Collaborative Research: Understanding Cholesteric Pitch in Nanocylinder Films

液晶是一种既具有晶体秩序又具有液体流动性的物质相。该项目将研究可以形成液晶的纳米圆柱体分散体的特性。所研究的特殊液晶被称为胆甾（手性）液晶，因为纳米柱排列在一个优选方向，但优选方向本身围绕一个轴旋转。由于这种结构，胆甾液晶可以具有不同寻常的光学性质。当材料被加工成薄膜时，不寻常的结构和光学特性被保持，这使得材料在液晶显示器、装饰涂料和特种油墨等应用中特别有趣。本项目将研究纳米圆柱体分散体的流变特性，并分析在加工成薄膜时流动如何改变材料的微观结构特征和光学特性。研究结果将帮助科学家和工程师设计和加工胆甾液晶，使其成为具有可控光学特性的薄膜。实验和建模的结合将用于了解分散特性和流动对分散流变和形态特性的影响。这将产生作为组分和剪切速率函数的分散流变性和微观结构的参数空间图。我们将研究两种能够形成溶性胆固醇甾体液晶的模型系统：磺化纤维素纳米晶体的水分散体和双链DNA和单壁碳纳米管的水分散体。对于这两个系统，将结合介观多域建模技术和物理实验来研究以下特征：1)振荡流变学检测的微观结构（织构）作为中质浓度的函数，2)稳态剪切启动时的瞬态，3)稳态剪切流变行为，特别是在低剪切时，4)静止织构和流动停止后的织构发展，5)固化膜的织构和光学性质。

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.