Synergy among binary (MWNT, SLG) nano-carbons in polymer nano-composites: a Raman study

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 as binary nano-carbon counterparts in polymer composites. Small amounts of MWNT₀.₁ dispersed in SLG₀.₉=PDMS samples (subscripts represent 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 to 10 cm⁻¹ in tension, and an increase in elastic modulus of ~103% was observed for MWNT₀.₁SLG₀.₉=PDMS with applied uniaxial tension. Extensive scanning electron microscopy revealed the bridging of MWNT between two graphene plates in polymer composites. Mixing small amounts of MWNTs in SLG/PDMS eliminated the previously reported 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 such as nano-carbon based mixed dimensional systems.

Figure 1

SEM images of (a) MWNT₁SLG₀/PDMS, (b) MWNT₀SLG₁/PDMS, (c) MWNT_0.5SLG_0.5/PDMS, Scale bar: 500 nm. (d) Raman spectra of (a–c) samples, (e) Comparison of 2D peaks for pure SLG and SLG mixed in PDMS and small additions of MWNT to SLG/PDMS.

Figure 2

(a–c) SEM images of MWNT_xSLG_1-x/PDMS matrix, (d) schematic representation of SLG-MWNT/polymer system based on the SEM images above.

Figure 3

(a-1) & (b-1): Raman intensity versus shift in wavenumbers in uniaxial tension and compression for MWNT₁SLG₀ and MWNT₀SLG₁ respectively; (a-2) & (b-2) change in wavenumber versus strain in uniaxial tension and compression for MWNT₁SLG₀ and MWNT₀SLG₁ respectively

Figure 4

Load transfer (G-band) in SLG_0.9MWNT_0.1/PDMS: (a) Raman intensity versus wavenumber; (b) change in wavenumber as a function of percentage strain; and (c) change in wavenumber versus weight fraction of nano-carbon under 50% uniaxial tension.

Figure 5

(a) Model describing the change in orientation of the nanotube in polymer on application of a uniaxial tensile strain, (b) change in Raman wavenumbers for G and 2D band (measured) versus change in orientation angle (calculated) for different uniaxial tensile strains applied to the sample.

Figure 6

Full Width Half Maximum (FWHM) data for the different compositions of MWNT_xSLG_1-x/PDMS: (a) FWHM versus weight fraction of the nano-carbon; (b) change in FWHM versus percentage strain for MWNT₁SLG₀/PDMS; (c) change in FWHM versus strain for MWNT₀SLG₁/PDMS; and (d) change in FWHM versus strain for MWNT_0.1SLG_0.9/PDMS.

Figure 7

Elastic modulus versus weight percentage of nano-carbon filler for MWNT_xSLG_1-x/PDMS composite calculated using the rule of mixtures and compared to the experimental data.