Colourful patterns in cellulose-based liquid crystals

Cellulose-based thermotropic and lyotropic liquid crystals can be obtained from macromolecules or colloidal particles, such as cellulose nanocrystals. Thermotropic liquid crystals are produced by the effect of temperature, while lyotropic liquid crystals occur in solution for a given range of concentration, pressure, and temperature. Cellulose liquid crystals can form chiral nematic phases characterized by Bragg-type reflections of circularly polarized light. This characteristic is related to a helical structure formed by pseudo nematic layers twisted around an optical axis. The helical structure is characterized by the values of pitch and helicity. The later can be right- (R) or left- (L) handed. Cellulose liquid crystals are well described in literature. They are a source of materials for many applications, including the production of photonic chiral materials. Although many questions remain unanswered such as the origin of helicity of cellulosic chiral structures and those related to out-ofequilibrium systems. In this paper, we are focused at the out-of-equilibrium systems obtained from lyotropic cellulose-based liquid crystals. The development of colorful patterns involving the pitch variation in space and time of self-organized cellulose cholesteric structures is revised.