Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams

Apostolopoulou‐Kalkavoura, Varvara; Hu, Shiqian; Lavoine, Nathalie; Garg, Mohit; Linares, Mathieu; Munier, Pierre; Zozoulenko, Igor; Shiomi, Junichiro; Bergström, Lennart

doi:10.1016/j.matt.2020.11.007

Cited by 27 publications

(47 citation statements)

References 53 publications

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“…This behavior has been attributed to two competing effects: the humidity-induced swelling of the fibrillar foam walls causes the thermal boundary conductance between particle surfaces to decrease as the distance between them increases; whereas at higher humidity, the replacement of air by water in the interparticle spaces increases the thermal boundary conductance. 5 Nevertheless, even at 80% RH, the λ r of AIT CNF-MC-TA was below the thermal conductivity of typical polystyrene foams (30–40 mW m –1 K –1 ). 42 The λ r of AIT CNF-MC-TA was slightly lower than that of an analogous foam prepared with only 60% as much TA (AIT CNF-MC-LTA ; Figure S9 ) for all values of RH, which suggests that addition of TA did not increase λ r .…”

Section: Resultsmentioning

confidence: 94%

“…Further, moisture causes swelling in nanocellulose-based materials, increasing the distance between nanofibrils and thus phonon scattering and limiting thermal conductivity in aligned nanocellulose foams at moderate relative humidity. 5 …”

Section: Introductionmentioning

confidence: 99%

“…Nanocellulose-based foams and aerogels, in which large volumes of air are incorporated into scaffolds containing cellulose nanocrystals (CNC) or nanofibers (CNF), can have a thermal conductivity λ lower than that of air (26.2 mW m –1 K –1 at 295 K and 1 bar). , Anisotropic nanocellulose-based foams can have an especially low λ perpendicular to the aligned nanoparticles, − which has been attributed to the lower λ perpendicular to the cellulose chain and to phonon scattering at the interfaces. − Anisotropic foams are generated by directional ice templating, in which an aqueous suspension is frozen along a directional temperature gradient and then freeze-dried …”

Section: Introductionmentioning

confidence: 99%

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A Stiff, Tough, and Thermally Insulating Air- and Ice-Templated Plant-Based Foam

et al. 2022

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By forming and directionally freezing an aqueous foam containing cellulose nanofibrils, methylcellulose, and tannic acid, we produced a stiff and tough anisotropic solid foam with low radial thermal conductivity. Along the ice-templating direction, the foam was as stiff as nanocellulose–clay composites, despite being primarily methylcellulose by mass. The foam was also stiff perpendicular to the direction of ice growth, while maintaining λ r < 25 mW m –1 K –1 for a relative humidity (RH) up to 65% and <30 mW m –1 K –1 at 80% RH. This work introduces the tandem use of two practical techniques, foam formation and directional freezing, to generate a low-density anisotropic material, and this strategy could be applied to other aqueous systems where foam formation is possible.

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Section: Resultsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Stiff, Tough, and Thermally Insulating Air- and Ice-Templated Plant-Based Foam

et al. 2022

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“…Due to the wide range of applications of scaffolds produced by ice templating, a large number of research articles and reviews exist, [ 1–10 ] highlighting the increasing importance of this emerging process in recent years. Scaffolds with aligned porosity are highly interesting for various fields, from supercapacitors, [ 11–14 ] electrodes in batteries, [ 15,16 ] or thermal insulators [ 17,18 ] to biomaterials for tissue engineering, [ 19–22 ] 3D cell culture, [ 23 ] or as cell‐containing solid‐state scaffolds. [ 24 ]…”

Section: Introductionmentioning

confidence: 99%

Morphological Control of Freeze‐Structured Scaffolds by Selective Temperature and Material Control in the Ice‐Templating Process

