Macroscopic mapping of the linear in-plane anisotropy of nanocellulosic thin films by Mueller matrix polarimetry

The present work focuses on the characterization of the macroscopic optical anisotropy of cellulosenano- composite multilayer thin films prepared by grazing incidence spraying. The polarizationproperties of such films composed of in-plane aligned cellulose nanofibrils embedded in apolyelectrolyte multilayer are investigated by Mueller matrix polarimetry (MMP). Linearbirefringence is the predominant polarization property resulting from the unidirectionalorganization of the cellulose nanofibrils, thus, the differential decomposition of the Mueller matrixmeasured on the films allows the determination of their actual structural birefringence, 〈Δn〉 =0.032. Moreover, modeling the sample as an effective medium provides a parametrized expressionthat describes its linear birefringence as a function of the optical constants of the components, thevolume fraction of nanofibrils, the distribution of orientation, and the film thickness. Therefore,MMP provides a fast, simple, and non- destructive method to characterize both the structuralcharacteristics and the optical birefringence/dichroism of the films over large areas, which is of greatinterest for various optoelectronic applications.