Thermal conductivity of porous silica films using modified polydimethylsiloxane and polyethyleneglycol as templates by sol–gel process

Dong, Dong; Xue, Wenjing; Liu, Xiaobo; He, Wei; Hu, Wencheng

doi:10.1016/j.micromeso.2011.02.006

Cited by 7 publications

(3 citation statements)

References 43 publications

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“…7,8 A limited number of studies have investigated the thermal conductivity of thin lms of mesoporous silica that oen have porosities of around 50%. 12,13 This is in contrast to more extensive studies of thermal conductivity on aerogels that have a porosity of 95-99%. 14 Their insulating properties arise from minimizing heat conduction by their low density and very complex and dissipative path for heat transfer through the solid fraction.…”

Section: Introductionmentioning

confidence: 93%

“…The mean free path value for air used here is 73.4 nm, and was determined using a temperature of 295 K and 1 atmosphere pressure (1.103 Â 10 5 Pa). For an average inner cell diameter of d pore ¼ 30.4 À 3.8 ¼ 26.8 nm, a Knudsen number of K foam cell n ¼ 2.74 is found using eqn (12). Then using a value of k air g ¼ 0.026 W m À1 K À1 we determine the gaseous conductivity of the foam cells to be k foam cell g ¼ 0.0028 W m À1 K À1 .…”

Section: Gaseous Conductivitymentioning

confidence: 99%

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A structural and thermal conductivity study of highly porous, hierarchical polyhedral nanofoam shells made by condensing silica in microemulsion films on the surface of emulsified oil drops

Mille¹,

Corkery²

2013

J. Mater. Chem. A

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Light-weight solid foams are utilized in applications such as packaging and insulation mainly due to their intrinsically high porosity, low relative density and associated mechanical and transport properties. Here hollow core spherical shells are prepared with walls made of a polyhedral silica nanofoam with open cells. A microemulsion film at the oil-water interface of oil droplets is used as a soft structural template for the condensation of soluble silica species. The microemulsion sets the length scale of the monodisperse silica nanofoam cells, and the emulsion droplets set the micron-scale dimensions of the polydisperse spherical shells. Porosity is achieved by removing the templates and oils, leaving pure lowdensity silica. This results in a hierarchically structured, highly porous shell foam material that packs into beds with a measured porosity of approximately 97.3%, well into the range of silica aerogels. Using a combination of electron microscopy, small-angle synchrotron X-ray diffraction and nitrogen physisorption, an accurate structural model for the nanofoam shells is constructed. The material is shown to be comprised of open-cell foams that are structurally analogous to dry polyhedral soap froths having minimal surface partitions, and Plateau boundaries. The primary polyhedral nanofoam cells are 30 nm in diameter connected by 7 nm cylindrical windows. These nanofoams form spherical monolithic shells with volume average mean diameter of 41 microns and shell thickness of 0.7 microns. Simple models for the thermal conductivity of these nanofoam shell materials are constructed that include accounting for the nanoscale effects on gaseous and solid thermal conductivity. These are compared to the measured value of 0.041 W m À1 K À1 . These materials represent new structures in the family of selfassembled, highly porous silica materials and are potentially useful in packaging and insulation and other applications due to their light weight and/or intrinsically low thermal conductivity and associated mechanical and transport properties.

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Section: Introductionmentioning

confidence: 93%

Section: Gaseous Conductivitymentioning

confidence: 99%

A structural and thermal conductivity study of highly porous, hierarchical polyhedral nanofoam shells made by condensing silica in microemulsion films on the surface of emulsified oil drops

Mille¹,

Corkery²

2013

J. Mater. Chem. A

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“…In the nanoreactor, the inner AuNPs are the unique thermal sources. Since their thermal conductivity (κ gold = 318 W m −1 K −1 ) is also far larger than those of the other components (κ solvent = 0.6 W m −1 K −1 , κ silica = 0.05 W m −1 K −1 ), 21 we can consider the temperature uniform for the AuNPs. 22 These calculations show that, while the temperature inside the reactor increases 90 °C, thermal heating of the exterior bulk solution is almost inhibited.…”

mentioning

confidence: 99%

Nanoreactors for Simultaneous Remote Thermal Activation and Optical Monitoring of Chemical Reactions

Vázquez-Vázquez¹,

Vaz²,

Giannini

et al. 2013

J. Am. Chem. Soc.

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We report herein the design of plasmonic hollow nanoreactors capable of concentrating light at the nanometer scale for the simultaneous performance and optical monitoring of thermally activated reactions. These reactors feature the encapsulation of plasmonic nanoparticles on the inner walls of a mesoporous silica capsule. A Diels-Alder cycloaddition reaction was carried out in the inner cavities of these nanoreactors to evidence their efficacy. Thus, it is demonstrated that reactions can be accomplished in a confined volume without alteration of the temperature of the bulk solvent while allowing real-time monitoring of the reaction progress.

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Enhanced Luminescence, Collective Heating, and Nanothermometry in an Ensemble System Composed of Lanthanide‐Doped Upconverting Nanoparticles and Gold Nanorods

Rohani

Quintanilla

Tuccio

et al. 2015

Advanced Optical Materials

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A combined system of gold nanorods and NaGdF 4 :Er 3+ /Yb 3+ upconverting nanoparticles with double functionality, luminescence enhancement, and monitored heating is introduced. The paired nanostructures could become an excellent optical heater with thermal probe incorporated. To study their interaction, the longitudinal surface plasmon resonance of the gold nanorods is tuned to 980 nm, in resonance with the Yb 3+ absorption wavelength, so they can be simultaneously excited. Gold nanorods create a localized electromagnetic fi eld that enhances the emission intensity from upconverting nanoparticles. This luminescence enhancement is shown to depend on the interparticle distance and excitation power and, in this system, reaches a maximum enhancement of 9 for the green emission of Er 3+ ions. At the same time, evidence of strong collective heating from the gold nanorods is demonstrated. The temperature can be controlled by changing the excitation power and measured in situ via the Er 3+ thermally sensitive luminescence. At high excitation powers, the heating can trigger a deformation of the gold nanorods, which limits the maximum temperature achievable in the system to 160 °C. Combining these nanostructures provides an all-optical heating system with improved emission intensity that can monitor the temperature achieved.

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Thermal conductivity of porous silica films using modified polydimethylsiloxane and polyethyleneglycol as templates by sol–gel process

Cited by 7 publications

References 43 publications

A structural and thermal conductivity study of highly porous, hierarchical polyhedral nanofoam shells made by condensing silica in microemulsion films on the surface of emulsified oil drops

A structural and thermal conductivity study of highly porous, hierarchical polyhedral nanofoam shells made by condensing silica in microemulsion films on the surface of emulsified oil drops

Nanoreactors for Simultaneous Remote Thermal Activation and Optical Monitoring of Chemical Reactions

Enhanced Luminescence, Collective Heating, and Nanothermometry in an Ensemble System Composed of Lanthanide‐Doped Upconverting Nanoparticles and Gold Nanorods

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