et al. 2021

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Ice templating, also often referred to as freeze casting or freezestructuring, is a very straightforward, simple, low-cost, and versatile process for the fabrication of highly porous scaffolds with an anisotropic pore structure. Due to the wide range of applications of scaffolds produced by ice templating, a large number of research articles and reviews exist, [1][2][3][4][5][6][7][8][9][10] highlighting the increasing importance of this emerging process in recent years. Scaffolds with aligned porosity are highly interesting for various fields, from supercapacitors, [11][12][13][14] electrodes in batteries, [15,16] or thermal insulators [17,18] to biomaterials for tissue engineering, [19][20][21][22] 3D cell culture, [23] or as cell-containing solid-state scaffolds. [24] There are different ways of ice templating. [7] In the conventional unidirectional freezing method, a single temperature gradient is superimposed on the sample during freezing, whereby ice crystallization begins in a disordered manner on the cooled surface, resulting in a scaffold with an anisotropic structure in vertical direction and with several domains of different orientations in the horizontal plane. [25,26] A further possibility is bidirectional freezing, [26,27] where dual temperature gradients cause the ice to propagate both horizontally and vertically, resulting in a large-scale uniform scaffold structure. In addition, there are other approaches to influence the horizontal domain orientation, [7] such as radial, [28] magnetic, [29] electrical, [30] or ultrasonic freeze casting, [31] all of which lead to various morphologies of the resulting scaffolds and require different complex technical equipment. [7] This demonstrates the wide range of possibilities for the resulting scaffold morphology through the choice of an appropriate freezing process.A major advantage of unidirectional freezing is that this easyto-use process does not require complex and costly laboratory equipment. In general, a solution, suspension, or slurry is frozen in the presence of an external temperature gradient. Solutes are forced between the growing ice lamellae. After removal of the ice crystals by freeze drying, the scaffold represents a negative of the original ice morphology. [32] Consequently, a highly anisotropic porous sample is obtained. The morphological properties, such as vertical pore orientation or pore size of the scaffolds, play a decisive role depending on the application in which the scaffold is intended to be used. In terms of pore size, pores can be generated at different size scales, with pore diameters well above 100 μm being feasible. [33,34] Scaffolds, which are to be used as bone substitute materials in tissue engineering applications, may serve as an example. Values of at least 100 μm up to several hundred micrometers (> 300 μm) are considered optimal pore sizes for cell ingrowth, nutrient and

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“…(Solin et al 2020) Similarly, humidity-responsive chiral nematic CNC lms utilize the increase in the chiral nematic pitch of the helix with uptake of water to the change of color of the lm. (Chen et al 2020) Recently, it was also shown that moisture-induced swelling of CNM-based foams can also reduce the thermal conductivity due to enhanced phonon scattering (Apostolopoulou-Kalkavoura et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Moisture Uptake in Nanocellulose: The Effect of Relative Humidity, Temperature and Degree of Crystallinity

Garg

Apostolopoulou‐Kalkavoura

Linares

et al. 2021

Preprint

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Foams made from cellulose nanomaterials are highly porous and possess excellent mechanical and thermal insulation properties. However, the moisture uptake and hygroscopic properties of these materials need to be better understood for their use in biomedical and bioelectronics applications, in humidity sensing and thermal insulation. In this work, we present a combination of hybrid Grand Canonical Monte Carlo and Molecular Dynamics simulations and experimental measurements to investigate the moisture uptake within nanocellulose foams. To explore the effect of surface modification on moisture uptake we used two types of celluloses, namely TEMPO-oxidized cellulose nanofibrils and carboxymethylated cellulose nanofibrils. We find that the moisture uptake in both the cellulose nanomaterials increases with increasing relative humidity (RH) and decreases with increasing temperature, which is explained using the basic thermodynamic principles. The measured and calculated moisture uptake in amorphous cellulose (for a given RH or temperature) is higher as compared to crystalline cellulose with TEMPO- and CM-modified surfaces. The high water uptake of amorphous cellulose films is related to the formation of water-filled pores with increasing RH. The microscopic insight of water uptake in nanocellulose provided in this study can assist the design and fabrication of high-performance cellulose materials with improved properties for thermal insulation in humid climates or packaging of water sensitive goods.

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Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams

Cited by 27 publications

References 53 publications

A Stiff, Tough, and Thermally Insulating Air- and Ice-Templated Plant-Based Foam

A Stiff, Tough, and Thermally Insulating Air- and Ice-Templated Plant-Based Foam

Morphological Control of Freeze‐Structured Scaffolds by Selective Temperature and Material Control in the Ice‐Templating Process

Moisture Uptake in Nanocellulose: The Effect of Relative Humidity, Temperature and Degree of Crystallinity

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