Stress transfer in nanocomposites enabled by poly(methyl methacrylate) wrapping of carbon nanotubes

Abstract

Good dispersion and interfacial interaction of carbon nanotubes in polymer matrices are important to effectively achieve mechanical reinforcement in nanocomposites. Previously, it was shown that poly(methyl methacrylate) (PMMA) helically wraps around single wall carbon nanotubes (SWNTs), and thus prevents SWNT bundling. In this work, influence of PMMA-wrapped SWNTs on tensile properties of PMMA/SWNT composites and stress transfer from the matrix to the nanotubes were studied. The tensile modulus and tensile strength of the PMMA-wrapped SWNT nanocomposite buckypapers made by vacuum filtration are 5.9 and 3.7 times that of the SWNT buckypaper without PMMA wrapping, respectively. Stress transfer in SWNTs was determined by monitoring G′ Raman band shift during nanocomposite film tensile deformation. Results showed that during tensile deformation, PMMA-wrapped SWNTs in the nanocomposite buckypapers experienced up to 1 GPa stress, while negligible stress was observed in the SWNT buckypaper without PMMA wrapping. Solvent-cast nanocomposite films under tensile deformation, and with SWNT loading between 0.1 and 10 wt%, PMMA-wrapped SWNTs experience stress as high as 3.1 GPa, while nanocomposites made without PMMA wrapping experience only about half of this stress value. The improved tensile properties are a result of improved CNT dispersion and enhanced interfacial stress transfer achieved via PMMA wrapping of SWNTs. A new Raman band peak was observed at 2276 cm−1 in PMMA-wrapped nanocomposites. Dynamic mechanical properties of various nanocomposites were also studied and reported.