Collaborative Research: Understanding Cholesteric Pitch in Nanocylinder Films

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CBET 1436637/1437073Liquid crystals are material phases that exhibit both crystalline order and the fluidity of a liquid. This project will investigate the properties of nanocylinder dispersions that can form liquid crystals. The particular liquid crystals being investigated are termed cholesteric (chiral) because the nanocylinders align in a preferred direction, but the preferred direction itself rotates about an axis. As a result of this structure, cholesteric liquid crystals can have unusual optical properties. When the materials are processed into thin films, the unusual structure and optical properties are maintained, which makes the materials especially interesting for applications such as liquid crystal displays, decorative coatings, and specialty inks. This project will investigate the rheological properties of nanocylinder dispersions and analyze how flow changes the microstructural characteristics and optical properties of the materials when processed into thin films. The results will help scientists and engineers to design and process cholesteric liquid crystals into films with controlled optical properties.A combination of experiments and modeling will be used to understand the effects of dispersion properties and flow on dispersion rheological and morphological properties. This will result in parameter space maps for the dispersion rheology and microstructure as a function of composition and shear rate. Two model systems capable of forming lyotropic cholesteric liquid crystals will be investigated: aqueous dispersions of sulfonated cellulose nanocrystals and aqueous dispersions of double stranded DNA and single-walled carbon nanotubes. For both systems, a combination of mesoscopic polydomain modeling techniques and physical experiments will be used to investigate the following features: 1) the microstructure (texture) as a function of mesogen concentration as probed by oscillatory rheology, 2) transients during the start-up of steady shear, 3) the steady shear rheological behavior, particularly at low shear, 4) texture at rest and texture development after flow cessation, and 5) texture and optical properties of solidified films.