Carbon nanotube-induced structure and phase evolution in polymer-based nanocomposites crystallized at elevated pressures

The dispersion of small weight fraction of carbon nanotube (CNT) in Nylon 6,6 introduces a significant difference in the structure and phase evolution during crystallization at ambient and elevated pressures. In the nanocomposite, the γ-phase is promoted at low crystallization pressure of ∼0.1–25 MPa and is in striking contrast to pure Nylon 6,6, where γ-phase is nucleated only at crystallization pressures exceeding ∼50 MPa. The differences in the behavior of Nylon 6,6 and its nanocomposites is attributed to CNT–polymer interface driven nucleation, which is also responsible for significant reduction in spherulite size and increase in crystallinity. The nanoindentation behavior of the nanocomposite is assessed via nanoscale deformation experiments, which indicated that a significantly higher indentation-force is required for the Nylon 6,6–CNT nanocomposite as compared to Nylon 6,6 to produce a constant displacement. The observed significantly higher modulus and hardness is primarily CNT-induced effect. This observation is of particular relevance to functional devices because they are most likely to experience force in the nanonewton range, which can induce deformation at the micro- and/or nanometer scale.