ABSTRACT
Since solid-state heat transport in a highly porous nanocomposite strongly depends on the thermal boundary conductance (TBC) between constituent nanomaterials, further suppression of the TBC is important for improving performance of thermal insulators. Here, targeting a nanocomposite fabricated by stamping fumed silica nanoparticles, we perform a wide variety of surface functionalizations on fumed silica nanoparticles by a silane coupling method and investigate the impact on the thermal conductivity (Km). The Km of the silica nanocomposite is approximately 20 and 9 mW/m/K under atmospheric and vacuum conditions at the material density of 0.2 g/cm3 without surface functionalization, respectively, and the experimental results indicate that the Km can be modulated depending on the chemical structure of molecules. The surface modification with a linear alkyl chain of optimal length significantly suppresses Km by approximately 30%, and the suppression can be further enhanced to approximately 50% with an infrared opacifier. The magnitude of suppression was found to sensitively depend on the length of the terminal chain. The magnitude is also related to the number of reactive silanol groups in the chemical structure, where the surface modification with fluorocarbon gives the largest suppression. The surface hydrophobization merits thermal insulation through significant suppression of the TBC, presumably by reducing the water molecules that otherwise would serve as heat conduction channels at the interface. On the other hand, when the chain length is long, the suppression is counteracted by the enhanced phonon transmission through the silane coupling molecules that grow with the chain length. This is supported by the analytical model and present simulation results, leading to prediction of the optimal chemical structure for better thermal insulation.
ABSTRACT
Objective To study the thermal insulation properties of vacuum insulated panel(VIP)used as materials for blood transportation kits.Methods A VIP transportation kit was taken as test group,and a conventional transportation kit was taken as control.Phase change cool storage materials of the same amount and 4℃water bags were put into both kits.A recordable electronic thermometer was used to record the temperature within the two kits,and free hemoglobin(FHb)and potassium ion concentration were measured at 0, 4, and 7 days after blood storage.Results The temperature in the conventional transportation kit increased faster after 36 h, and was significantly higher than in the VIP transportation kit until 60 h.Besides,the VIP transportation kit kept the temperature under 10℃ for(60.7 ±0.6)h, compared to (54.2 ±3.0)h in the conventional transportation kit.FHb concentration was significantly lower in the VIP transportation kit[(605.26 ±74.63)mg/L]than in the conventional transportation kit[(1327.60 ±187.41)mg/L]at day 7(d 7),so was the potassium ion concentration in the VIP transportation kit[(22.7 ±0.4)mmol/L]compared to[(24.6 ±0.6) mmol/L]in the transportation kit at d 7.Conclusion The VIP transportation kit keeps the temperature under 10℃ for a longer time,and the blood quality of preservation is better than that of the conventional transportation kit.Novel heat preservation material can improve health support ability,and is of great value and significance.
