A nanoscale chemical characterization of wood and cellulose-based materials is of crucial importance to improve our understanding about how these materials are constructed and how we can modify them and improve their performance. Quite recently such studies have become possible with the technique Infrared nanospectroscopy, a combination of atomic force microscopy (AFM) and infrared (IR) spectroscopy, enabling IR spectra and IR images to be acquired with a lateral resolution of around 20 nm, hence significantly better than the diffraction limit. [1]
In these studies, Infrared nanospectroscopy has been used to examine cellulose nanofibrils (CNFs) of tunicate and wood, as well as cellulose nanocrystals (CNCs) from cotton by acquiring IR spectra along individual CNFs/CNCs, in order to reveal their local morphology on the nanoscale. [2] By comparing the nanoscale spectra of the individual fibrils with reference IR spectra of films of crystalline and non-crystalline cellulose, the local crystallinity could be determined.
Wood cell walls are a few micrometers wide and consist of several layers such as the middle lamella, the primary, and the secondary wall, some of them being only around a hundred nm wide. These layers have different compositions of the wood constituents cellulose, lignin, hemicellulose, and pectin, and here Infrared nanospectroscopy has been used to chemically study their abundance in the different layers. In addition to nanoscale IR spectra, the cell walls have been characterized by AFM.