Linear Birefringent Films of Cellulose Nanocrystals Produced by Dip-Coating

Transparent films of cellulose nanocrystals (CNC) are prepared by dip-coating on glass substrates from aqueous suspensions of hydrolyzed filter paper. Dragging forces acting during films deposition promote a preferential alignment of the rod-shaped CNC. Films that are 2.8 and 6.0 mu m in thickness show retardance effects, as evidenced by placing them between a linearly polarized light source and a linear polarizer sheet in the extinction configuration. Transmission Mueller matrix spectroscopic ellipsometry measurements at normal incidence as a function of sample rotation were used to characterize polarization properties. A differential decomposition of the Mueller matrix reveals linear birefringence as the unique polarization parameter. These results show a promising way for obtaining CNC birefringent films by a simple and controllable method.Funding Agencies|Concayt-Mexico [454210, 463797]; Conacyt [2018-000007-01EXTV-00169]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [2009-000971]; LIDTRA (Conacyt) [N-295261, LN-254119]; Knut and Alice Wallenberg foundation; Swedish Research Council; Carl Tryggers foundation