Microscopic Mechanism of Tunable Thermal Conductivity in Carbon Nanotube-Geopolymer Nanocomposites

Geopolymer has been considered as a green and low-carbon material with great potential application due to its simple synthesis process, environmental protection, excellent mechanical properties, good chemical resistance, and durability. In this work, the molecular dynamics simulation is employed to investigate the effect of the size, content, and distribution of carbon nanotubes on the thermal conductivity of geopolymer nanocomposites, and the microscopic mechanism is analyzed by the phonon density of states, phonon participation ratio, spectral thermal conductivity, etc. The results show that there is a significant size effect in the geopolymer nanocomposites system due to the carbon nanotubes. In addition, when the content of carbon nanotubes is 16.5%, the thermal conductivity in carbon nanotubes vertical axial direction (4.85 W/(m k)) increases by 125.6% compared with the system without carbon nanotubes (2.15 W/(m k)). However, the thermal conductivity in carbon nanotubes vertical axial direction (1.25 W/(m k)) decreases by 41.9%, which is mainly due to the interfacial thermal resistance and phonon scattering at the interfaces. The above results provide theoretical guidance for the tunable thermal conductivity in carbon nanotube-geopolymer nanocomposites.