Bouligand Multilayers—Artificially Constructed Cellulose Nanocrystals Chiral Films

Natural photonic crystals, such as cellulose nanocrystals, have the ability to self-assemble into complex hierarchical structures, however, because of the homochirality in nature they can only assemble into left-handed chiral structures. Here, we will demonstrate bottom-up approach to assemble cellulose nanocrystals thin films of both handednesses. First, we assembled linearly oriented CNC monolayer via shear-induced alignment. Then, artificial chiral Bouligand nanostructures were constructed via Layer-by-Layer (LbL) deposition technique by depositing each next layer in clockwise and counter-clockwise fashion rotating the substrate at a fixed angle. The chiroptical properties measurements of the obtained thin films resulted in mirror-imaged circular dichroism (CD) spectra, indicating successful construction of both left- and right-handed CNC films. Those chiroptical properties and films’ anisotropy will be controlled by changing the rotation angle and the number of deposited layers, i.e., film’s thickness. Our fabrication strategy has several advantages. First, doctor blade deposition technique allows to produce large-area films. Second, LbL deposition guarantees precise control of the rotation angle and direction. Atomic force microscopy will confirm the alignment of the monolayers deposited, as well as their thickness in conjunction with ellipsometry. CD and UV-vis studies will reveal chiral optical activity of the deposited films. Lastly, effectiveness of artificially obtained chiral photonic CNC films will be confirmed by the g-factor, dimensionless factor characterizing the efficiency of the light-passing-through-the-film polarization and will be presented. Such control of the CD response with respect to the peak sign, position and intensity is unique for CNC films.