Predicting the localization and interconnectivity of carbon nanotubes in compatibilized bi-phasic polymer blends

Abstract

Broadband dielectric spectroscopy (BDS) is often used to probe the electrical percolation threshold (EPT) of multiwalled carbon nanotubes (MWNTs) in polymeric systems. In this regard, phase separation of polymer blends with selectively localized MWNTs and stabilization of the cocontinuous morphology by block and random copolymers are valuable tools to reduce the EPT. We now present novel routes to simultaneously tune the phase-separated morphology and MWNT network in 60/40 PMMA/PαMSAN blends and thereby reduce the EPT. We developed a method based on BDS to successfully predict the localization and interconnectivity of MWNTs in the resulting conductive blends and validated our predictions by (S)TEM images. An improved dispersion and hence overall connectivity of MWNTs in solution mixed blends compared to melt mixed blends was discerned by comparing the electrical properties in the blends to that in equivalent PMMA and PαMSAN monophasic nanocomposites, thereby decreasing the EPT from 2 wt% in melt mixed blends to 0.5 wt% in solution mixed blends. Morphology stabilization and refinement were achieved by employing novel types of compatibilizers in solution mixed blends, including short PS-Br polymers and long PMMA-SH polymers, which further reduced the EPT from 0.5 wt% MWNTs to 0.15 wt% MWNTs in presence of 2 wt% of compatibilizer. The kinetic competition between the migration of the compatibilizers to the blend interface and the migration of the MWNTs to their energetically preferred PαMSAN phase during phase separation, gave rise to different MWNT localization, either in the PMMA phase, in the PαMSAN phase or at the interface, depending on the polymer compatibilizer. This in turn resulted in disparate interfacial polarization peak characteristics. The amount of entrapped polymer between adjacent MWNTs in the microcapacitor assembly was estimated by the dielectric interlayer model. The gap spacing of the microcapacitors, on the other hand, was deduced from the relaxation time of charge migration by fluctuation-induced tunnelling. Both these parameters allow to model the interfacial capacitance of the various MWNT microcapacitor networks in the compatibilized bi-phasic blends.status: publishe