A molecular dynamics simulation of the glass transition temperature and volumetric thermal expansion coefficient of thermoset polymer based epoxy nanocomposite reinforced by CNT: A statistical study

Abstract

A molecular dynamics simulation study is performed to predict the glass transition temperature ( Tg) and the volumetric coefficient of thermal expansion (CTE) of thermoset polymer based nanocomposite reinforced by carbon nanotube (CNT). An atomistic model of cross-linked Diglycidyl ether bisphenol A (DGEBA) epoxy and Diethylenetriamine (DETA) was built as a matrix by employingCondensed-phase optimized molecular potentials for atomistic simulation (COMPASS27) force field. Different molecular models were constructed with various types of CNT embedded in epoxy simulation boxes. Tg was determined based on density variation with temperature. Furthermore, a new method is proposed to compute the CTE based on density variation with temperature. The effects of CNT diameter, volume fraction and chirality on Tg and CTE of nanocomposites were investigated using molecular dynamics simulation. For all cases, studied and CTE were less than pure epoxy (between 3.77% to 10.05% for Tg and respectively 14.24% to 32.23% and 23.82% to 41.65% for CTE below and above of Tg ). Increasing the CNT diameter in nanocomposite increases Tg and CTE (5.0% for Tg and 20.0% for CTE when the diameter of CNT changed 7.8A0 to 15.6A0). On the other hand increasing volume fraction of CNT in the nanocomposite decreases Tg and CTE (2.7% for Tg and 13.8% for CTE when the volume fraction of CNT in the nanocomposites changed 3.36% to 5.23%). Chirality studies under constant weight fraction of nanocomposites show that applying armchair CNT instead of zigzag CNT, decreases Tg and increases CTE (2.1% for Tg and 5.8% for CTE)