Investigation of size effects on the thermal conductivity of materials with micro to nanoscale structure

The effect of small- (micro to nano) scale structure on thermal conductivity was observed through measurements of the effective thermal conductivity of bulk samples with small-scale structure. The effective thermal conductivity of ivory, a natural nanocomposite, was found to be low, less than would be expected for a composite of the same composition built from macro-size units. Thermal conductivity measurements and the application of a literature model for filler/matrix composites suggest that size effects on thermal transport are of practical importance in optimizing the thermal properties of light-cured dental materials. A finite element model shows the importance of low thermal conductivity to protecting the tooth pulp. A size effect also was observed from measurements on polycrystalline zeolite NaX. Significantly lower thermal conductivity was found for a sample with 800 nm particles in comparison to 2 mum particles. No corresponding reduction was observed for a sample with 20--100 nm particles.