Cellulose nanocrystals are an excellent example of biosourced nanomaterials with a unique combination of mechanical and optical properties, and as recently shown, with unique polarization properties. These nanorods form a stable suspension in aqueous solution and arrange into a cholesteric liquid crystalline phase above a critical concentration. Such behavior can be preserved in dry films, leading to the strong reflection of specific wavelength in the visible with a left circular polarization. Nevertheless, the films produced so far usually display a polydomain structure, whereby the orientation of the helix h is not controlled and leads to a pixelized and polychromatic aspect. Although chemical and physical methods have both been used to control their optical response, the use of external fields, e.g., electric and magnetic, has been limited to only a few examples. Recently, our two groups (Vignolini and Heux) have demonstrated the possibility of using magnetic and electric fields, respectively, to control the optical response of photonic cellulose-based structures. In this talk, I will discuss how electric and magnetic fields can be synergetically employed/engineered to control the optical properties of CNC suspensions in order to generate a uniform orientation of cholesteric domains along the vertical direction at the macroscopic scale. Similarly, by controlling the angle of the applied field, the generation of additional spectral characteristics in the suspensions are investigated.

Magnetic and electric field alignment of cellulose nanocrystal suspensions

2019 Spring National Meeting

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