Characterization of Nanomaterials by Vapor Sorption Techniques

In recent years, the study and applications of nanomaterials have gained tremendous interest, due to their electronic, thermal, mechanical, optical, and magnetic properties, creating potential applications in a wide range of fields, including electronics, energy conversion / storage, sensing, and drug delivery. These materials are energetically inhomogeneous, exhibiting various surface sites, such as structural defects or specific functional groups

Vapor sorption techniques play a vital role in the characterization of nanomaterials and in particular IGC SEA has been proven as a powerful and sensitive technique for assessing the surface energy and surface chemistry of carbon-based nanomaterials. Figure 1 shows the dispersive surface energy distributions for as received, annealed and thermally oxidized carbon nanotube samples.

Figure 1. Dispersive surface energy profiles

The received sample shows γ_S^D values between ~ 87 and ~107 mJ/m². Following thermal annealing the surface shows much smaller variations in γ_S^D (~87 to ~95 mJ/m²), implying a more homogeneous surface. Though γ_S^D values of as-received and annealed samples differ at lower surface coverages (less than 6%), their γ_S^D overlap at higher surface coverages. This highlights the importance of measuring surface energetic heterogeneity profile for real solids. The oxidised sample shows a much wider range of γ_S^D values, varying from ~102 to ~150 mJ/m². This may be due to the introduction of additional surface functional groups with high γ_S^D and the creation of structural defects (such as perforations and graphene edges). Using such energy mapping techniques, IGC SEA can reveal specific changes in surface character, e.g. surface polarity or acid-base surface chemistry, that are not readily accessed by other conventional techniques, but which are highly relevant to both processing and application of nanomaterials.

The in-situ monitoring of vapour interactions with nanomaterials may also be investigated by a unique combination of Dynamic gravimetric Vapor Sorption (DVS) with a fiber optic Raman probe. Raman spectroscopy is an integral part of carbon nanomaterial research because it plays a vital role in the characterization of these materials and can be used to evaluate the number of layers, type and relative quantity of defects, mechanical strain, and functionalization and doping in addition to several other parameters that are specific to each carbon nanomaterial[2].

References[1] Schnorr, J.M. and Swager, T.M. Emerging applications of carbon nanotubes. Chem. Mater. 2011, 23(3), 646-657.[2] Malard, L.M.; Pimenta, M.A. et al. Raman spectroscopy in graphene. Physics Reports—Review Section of Physics Letters  2009, 473, 51–87.

About the author:
Dr Majid Naderi is the Laboratory Manager at Surface Measurement Systems and his academic degrees include MSc. in Petrochemicals and Ph.D. in Physical Chemistry.