With the strong current trend in nanotechnology to focus on sustainably produced high-value nanomaterials, cellulose nanocrystals (CNC) are emerging as a particularly interesting candidate. CNCs are stiff rods of crystalline cellulose with some 5 nm diameter and lengths ranging from hundreds of nanometers to a few microns. They are sustainably produced from bioresources with large-scale production capacity. They are attractive for new functional materials development due to their mechanical, optical and thermal properties and, most importantly, because aqueous colloidal CNC suspensions self-assemble into helically modulated cholesteric liquid crystal phases. Solid films with internal periodicity in the range of a few hundred nanometers can be made by drying the suspension, effectively producing a photonic crystal paper.While the rich potential of CNC is easy to see, the current understanding of the physics of CNC suspensions is unsatisfactory, in particular regarding the equilibrium phase diagram and the competition between liquid crystal formation and jamming into an arrested non-equilibrium state. This competition not only poses an engineering challenge but is a fascinating topic of current basic research in statistical mechanics.We, one experimental and one theoretical soft matter group, propose to join forces in this multidisciplinary project and tackle the technological challenge as well as the basic physics question. We will study the balance between liquid crystalline ordering and jamming in experiments and computer simulations. The experiments will use optical microscopy on samples prepared with varying CNC concentration and tuned ionic strength, monitoring the samples while the water is evaporated under carefully controlled conditions. The photonic properties will be studied by combining optical microscopy and spectrophotometric investigations. The Monte Carlo and Molecular Dynamics simulations will establish the phase diagram and characterize the jamming transition of helical Yukawa rods, aiming at a theoretical description of the interplay between the formation of helically modulated long-range orientational order and the slow, glass-like dynamics of the jammed state.The expected output has value both in terms of fundamental physics understanding and in clarifying mysteries that are of key practical importance for realizing the high-value photonic materials and biomimetic composites that are currently the main applied targets of CNC research.