INFLUENCE OF THE CONCENTRATION OF CARBON NANOTUBES (CNT) ON THE THERMOPHYSICAL PROPERTIES OF EPOXY/CNT NANOCOMPOSITES AT LOW TEMPERATURES

The influence of the content of carbon nanofillers (multi- and single-wall nanotubes) on the thermophysical properties of epoxy nanocomposites was investigated on the temperature range from -150 to 150 degrees C. A plateau was found to exist in the concentration dependence of thermal conductivity on the concentration interval from 0.1 to 1.0 wt.% carbon nanotubes (CNTs). The thermal conductivity of the CNT composities exceeded that of pure epoxy resin by about 40%. A further increase in CNT content decreased the conductivity, owing to increasing interfaces between the two phases and the additional thermal resistance caused by phonon scattering on them. It is found that the temperature interval of transition of the composite from a glassy to a viscoelastic state greatly depends on the filler type and concentration. There exists a critical concentration at which a drop in the glass-transition temperature by 30% can be observed. The reason is the undercure of binder as a result of interaction between CNTs and epoxy macromolecules, which reduces the cross-linking density of structure of the polymer.