Physical Aging of Single Wall Carbon Nanotube Polymer Nanocomposites: Effect of Functionalization of the Nanotube on the Enthalpy Relaxation

The glass-transition temperature and enthalpy relaxation of nanocomposites synthesized with low loadings of single wall carbon nanotubes (1 wt %) in poly(methylmethacrylate) (PMMA) have been investigated using differential scanning calorimetry (DSC). The results are compared with pure PMMA, and the effect of carbon nanotubes on the mobility of the polymer chain is discussed. Composites have been synthesized with unmodified nanotubes (SWNT/PMMA) as well as with amino-functionalized nanotubes (a-SWNT/PMMA) to provide a better interaction between the nanotube and the host matrix material. It was found that the glass-transition temperature of the unmodified nanocomposite SWNT/PMMA is the same as the neat PMMA (T-g=99 degrees C). A significant increase of 17 degrees C in the glass-transition temperature of the modified nanocomposite a-SWNT/PMM A is found when compared with the neat PMMA. Glass-transition results indicate that the presence of a-SWNT in PMMA restricts the segmental motion of the polymer chain. No significant change in activation energy of the enthalpy relaxation process or fragility index of PMMA is observed due to the addition of a-SWNT. However, a large broadening of the enthalpy peak is observed with the incorporation of SWNT in PMMA. This broadening leads to difficulty in the calculation of the activation energy and fragility index of SWNT/PMMA. Enthalpy relaxation behavior during isothermal aging is characterized at the same temperature with respect to the respective glass-transition temperatures of the three samples (at T-g and T-g - 2 degrees C (2 degrees C lower than the glass-transition temperature of each system)). The equilibrium enthalpy is reached at a shorter aging time in pure PMMA compared with SWNT/PMMA and a-SWNT/PMM A. The results obtained for enthalpy recovery show the signature of the restrictive environment of a-SWNT and SWNT on polymer chain mobility.