Evaluation Of Thermal Conductivity Of Amorphous Materials Based On The Excluded Volume Theory

Amorphous materials are ubiquitous in modern industry owing to their unique structures and properties.An in-depth understanding of thermal transport in amorphous materials and the prediction of their thermal conductivity are not only of great importance in theory,but also beneficial to better design and engineer materials with required thermal properties.In this paper,a prediction model of thermal conductivity of amorphous materials is established,which can predict the thermal conductivity of many amorphous materials.The research development for thermal conductivity of amorphous materials is summarized,which demonstrates that the molecular-level weak interaction is the main factor limiting the thermal conductivity of amorphous materials.Moreover,the weak interaction can be regarded as the contact thermal resistance between the fundamental units to further study.Based on the assumption,the complex network theory and the thermal resistance network model are adopted to describe the heat transfer among the fundamental units in amorphous materials.And the excluded volume theory is applied to estimate the average number of contacts for the fundamental units.Then,the thermal conductivity prediction model of amorphous materials is deduced,and the specific formulas of various materials are obtained by choosing the fundamental units carefully.In the research of traditional amorphous materials,the model can predict the thermal conductivity of most liquids,which are generally with only relatively weak intermolecular interactions,and the calculated results are near the same as the experimental values.In addition,the model also shows a good prediction performance in predicting the thermal conductivity of methanol and four alkane liquids under various temperatures.The thermal conductivity of isomers,as well as alkane liquids,varies due to molecular structural changes,and the influence of resulting shape parameters’ changes can be reflected by the variations in the excluded volume.As for amorphous solids and amorphous polymers,the predicted results from the model are still in good agreement with the experimental values.In the research of novel amorphous materials,the model can predict the thermal conductivity of single-walled carbon nanotube(SWCNT)networks,and the calculated results are close to the experimental values.Furthermore,the model explains well the experimentally reflected independent relationship between the thermal conductivity of SWCNT networks and the length of SWCNTs.The validity of applying the model to multi-walled carbon nanotube(MWCNT)networks is also initially verified by checking the contact thermal conductance obtained by reverse calculation.The model is used to predict the thermal conductivity of carbon nanotube(CNT)networks as a function of density,and the results reveal that the threedimensional random CNT networks behave more like thermal insulators rather than thermal conductors.Additionally,the model can calculate the thermal conductivity of nanoparticlepacked beds within experimental uncertainty in some cases.The successful application of the model to the thermal conductivity prediction of different amorphous materials further confirms the dominant effect of the thermal resistance among fundamental units in the thermal transport within these materials.Besides,the model also provides a simple and effective prediction method for the subsequent study of the thermal conductivity of amorphous materials.