Simultaneous Improvement in Structural Properties and Microwave Shielding of Polymer Blends with Carbon Nanotubes

Precise control in dispersing nanostructured materials in a polymer blend structure is a key requirement in designing materials with tailor-made properties. In this study, the dispersion of a conducting additive (multiwalled carbon nanotubes, MWNTs) in a co-continuous polymer blend structure was controlled by introducing surface-active groups, which react in situ and localize in the thermodynamically nonpreferred phase. In addition, by modifying the MWNTs with a macromolecule, which is mutually miscible with the entities, the nanoscopic particles can be localized at the interface. This way, different MWNTs can be positioned in different phases under macroscopic processing conditions. Herein, we report that this unique strategy has led to simultaneous enhancement in both mechanical strength and electrical conductivity of the blend nanocomposites. In addition, intriguingly, the microwave shielding efficiency can also be tuned by this ordered arrangement of MWNTs in the blend structure in striking contrast to when the MWNTs are in the thermodynamically favored phase. An outstanding two-fold enhancement in the Young's modulus, as compared to control blends, and an impressive bulk electrical conductivity of 1 Sm-1 was noted for a particular blend structure wherein different MWNTs were positioned in different phases. In addition, the best blend structure designed here also exhibited a minimum reflection loss (RL) of approximately -61 dB and a shielding effectiveness of > 30 dB at 18 GHz. These data uncover the importance of polymer blends in designing lightweight electromagnetic interference (EMI) shielding materials.