"We have shown for the first time that you can take a packed nanoparticle bed that would typically act as an insulator, and by causing light to couple strongly into the material by engineering a high dielectric constant medium like water or ethylene glycol at the surfaces, you can turn the nanoparticle bed into a conductor," said Baratunde Cola, an associate professor at the Woodruff School of Mechanical Engineering at the Georgia Institute of Technology.
Nanoscale electromagnetic effects are created on the surface of the silicon dioxide particles and it is said that these effects could conduct the heat at higher efficiency than existing heat sink materials.
"Using the collective surface electromagnetic effect of the nanoparticles, the thermal conductivity can increase 20-fold, allowing it to dissipate heat," Cola added.
The researchers decided to experiment with these properties, first using water to coat the nanoparticles and turn the silicon dioxide nanoparticle bed into a conductor. But the water coating was not robust, so the researchers switched to ethylene glycol. It increased the heat transfer by a factor of 20 to approximately 1W/m-K, which is higher than the value ethylene glycol or silicon dioxide nanoparticles could produce alone, and competitive with expensive polymer composites used for heat dissipation.
Silicon dioxide was chosen because its crystalline lattice can generate resonant optical phonons at approximately room temperature.
"The resonance frequency, converted into the thermal radiation temperature for silicon dioxide, is around 50°C," said Cola. "With this material, we can turn on this effect at a temperature range that a microelectronic device is likely to see."
Though the ethylene glycol works well, it will eventually evaporate. For that reason, Cola plans to identify polymeric materials that could be adsorbed to the silicon dioxide nanoparticles to provide a more stable coating with a reasonable product lifetime. Further testing would be needed to ensure the long-term efficiency and to confirm that there are no impacts on the reliability of the electronic devices cooled with the technique, Cola concluded.
