(a) An SEM image of a photonic CNC film cross-section showing curves arising from CNC Bouligand arrangement. Reproduced with permission [57]. Copyright © 2017 ACS, Elsevier. (b) CD spectra of cellulose films produced from 1% by mass CNC suspensions with 0 (black solid), 0.1 (black dashed), 0.2 (dark grey solid), 0.3 (dark grey dashed), 0.4 (grey solid) and 0.5 mol cm−3 (grey dashed) NaCl, showing blue-shifting with increasing ionic strength. Reproduced with permission [58]. Copyright © 2010 ACS, Elsevier. Polarized optical microscopy and SEM images of (c,g) fast-dried, sodium-neutralized, (d,h) slow-dried, sodium-neutralized, (e,i) fast-dried, methyltriphenylphosphonium-neutralized, and (f,j) slow-dried, methyltriphenylphosphonium-neutralized CNC films. The measured pitch and standard deviations are observed to shift to lower values with slower drying (1000 ± 350 to 606 ± 151 nm) and greater surface hydrophobicity [1000 ± 350 to 619 ± 190 nm (fast) and 606 ± 151 to 504 ± 180 nm (slow)]. Reproduced with permission [57]. Copyright © 2017 ACS, Elsevier.