Near-Edge X-ray Absorption Fine Structure Studies of Electrospun Poly(dimethylsiloxane)/Poly(methyl methacrylate)/Multiwall Carbon Nanotube Composites

Abstract

This work describes the near conduction band edge structure of electrospun mats of MWCNT-PDMS-PMMA by near edge X-Ray absorption fine structure (NEXAFS) spectroscopy. Effects of adding nanofillers of different sizes were addressed. Despite observed morphological variations and inhomogeneous carbon nanotube distribution, spun mats appeared homogeneous under NEXAFS analysis. Spectra revealed differences in emissions from glancing and normal spectra; which may evidence phase separation within the bulk of the micron-size fibers. Further, dichroic ratios show polymer chains did not align, even in the presence of nanofillers. Addition of nanofillers affected emissions in the C-H, C=O and C-C regimes, suggesting their involvement in interfacial matrix-carbon nanotube bonding. Spectral differences at glancing angles between pristine and composite mats suggest that geometric conformational configurations are taking place between polymeric chains and carbon nanotubes. These differences appear to be carbon nanotube-dimension dependent, and are promoted upon room temperature mixing and shear flow during electrospinning. CH-π bonding between polymer chains and graphitic walls, as well as H-bonds between impurities in the as-grown CNTs and polymer pendant groups are proposed bonding mechanisms promoting matrix conformation.

Tomography of Electrospun Carbon Nanotube Polymeric Blends by Focus Ion Beam: Alignment and Phase Separation Analysis from Multicontrast Electron Imaging

“…However, for this system, alignment has been thoroughly discussed in early works through synchrotron spectroscopies. Dichroic ratio studies suggested that macromolecules did not align, which is consistent with the referred works, since no additional electric field was used upon collection …”

“…In fact, on those earlier reports, we have discussed the impact that electrospinning bears on both CNT alignment and bonding dynamics . Indeed, electrospinning has proved successful in the promotion of dispersion and alignment of CNTs in polymeric composites.…”

“…A polymeric blend containing polydimethylsiloxane (PDMS) and poly(methyl methacrylate) (PMMA) was assembled following the procedure reported earlier by Yang et al and unmodified multiwall carbon nanotubes (MWCNTs) were added to the mixture. As described in earlier procedures, a solution prepared from 2.0365 g of PMMA (molecular weight 210 000), 2.02 mL of Sylgard‐184 PDMS with a molecular weight of ≈60 000, 0.2 mL of curing agent, 10 mL Dimethylformamide (DMF), 10 mL Tetrahydrofuran (THF), and 0.0083 g of MWCNT was mixed and placed under magnetic stirring for two weeks and then sonicated and electrospun with the following parameters: 8 kV, 5 cm distance, and 0.5 mL s −1 . It was spun onto a rotating drum to align the fibers.…”

“…In particular, dispersion and alignment of nanofillers are believed to unlock dynamical properties, key to highly innovative phenomena such as mechanical actuation and plasmonics . Previously, we have demonstrated correlation between processing and alignment through synchrotron and Raman spectroscopies as well as atomic force and helium ion microscopies in the context of structural, and smart (i.e., mechanically actuating) systems …”

Quantitative Evaluation of the Carbon Hybridization State by Near Edge X-ray Absorption Fine Structure Spectroscopy

“…The dependence of the intensity of the detected spectral features on the orientation of the final state orbital with respect to the electric field vector of the incident photon beam 58 also allows the surface molecular orientation of nanomaterials [59][60][61] and adsorbates 62 to be investigated.…”