Analytical effective thermal conductivity model for colloidal porous composites and nanocomposites based on novolac/graphene oxide aerogels

The performance of porous composite materials in thermal energy storage and management applications can be engineered by controlling the relationship between the heat transfer mechanism and the structure of these materials. Analytical thermal conductivity models are essential tools to study and manage such structure/heat transfer relations in porous composite materials. This study develops an analytical thermal conductivity model for porous composites with colloidal matrix morphologies. The model developed here is a modified series-parallel model that considers important structural parameters such as the system's porosity, the colloidal size of the matrix, and the filler's aspect ratio. Moreover, essential effects in the structure of porous composites, including the gas-solid coupling effect and contact length of particles, are also included in the model developed here. In addition, this model can be used in a wide range of porosity and can predict the thermal conductivity of porous composites with appropriate accuracy by changing temperature, pressure, specific surface area, porosity, and other textural properties. Novolac/graphene oxide nanocomposite aerogels with different contents of graphene oxide (GO) nanosheets in the structure were prepared and used to study the validity of the data calculated using the developed model. Our results confirmed that the developed model in this study predicts the effective thermal conductivity of porous composite and nanocomposite structures with acceptable accuracy. More importantly, this model considers the structure's simultaneous presence of fillers and pores. As a result, it is an effective model for predicting the total thermal conductivity of porous composite and nanocomposite materials. Although the gaseous thermal conductivity contribution measured via the modified series-parallel model for porous composites (MSPC) model in novolac/graphene oxide nanocomposite aerogels decreased by around 79% with the incorporation of 15 wt.% GO, the effective thermal conductivity of nanocomposite aerogels was improved for more than 300%, compared to the neat novolac aerogel. Additionally, specific surface area and micropore surface area increased from 953.56 and 602.56 m(2)/g for neat novolac aerogel to 965.89 and 664.30 m(2)/g for the sample with 15 wt.% of GO respectively.

Automated summary

An analytical thermal conductivity model for porous composites with colloidal matrix morphologies was developed, which considers the simultaneous presence of fillers and pores in the structure. The model was validated using novolac/graphene oxide nanocomposite aerogels and showed acceptable accuracy in predicting the effective thermal conductivity. The model can be used to study and manage the structure/heat transfer relations in porous composite materials.