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The chemical mapping capability of PiFM is demonstrated in an asphalt sample containing multiple related components.
Note in the accompanying spectra that the signal strength for maltene is lower than asphaltene except at ~1501 cm−1 (shown in dotted circles on both PiFM and FTIR spectra).
This small difference is easy to overlook until rendered in a PiFM image. The PiFM image acquired at 1501 cm−1 clearly highlights the continuous maltene phase, in sharp contrast to the PiFM image at 1469cm−1 that identifies the islands as asphaltene.
Asphaltene has a higher molecular weight and contains a lot of aromatic structure. Maltene has a lower molecular weight, lower viscosity (more oily), and has more saturated (less aromatic) structure than asphaltene.
“Bitumen can be defined as a dark brown to black cement-like material, whose compounds can be classified into two generic groups, maltenes and asphaltenes. Asphaltenes are the black-colored fraction, insoluble in n-heptane, and having the highest polarity and molecular weight, whereas maltenes, also soluble in this solvent, are composed of saturated and aromatic compounds, and resins.” -Excerpt from McNally, Tony, (Nanotechnologist), (editor of compilation.) Polymer modified bitumen: properties and characterisation. Woodhead Publishing, Oxford, 2011.
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