Effects of free organic groups in carbon nanotubes on glass transition temperature of epoxy matrix composites

Molecular dynamics (MD) simulation and differential scanning calorimetric (DSC) test for epoxy resin composites embedded with carbon nanotubes (CNTs) were conducted to study effects of free organic groups in the CNTs on glass transition temperature (Tg) of the composites. Three types of CNTs including pristine, with hydroxyl (-OH) groups and carboxyl (-COOH) groups, respectively, were involved in the investigation. Both simulation and experimental results showed that Tgs of the CNT/epoxy composites are higher than that of the neat epoxy, Tgs of the composites randomly embedded with functionalized CNTs were lower than that with pristine CNTs, and Tg of the composites embedded with COOH-CNTs was much lower than that with OH-CNTs. This was attributed to the weaker interactions between the embedded functionalized CNTs and the polymer matrix, due to the further distances and larger inter-space around the CNTs caused by free -OH or -COOH groups in the CNTs.