Controlling Thermal Conductivity in Mesoporous Silica Films Using Pore Size and Nanoscale Architecture

Abstract

This work investigates the effect of wall thickness on the thermal conductivity of mesoporous silica materials made from different precursors. Sol–gel- and nanoparticle-based mesoporous silica films were synthesized by evaporation-induced self-assembly using either tetraethyl orthosilicate or premade silica nanoparticles. Since wall thickness and pore size are correlated, a variety of polymer templates were used to achieve pore sizes ranging from 3–23 nm for sol–gel-based materials and 10–70 nm for nanoparticle-based materials. We found that the type of nanoscale precursor determines how changing the wall thickness affects the resulting thermal conductivity. The data indicate that the thermal conductivity of sol–gel-derived porous silica decreased with decreasing wall thickness, while for nanoparticle-based mesoporous silica, the wall thickness had little effect on the thermal conductivity. This work expands our understanding of heat transfer at the nanoscale and opens opportunities for tailoring the thermal conductivity of nanostructured materials by means other than porosity and composition.

Examining the Role of Atomic Scale Heterogeneity on the Thermal Conductivity of Transparent, Thermally Insulating, Mesoporous Silica–Titania Thin Films

“…The data show that adding either 10 or 20 mol % titania resulted in reduced thermal conductivity compared to the pure silica films, presumably because all Ti incorporation provides additional centers that scattered propagons and diffusons, thus reducing the thermal conductivity of those samples, regardless of the compositional homogeneity. In agreement with this idea, PWSM fits to pure silica samples, published previously, produce a value of x = 0.31, which is higher than any of the titania-containing samples . This suggests that all titania incorporation frustrates parallel heat conduction.…”

“…In agreement with this idea, PWSM fits to pure silica samples, published previously, produce a value of x = 0.31, which is higher than any of the titania-containing samples. 26 This suggests that all titania incorporation frustrates parallel heat conduction. When we further compare all the samples that show titania clustering, that is, the ST10reg sample and all ST20 samples, we observe that the ST20 samples had lower thermal conductivities than the ST10reg samples.…”

“…Many structural effects on thermal conductivity in templated mesoporous materials have already been reported, such as the role of precursor type (discrete nanocrystals vs continuous sol–gel), wall thickness, and pore packing (cubic vs hexagonal). − In nontemplated porous silica, the fractal dimension has also been shown to influence the thermal conductivity. − …”

Copper deposited diatom-biosilica with enhanced photothermal and photodynamic performance for infected wound therapy

“…It has been reported that the thermal conductivity of porous silica could be lower than 0.098 W mK À1 . 44 The 808 nm near-infrared laser was a thermal light source, and it produced heat in the irradiation process. The low thermal conductivity of DBs was conducive to reducing heat loss through self-insulation, which made the temperature of DBs also increase under laser irradiation.…”

Understanding the Effect of Nanoparticle Size on Thermal Conductivity in Amorphous Nanoporous Materials Made from Colloidal Building Blocks

“…The kinetic theory relates the thermal conductivity of bulk silica κ SiO 2 to the phonon mean free path λ such that κ SiO 2 = 1 3 ρ SiO 2 c v , SiO 2 ν λ . Here, ρ SiO 2 is the density of silica (=2210 kg m –3 ), c v ,SiO 2 is our previously measured specific heat capacity at constant volume (=750 J kg –1 K –1 ), , and v is the average sound velocity in the material, obtained from the longitudinal v l and transversal v t wave vectors given by v = 1 3 v normall + 2 3 v normalt , with v l = 5968 m s –1 and v t = 3764 m s –1 . From this kinetic model, a phonon mean free path of λ = 0.56 nm in bulk silica (κ SiO 2 = 1.4 W m –1 K –1 ) was retrieved, which agrees reasonably well with the value of λ = 0.42 nm that was obtained from eq .…”