Hydration-driven structural evolution in cross-linked cellulose-based xerogels probed by 2DCOS and PCMW2D correlation spectroscopy applied on SANS data

In this work, small angle neutron scattering (SANS) data of branched polyethyleneimine (bPEI)/TEMPO-oxidized and ultrasonicated cellulose nanofiber (TOUS-CNF) xerogels, namely cellulose nano-sponges (CNSs), at different hydration level (h) and cross-linker amount, were analyzed through a combined approach involving generalized (2DCOS) and perturbation-correlation moving window (PCMW2D) two-dimensional correlation spectroscopy. The aim was to get novel insights into the sequence of structural changes experienced by the xerogel moieties upon hydration, based on the assessment of the cross-correlations existing at different length scales retrieved by the synchronous (SCMs) and asynchronous (ACMs) 2DCOS and PCMW2D correlation maps calculated upon variation in the chosen perturbation variable. It is worth noting that the application of 2DCOS and PCMW2D on SANS data enabled the identification of structural transitions that are not readily apparent from conventional SANS analysis, highlighting the sensitivity of this method in detecting structural dynamics as well as any minor changes in the polymer arrangement at both low and high spatial scales.