Fundamental Investigations of Liquid Crystal Devices

这个项目的主要目标是研究液体喷射的外部和自我刺激产生液滴的过程。对飞溅和液滴破碎的基本了解具有广泛的工业应用，从降雨、作物喷雾和喷漆到喷墨打印。一个特别令人感兴趣的应用是喷墨打印，这是一种成熟的文档打印技术，可以扩展到活性物质和液晶的沉积。牛津大学流体动力学实验室已经成功地建立了内部LC喷墨系统，并用于沉积可调微透镜。然而，这对液滴形成和撞击过程的基本动力学，特别是撞击后微秒内导向器的松弛，提供了很少的洞察力。初步调查表明，这种情况发生的时间尺度与液滴形成的时间尺度相似。因此，有可能在撞击后的微秒内冻结导向器场，从而允许创建新的LC结构。实验室中的高速成像装置将与计算机模拟(格子-玻尔兹曼)相结合，以提供对这一过程的更全面的了解。为了观察导向器，将建立一个基于时间分辨的透射式和反射式偏振成像系统，该系统将使用高速彩色摄像机，并通过倾斜的下降路径实现。这些观测将与液滴形状的阴影测量同时进行。CFD模拟将被用来支持新的喷射和破碎模拟技术的开发，以验证实验结果，并推动在喷射破碎主题内进行更广泛的探索。从长远来看，可能的沉积材料和衬底的范围将扩大到包括活性向列相和软物质。主要的挑战包括抑制不受欢迎的“卫星”水滴，以及开发替代的水滴产生机制(目前使用的方法都是压电式的)--如果克服这些问题，可能会为扩大水滴的实际使用范围和时间范围开辟道路。该项目的最新进展是我们模拟能力的新扩展。一个复杂的新型三元格子Boltzmann模拟系统将与液晶动力学的有限差分解算器结合使用，以产生一个新的模拟系统，它可以模拟一系列问题，包括但不限于液滴在湿层衬底上的滴落、通过蒸发产生的液体透镜等。从长远来看，这样的系统将被用来启发和测试LC设备中的新概念，目的是创造超出当前LC显示技术主流的新技术。这属于EPSRC连续介质力学和复杂流体和流变学研究领域。该项目是牛津工程科学的流体动力学实验室和牛津大学理论物理系的软和生物物质小组合作的项目。

The broad objective of this project is to study the generation of droplets by external and self-stimulation of liquid jets. A fundamental understanding of splashing and drop breakup has a wide range of industrial applications, from rainfall, crop spraying and spray coating to inkjet printing. One particular application of interest is inkjet printing - a mature technology for document printing that offers promising expansions into the deposition of active matter and LCs (Liquid Crystals).In-house LC inkjet systems have successfully been built in the Fluid Dynamics Laboratory in Oxford and used to deposit tunable microlenses. However, this provides little insight into the underlying dynamics of the drop formation and impact processes, in particular the relaxation of the director during the microseconds after impact. Preliminary investigations suggest that the timescale over which this occurs is similar to that of the droplet formation. It may therefore be possible to 'freeze' the director field in the microseconds after impact, allowing for the creation of novel LC structures. High-speed imaging rigs in the lab will be combined with computer simulations (Lattice-Boltzmann) to provide a more comprehensive understanding of this process.To make observations of the director, a time-resolved transmission- and reflection-based polarization imaging system will be built with a high-speed colour camera, enabled by an angled dropping path. These observations will be made concurrently with shadowgraphy measurements of the droplet's shape. CFD simulations will be used to support the development of new jetting and breakup simulation techniques, to verify experimental results and prompt wider explorations within the topic of jet breakup.In the long term, the range of possible deposition materials and substrates will be expanded to include active nematics and soft matter. Primary challenges include the suppression of undesirable 'satellite' drops, and the development of alternative drop generation mechanisms (the current methods in use all being piezoelectric) - if overcome these may open avenues to the expansion of the range of length and time-scales over which dropping is practicable.The most recent developments in the project are new expansions of our simulation capacity. A sophisticated new ternary Lattice Boltzmann simulation system will be used in combination with a finite-difference solver for the liquid crystal dynamics to produce a new simulation system that can model a huge range of problems, including but not limited to the dropsition of LC droplets on wet-layer substrates, liguid lens generation by evaporation and more. In the long term, such a system will be used to inspire and test novel concepts in LC devices, with the aim of creating new technologies that go beyond the current LC mainstay of display technology.This falls within the EPSRC Continuum Mechanics and Complex Fluids and Rheology research area. The project is a collaboration between the Fluid Dynamics Laboratory in Oxford Engineering Science and the Soft and Biological Matter group in the Department of Theoretical Physics, University of Oxford.