and properties. In this work, hydrophobic, monolithic silica aerogels with high specific surface areas were synthesized by modification with trimethylchlorosilane and ambient pressure drying. Here, we report a multi-method approach focusing on in-situ X-ray scattering to observe alterations of the nanostructured material during the drying of surface-modified and unmodified silica gels. Both show a porous fractal nanostructure, which partially collapses during drying and only recovers in surface-modified samples during the springback effect. Distinct changes of the X-ray scattering data were reproducibly associated with the shrinkage, re-expansion and drying of the gel network. Our findings may contribute to tailor aerogels with specific functionality, as the springback effect has a direct influence on properties (e.g., porosity, pore size distribution), which is directly affected by the degree of re-expansion.

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Section: Introductionmentioning

confidence: 99%

Springback effect and structural features during the drying of silica aerogels tracked by in-situ synchrotron X-ray scattering

Zemke

Scoppola

Simon

et al. 2022

Sci Rep

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“…According to IUPAC definition, aerogel is a 3‐D porous solid nano dimension structure made of open micropores, for which the pores are filled with a common gas such as air 1 and has a super high specific surface area along with high potential for various applications 2 . In accordance with morphological research studies, organic aerogels structure consists of secondary particles with geometries close to sphere, each of which is composed of a large number of primary particles, 3,4 for which presence of primary and secondary particles leads to pores formation in various dimensions 5 . By virtue of internal nanoporous microstructure, it would be hardly possible to predict, design, and optimize such microstructure heat transfer phenomena to attain precise thermal analysis to a large extent.…”

Section: Introductionmentioning

confidence: 83%

“…2 In accordance with morphological research studies, organic aerogels structure consists of secondary particles with geometries close to sphere, each of which is composed of a large number of primary particles, 3,4 for which presence of primary and secondary particles leads to pores formation in various dimensions. 5 By virtue of internal nanoporous microstructure, it would be hardly possible to predict, design, and optimize such microstructure heat transfer phenomena to attain precise thermal analysis to a large extent. To achieve a deep understanding of the mathematical relation among insulation properties, thermal diffusion, and aerogels microstructure, thermal conductivity prediction models such as experimental, 6 quasiexperimental, 7 numerical, and analytical 8 have been proposed.…”

Section: Introductionmentioning

confidence: 99%

Novolac aerogel thermal diffusion and efficiency enhancement using paraffin wax core/polyurethane shell phase‐change material nanocapsules

Abdeali

Bahramian

2021

Intl J of Energy Research

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Summary Aerogels are one of the most promising nano‐dimension open‐cell foams with considerably varied characteristics such as high porosity, super large specific surface area, low density, and super low thermal conductivity. Aerogel's high porosity and microstructure consisting of micro‐ and nanoparticles as well as pores in nanometer dimension are the origin of distinctive properties. However, the main challenge of aerogels is their low density (0.05−0.50 gcm3), which leads to equal thermal diffusion (normalα×10−7) compared with general thermal insulators. To minimize aerogel thermal diffusion and to enhance thermal insulation, replacing some aerogel colloids with phase‐change material nanocapsules (NPCMs) (while aerogel IUPAC definition and at least porosity of 80% is preserved) is proposed in this work. While NPCMs undergo a physical change during phase transfer, temperature becomes persistent, and as a consequence, specific heat capacity (Cp) getting close to an infinite number and thermal diffusion (normalα=knormalρCp) will tend to very low values. Results have demonstrated that by only applying 4.5 wt.% of paraffin wax core /polyurethane shell (PW/PU) NPCMs instead of some novolac aerogel colloids, aerogel has experienced temperature decrement as well as stability. During NPCMs' melting process, thermal diffusivity has reached 2.5×10−12 and temperature increment delay rate has become 40%.

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“…10 Other examples include fractal-shaped graphene 11 and silica aerogels. 12 In these reports, the growth of fractal structures occur generally in solution or on infinitely large substrates; it is difficult to obtain fractal nanoparticles with both uniform sizes and tunable fractal structures.…”

Section: ■ Introductionmentioning

confidence: 99%

Fractal-in-a-Sphere: Confined Self-Assembly of Fractal Silica Nanoparticles

Jiao

Song

et al. 2019

Chem. Mater.

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Fractal objects such as snowflakes and trees are ubiquitous in nature. However, fractal nanoparticles with uniform morphology and controllable structures are difficult to make. Herein, using a fractal-in-a-sphere strategy, we report the confined self-assembly of fractal silica nanoparticles with tunable fractal generations and uniform sizes. One advantage of controllable fractal generations has been demonstrated in enzyme delivery for parasite oocyst control. The fractal silica nanoparticles exhibited better oocysticidal performance compared with nanoparticles of other structures due to combined effects of enhanced adhesion, penetration across the oocyst wall, and high local enzyme concentrations. This study paves the way for the fabrication of fractal silica nanoparticles with fine structures and versatile applications.

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Continuous adjustment of fractal dimension of silica aerogels

Cited by 16 publications

References 37 publications

Springback effect and structural features during the drying of silica aerogels tracked by in-situ synchrotron X-ray scattering

Springback effect and structural features during the drying of silica aerogels tracked by in-situ synchrotron X-ray scattering

Novolac aerogel thermal diffusion and efficiency enhancement using paraffin wax core/polyurethane shell phase‐change material nanocapsules

Fractal-in-a-Sphere: Confined Self-Assembly of Fractal Silica Nanoparticles

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