Thomas Coquil

Thermal conductivity of pure silica MEL and MFI zeolite thin films

This paper reports the room temperature cross-plane thermal conductivity of pure silica zeolite (PSZ) MEL and MFI thin films. PSZ MEL thin films were prepared by spin coating a suspension of MEL nanoparticles in 1-butanol solution onto silicon substrates followed by calcination and vapor-phase silylation with trimethylchlorosilane. The mass fraction of nanoparticles within the suspension varied from 16% to 55%. This was achieved by varying the crystallization time of the suspension. The thin films consisted of crystalline MEL nanoparticles embedded in a nonuniform and highly porous silica matrix. They featured porosity, relative crystallinity, and MEL nanoparticles size ranging from 40% to 59%, 23% to 47% and 55 nm to 80 nm, respectively. PSZ MFI thin films were made by in situ crystallization, were b-oriented, fully crystalline, and had a 33% porosity. Thermal conductivity of these PSZ thin films was measured at room temperature using the 3ω method. The cross-plane thermal conductivity of the MEL thin fi...

Thermal Conductivity of Sol-Gel Amorphous Mesoporous Silica Thin Films: Molecular Dynamics Simulations Versus Experiments

This study reports non-equilibrium molecular dynamics (MD) simulations predicting the thermal conductivity of amorphous mesoporous silica. The heat flux was imposed using the Muller-Plathe method and interatomic interactions were modeled using the van Beest, Kramer and van Santen (BKS) potential. First, simulations were validated against results reported in the literature for dense quartz and amorphous silica. The BKS potential was found to significantly overestimate the thermal conductivity of dense amorphous silica and results depended on the length of the simulation cell. Then, highly ordered pores were introduced in an amorphous silica matrix by removing atoms within selected areas of the simulation cell. Effects of the simulation cell length, pore size, and porosity on the thermal conductivity were investigated at room temperature. Results were compared with predictions from commonly used effective medium approximations as well as with previously reported experimental data for films with porosity and pore diameter ranging from 20% to 48% and 30 to 180 A, respectively. Predictions of MD simulations overestimated the experimental data and agreed with predictions from the coherent potential model. However, MD simulations confirmed that thermal conductivity in sol-gel amorphous mesoporous materials was independent of pore size and depended only on porosity.Copyright

Thermal Conductivity of Pure Silica MEL and MFI Zeolite Thin Films

This paper reports the room temperature cross-plane thermal conductivity of pure silica zeolite (PSZ) MEL and MFI thin films. PSZ MEL thin films were prepared by spin coating a suspension of MEL nanoparticles in 1-butanol solution onto silicon substrates followed by calcination and vapor-phase silylation with trimethylchlorosilane. The mass fraction of nanoparticles within the suspension varied from 16 to 55%. This was achieved by varying the crystallization time of the suspension. The thin films consisted of crystalline MEL nanoparticles embedded in a non-uniform and highly porous silica matrix. They featured porosity, relative crystallinity and MEL nanoparticles size ranging from 40 to 59%, 23 to 47% and 55 to 80 nm, respectively. PSZ MFI thin films were made by in-situ crystallization, were b-oriented, fully crystalline and had a 33% porosity. Thermal conductivity of the PSZ thin films was measured at room temperature using the 3ω method. The cross-plane thermal conductivity of the MEL thin films remained constant around 1.02 ± 0.10 Wm−1 K−1 despite increases in (i) relative crystallinity, (ii) nanoparticle size and (iii) yield as the nanoparticle crystallization time increased. Indeed, the effect of increases in these parameters on the thermal conductivity was compensated by the simultaneous increase in porosity. PSZ MFI thin films were found to have the same thermal conductivity as MEL thin films even though they had smaller porosity. Finally, the average thermal conductivity of the PSZ films was three to five times larger than that reported for amorphous sol-gel mesoporous silica thin films with similar porosity and dielectric constant.Copyright

Thermal Conductivity of Highly Ordered Amorphous and Crystalline Mesoporous Titania Thin Films

This paper reports the cross-plane thermal conductivity of amorphous and crystalline templated mesoporous titania thin films synthesized by evaporation-induced self-assembly. Both sol-gel and nanocrystal-based films were considered, with respective average porosities of 30% and 35%. The pore diameter ranged from 7 to 25 nm and film thickness from 60 to 370 nm while the average wall thickness varied from 3 to 25 nm. Nanocrystals in crystalline mesoporous films featured diameters between 9 and 13 nm. The thermal conductivity was measured at room temperature using the 3ω method. The experimental setup and the associated analysis were validated by comparing the thermal conductivity measurements with data reported in the literature for dense titania films with thickness ranging from 95 to 1000 nm. The cross-plane thermal conductivity of the amorphous mesoporous titania thin films did not show strong dependence on pore size, wall thickness, or film thickness. This can be attributed to the high atomic scale disorder of amorphous materials. Heat is thus mainly carried by localized non-propagating vibrational modes. The average thermal conductivity of the amorphous mesoporous titania films was identical to that of the nanocrystal-based films and equal to 0.37 W/m.K. Thermal conductivity of sol-gel crystalline mesoporous titania thin films was significantly larger than that of their amorphous counterparts. It also depended on the organic template used to make the films. The results indicated that the pore size was not an important factor. Instead thermal conductivity depended only on porosity, crystallinity, nanocrystal size and connectivity.Copyright

Thermal conductivity of cubic and hexagonal mesoporous silica thin films

No. % Uncertainty tf (nm) Min Max Min Max kf (W/m.K) Uncertainty 1 Hexagonal P123 46 ± 5 320 7 10 3 5 0.18 ± 0.02 2 Hexagonal P123 48 ± 5 160 7 10 3 5 0.18 ± 0.01 3 Hexagonal P123 40 ± 5 300 7 10 3 5 0.22 ± 0.01 4 Hexagonal P123 43 ± 5 540 7 10 3 5 0.20 ± 0.01 5 Hexagonal P123 45 ± 5 130 7 10 3 5 0.18 ± 0.01 6 Cubic Brij76 21 ± 5 155 3 5 2 3 0.30 ± 0.04 7 Cubic Brij76 23 ± 5 150 3 5 2 3 0.29 ± 0.02 8 Cubic Brij76 23 ± 5 170 3 5 2 3 0.34 ± 0.03 9 Cubic P123 29 ± 5 185 8 10 3 5 0.28 ± 0.03 10 Cubic P123 23 ± 5 200 8 10 3 5 0.38 ± 0.02 11 Cubic P123 26 ± 5 85 8 10 3 5 0.27 ± 0.01 12 Cubic P123 25 ± 5 80 8 10 3 5 0.27 ± 0.01 13 Cubic KLE 27 ± 5 300 15 18 10 12 0.35 ± 0.01 14 Cubic KLE 30 ± 5 130 15 18 10 12 0.32 ± 0.04 Matrix phase: Temperature: