Characterization of multi-walled carbon nanotube dispersion in resorcinol–formaldehyde aerogels

• The homogeneity of MWCNT/RF aerogels is evaluated from mm to nm scale.
• At low concentration (<0.26 v%), nanotube bundles are completely exfoliated.
• Above 0.26 v%, aggregates of MWCNTs with diameters up to 50 μm are observed.
• Thermal conductivity of the composites is compared to the Effective Medium Theory.
• The fraction of separated MWCNT was evaluated from the observed deviation.

Multi-walled carbon nanotube (MWCNT)/resorcinol–formaldehyde (RF) composite gels were prepared by sol–gel polymerization of RF monomers in a suspension of carbon nanotubes in water, followed by CO2 supercritical drying. X-ray microtomography showed that the suspensions of MWCNTs were stable and that the distribution of nanotubes throughout the RF matrix was uniform. The level of MWCNT dispersion in the composites was evaluated by microscopic methods (optical microscopy, SEM and TEM). Micrographs showed that, at low MWCNT concentration (<0.26 v%), the nanotube bundles were completely exfoliated, leading to a homogeneous material at the nanometer scale. On the contrary, at higher concentrations, aggregates of MWCNTs with diameters up to 50 μm were observed. N2 sorption analysis showed that the carbon nanotube aggregation may result in a decrease of BET surface area of the composites. Thermal conductivity of the nanocomposites was measured by TPS hot disk method and the data were consistent with effective medium theory (EMT). At high MWCNT loadings, it was possible to estimate the volume fraction of separated and aggregated carbon nanotubes based on the deviation of the experimental conductivity data from EMT predictions.

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