The 32 d sample was further analysed using 2D 13 C heteronuclear single-quantum correlation (HSQC) spectroscopy. The sample was analysed initially in the [P4444][OAc]:DMSO-d6 electrolyte, to further confirm the bulk regioselectivity of acetylation (Figure ). The sample was also suspended in DMSO-d6, where only surface chains can be exfoliated into solution (Figure ), further allowing determination of regioselectivity. The nanocrystalline nature was also confirmed to be preserved by high-resolution AFM after casting from DMSO (Figure , d) -importantly, the acetylation resulted in partial recovery of the elementary nanocrystals (Figure ) from the typically observed clusters (Figure ). While the cross-sections of the pristine CNCs highlight a clean baseline, with features below 0.3 nm (Figure ), features larger than 2 nm that are not associated with CNC morphology are observed after acetylation (Figure ). The larger features on the baseline indicate exfoliation of the functionalized cellulose chains, subsequently aggregated onto the substrate. The HSQC in When the HSQC of the CNCs dispersed in DMSO-d6 (where only CNC surface chains are in solution -only solvated chains are 'visible' using solution-state NMR) was analysed, a similar ratio of geminal-CH2 6 (6-OAc) and unmodified geminal-CH2 6 correlations were apparent, from the correlation peak volumes. This ratio would be consistent with the cellulose Ib crystalline structure , where rotation of adjacent AGUs in the crystal lattice results in every alternate polymer AGU 6-OH surface-facing. This further supports the regioselective surface coverage model. As shown in Figure , at bulk DS levels close to the complete C6-OH substitution, the regioselectivity starts to decrease. A small amount of 2-CH (2-OAc), consistent with the diffusion-edited 1 H results, is also visible. While it is expected that primary alcohols should react faster, such high regioselectivity was quite unexpected, and has been so far only reported in the case of aqueous-based solid and liquid acylations using N-acylimidazoles . In comparison to acetylation in the dissolved state , selectivity is clearly significantly improved.