Structural behavior of cylindrical polystyrene-block-poly(ethylene-butylene)-block-polystyrene (SEBS) triblock copolymer containing MWCNTs: on the influence of nanoparticle surface modification

In this work, the influence of carbon nanotubes (CNTs) on the self-assembly of nanocomposite materials made of cylinder-forming polystyrene-block-poly(ethylene-butylene)-block-polystyrene (SEBS) is studied. CNTs are modified with polystyrene (PS) brushes by surface-initiated atom transfer radical polymerization to facilitate both their dispersion and the orientation of neighboring PS domains of the block copolymer (BCP) along modified CNT-PS. Dynamic rheology is utilized to probe the viscoelastic and thermal response of the nanoscopic structure of BCP nanocomposites. The results indicate that nonmodified CNTs increase the BCP microphase separation temperature because of BCP segmental confinement in the existing 3D network formed between CNTs, while the opposite holds for the samples filled with modified CNT-PS. This is explained by severely retarded segmental motion of the matrix chains due to their preferential interactions with the PS chains of the CNT-PS. Moreover, transient viscoelastic analysis reveals that modified CNT-PS have a more pronounced effect on flow-induced BCP structural orientation with much lower structural recovery rate. It is demonstrated that dynamic-mechanical thermal analysis can provide valuable insights in understanding the role of CNT incorporation on the microstructure of BCP nanocomposite samples. Accordingly, the presence of CNT has a significant promoting effect on microstructural development, comparable to that of annealing.