Synergism in Binary (MWNT, SLG) Nano-carbons in Polymer Nano-composites: A Raman Study
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Synergism in Binary (MWNT, SLG) Nano-carbons in Polymer Nano-composites: A Raman Study
Peng Xu, James Loomis, Ben King and Balaji Panchapakesan University of Louisville, Louisville, KY 40208, U.S.A. ABSTRACT Load transfer and mechanical strength of reinforced polymers are fundamental to developing advanced composites. This paper demonstrates enhanced load transfer and mechanical strength due to synergistic effects in binary mixtures of nano-carbon/polymer composites. Different compositional mixtures (always 1 wt. % total) of multi-wall carbon nanotubes (MWNTs) and single-layer graphene (SLG) were mixed in polydimethylsiloxane (PDMS), and effects on load transfer and mechanical strength were studied using Raman spectroscopy. Significant shifts in the G-bands were observed both in tension and compression for single as well binary nanocarbon counterparts in polymer composites. Small amounts of MWNT0.1 dispersed in SLG0.9/PDMS samples (subscripts represents weight percentage) reversed the sign of the Raman wavenumbers from positive to negative values demonstrating reversal of lattice stress. A wavenumber change from 10 cm-1 in compression (-10% strain) to 10 cm-1 in tension (50% strain), and an increase in elastic modulus of ~103% was observed for MWNT0.1SLG0.9/PDMS with applied uniaxial tension. Presence of MWNTs in the matrix reduced the segmental polymeric chain length and provided limited extensibility to the chains. This in turn eliminated compressive deformation of SLG and significantly enhanced load transfer and mechanical strength of composites in tension. The orientation order of MWNT with application of uniaxial tensile strain directly affected the shift in Raman wavenumbers (2D band and G-band) and load transfer. It is observed that the cooperative behavior of binary nano-carbons in polymer composites resulted in enhanced load transfer and mechanical strength. Such binary compositions could be fundamental to developing advanced composites. INTRODUCTION An important application of graphitic nano-carbons is their use as reinforcers/fillers in polymer composites for enhanced mechanical strength and load transfer. In this respect, use of carbon nanotubes has been effective due to their high tensile strength, high aspect ratio [1-7]. Recently, two-dimensional (2D) graphitic nano-carbon, namely few layer graphene nanoplatelet (GNP), has shown impressive load transfer both in tension and compression when acting as reinforcers in polymer composites [8]. A surprising observation was that GNP fillers went into compression/tension under large uniaxial tensile/compressive deformation (>1.5%) [8]. This effect although intriguing is not yet well understood. Further, lack of clear understanding of how
mechanical strength and load transfer are affected in binary mixtures of nano-carbon/polymer composites warrants further investigation. Recent reports have shown extraordinary synergy in binary nano-carbon mixtures consisting of single wall carbon nanotubes (SWNT) and nano-diamonds (ND), and few layer graphene (FLG) and ND
