Uniquely developing tunable morphologies and carbon nanotube localization in bi-phasic polymer blends by compatibilizer grafting

Abstract

The concentration of conducting fillers for rendering a continuous conductive pathway is referred to as the ‘electrical percolation threshold’. In this regard, the high aspect ratio of multiwalled carbon nanotubes (MWNTs) enables electrical percolation at lower concentrations. [1] Multiple successful attempts to reduce the electrical percolation threshold of MWNTs in insulating polymeric matrices are present in literature. We recently combined phase separation of polymer blends with selectively localized MWNTs [2] along with morphology refinement and stabilization by long random or block copolymers [3, 4] to reduce the electrical percolation threshold of MWNTs in PMMA/PαMSAN blends. We now present novel routes to simultaneously control the morphology and carbon nanotube network in phase separating 60/40 PMMA/PαMSAN blends. Hereto, different (co)polymers, including short PS polymers, long PMMA polymers and short PS-PMMA block copolymers with distinct molecular weight and asymmetry, are chemically grafted onto the surface of MWNTs. The intrinsic conductivity of the compatibilizer-grafted carbon nanotubes decreased by a decade due to the grafting procedure, thereby largely maintaining the beneficial electrical properties of MWNTs. In the blends, chemical grafting of (co)polymers onto the MWNTs simultaneously refined the blend’s morphology and steered the MWNT localization, as discerned from the dielectric relaxation spectra, thereby leading to some fascinating phenomena assisting long-ranged MWNT charge transfer at ultralow concentrations. In this regard, phase inversion, as verified by TEM images, leads to localization of MWNTs in the PαMSAN matrix with finely dispersed PMMA droplets, which facilitated charge transfer as connection or restriction points for the MWNT network in the matrix. The presence of interfacial MWNTs along the interface of small PMMA droplets further supports a continuous network of MWNTs in the blends. By chemical grafting, we could reduce the electrical percolation threshold of MWNTs from 0.5 wt% to 0.15 wt% in presence of very low compatibilizer concentrations (0.1 wt% instead of 2 wt% in the ungrafted case). We can thus conclude that a droplet-matrix morphology with tunable MWNT localization either in the matrix phase and/or at the blend interface is an effective alternative to bi-continuous morphologies for developing conductive blends. [1] I. Alig et al., Polymer, 53(1), 4-28 (2012) [2] S. Bose at al., Applied Materials and Interfaces, 2(3), 800-807 (2010) [3] A. Bharati at al., Polymer, 79, 271-282 (2015) [4] A. Bharati et al., Polymer, 108, 483-492 (2017)Conference talkstatus: publishe