Detecting carbon in carbon: Exploiting differential charging to obtain information on the chemical identity and spatial location of carbon nanotube aggregates in composites by imaging X-ray photoelectron spectroscopy

Abstract

To better assess risks associated with nano-enabled products including multiwalled carbon nanotubes (MWCNT) within polymer matrices, it is important to understand how MWCNT are dispersed throughout the composite. The current study presents a method which employs imaging X-ray photoelectron spectroscopy (XPS) to chemically detect spatially segregated MWCNT rich regions at an epoxy composites surface by exploiting differential charging. MWCNT do not charge due to high conductivity and have previously been shown to energetically separate from their insulating surroundings when characterized by XPS. XPS in imaging mode revealed that these conductive regions were spatially separated due to micrometer-scale MWCNT aggregation and poor dispersion during the formation of the composite. Three MWCNT concentrations were studied; (1, 4 and 5) % by mass MWCNT within an epoxy matrix. Images acquired in periodic energy intervals were processed using custom algorithms designed to efficiently extract spectra from regions of interest. As a result, chemical and electrical information on aggregate and non-aggregate portions of the composite was extracted. Raman imaging and scanning electron microscopy were employed as orthogonal techniques for validating this XPS-based methodology. Results demonstrate that XPS imaging of differentially charging MWCNT composite samples is an effective means for assessing dispersion quality.

Thin films deposition versus nanoparticles formation: How can the desired polymer coating be obtained?

“…In the case of a thin film on a conductive substrate (e.g., silicon wafer), this positive charge is compensated by electrons from the conductive substrate but if the coating is thicker or rougher (for instance due to the presence of polymer particles in the coating), the compensation can no longer occur, leading to a peak shift. [23,24] These remarks are consistent with the fact that Figure 2b corresponds to the spectrum of a maleic anhydride plasma polymer coating made of both a polymer thin film and polymer nanoparticles. Besides, ATR FTIR analyses have also been carried out for both types of coating morphologies and they have revealed chemical fingerprints of maleic anhydride plasma polymer for both cases (Figure S2).…”

A new holder/container with a porous cover for atomic layer deposition on particles, with transport analysis and detailed characterization of the resulting materials

“…While by no means a perfect solution, the C 1 s peak position is a commonly used reference in XPS. For the samples in this study, this referencing produces consistent results 50 . XPS spectra from bare silicon wafers, alumina deposited on silicon, zinc oxide, and zirconia have previously been reported in the scientific literature 51–54 …”

“…The performance of the holder was demonstrated with 5-μm zirconia particles that were coated with alumina from trimethylaluminum (TMA) and water, and with zinc oxide from diethylzinc (DEZ) and water. Deposition on different amounts of particles was investigated (50,100,200, and 500 mg). Parasitic chemical vapor deposition (CVD) appeared to be present when a greater number of particles or meshes were used.…”

Hypochlorite degrades 2D graphene oxide sheets faster than 1D oxidised carbon nanotubes and nanohorns

“…S1) than suggested by TGA. This may be because XPS is a surface technique that only allows a detailed regional surface analysis (analysis depth ≈ 10 nm), 31 as opposed to TGA which considers the entire sample structure allowing a more global analysis. 32 This is especially important when analysing OxMWNT and OxNH dahlia like structures, which have internal and external structural components, compared to 2D GO which does not.…”