Collaborative Research: Understanding Cholesteric Pitch in Nanocylinder Films

CBET 1436637/1437073液态晶体是既表现出结晶有序性又表现出液体流动性的物质相。该项目将研究能够形成液晶的纳米柱状分散体的性质。被研究的特定液晶被称为胆甾体(手性)，因为纳米柱排列在一个优选的方向上，但优选的方向本身绕着一个轴旋转。由于这种结构，胆甾型液晶可能具有不寻常的光学性质。当材料被加工成薄膜时，其独特的结构和光学性能保持不变，这使得这种材料特别适用于液晶显示器、装饰涂层和特种油墨等应用。本项目将研究纳米柱状分散体的流变性，并分析流体在加工成薄膜时如何改变材料的微观结构特征和光学性质。这些结果将有助于科学家和工程师设计和加工胆甾型液晶薄膜，使其具有可控的光学性质。实验和模拟相结合的方法将用于了解分散性质和流动对分散、流变性和形态性质的影响。这将导致分散性、流变性和微观结构作为组成和剪切速率的函数的参数空间图。将研究两种能够形成溶致胆甾型液晶的模型体系：磺化纤维素纳米晶的水分散体和双链DNA和单壁碳纳米管的水分散体。对于这两个系统，将使用介观多域模拟技术和物理实验相结合的方法来研究以下特征：1)振荡流变学所探索的微观结构(织构)作为介元浓度的函数；2)稳态剪切启动过程中的瞬变；3)稳态剪切流变行为，特别是在低剪切下；4)静止织构和停流后织构的发展；以及5)固化薄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.