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题名	快速液晶材料的分子设计及校正器结构优化研究
作者	王启东
学位类别	博士
答辩日期	2015-05
授予单位	中国科学院大学
导师	宣丽
关键词	液晶波前校正器 响应速度 双折射率 旋转粘度 预倾角
其他题名	Molecular Design of Fast Response Liquid Crystals andResearch on the Optimization of Corrector Structures
学位专业	光学
中文摘要	液晶波前校正器是液晶自适应光学系统中的一个关键器件，其响应速度的快慢直接影响整个液晶自适应光学系统的校正效果。提高液晶波前校正器响应速度的根本办法就是改善液晶材料性能、优化校正器结构。根据液晶弹性体理论，并以固定位相调制量为约束条件推导可知，液晶波前校正器的响应速度正比于液晶材料双折射率∆n的平方，反比于液晶材料的旋转粘度 。因此，改善液晶波前校正器的材料性能就是要提高液晶材料的∆n并同时降低 。优化液晶波前校正器的器件结构需要研究三方面的内容：预倾角对响应速度的影响；最佳盒厚准确可靠的确定方法；平行模式液晶盒提高响应速度的机理以及其与反平行模式液晶盒响应速度的比较。 论文首先在经典理论的基础上，以谐振子模型分析了光与液晶分子的相互作用，清楚了液晶分子的∆n与液晶分子的电子极化率各向异性∆α密切相关；从量子力学的角度分析了液晶分子折射的物理机理，推导出了液晶分子的极化率与液晶分子半径的平方成正比，与最高占有轨道（HOMO）和最低未占有轨道（LUMO）的能量差成反比。结合价键理论得出了要想减小液晶分子HOMO与LUMO的能量差∆E，增大液晶的分子极化率并最终提高液晶∆n，必须延长液晶分子的共轭体系长度；研究了利用Vulks方程计算包括液晶在内的各向异性介质折射率的可行性，通过计算值和实验值的比较，发现利用该方程可以较为准确的计算不同种类不同结构液晶分子的∆n；研究了液晶分子中心基团尺寸与类型对∆n的影响，在此基础上，提出了稠环芳香烃类中心基团结构。通过分析轴向极性基团、侧向极性基团和柔性尾链对稠环芳香烃类液晶∆n的影响确定了四种高∆n的液晶分子结构。 提出了利用液晶分子动力学模拟来研究液晶分子旋转粘度以及相态的方法，详细给出了液晶分子旋转粘度计算的理论依据；通过模拟发现，一般高∆n液晶分子在313K附近处于近晶相，无法直接通过单体的模拟比较它们的旋转粘度大小，针对这一问题，首次提出了利用混合液晶分子动力学模拟来比较液晶分子旋转粘度的大小，并利用文献以及实验数据验证了这一方法的可行性和可靠性；通过比较四类高∆n液晶分子的双折射率、旋转粘度以及相态，发现稠环芳香烃类液晶理论上具有很高的∆n并同时具有相对较低的旋转粘度，其响应性能甚至能够超过苯-二苯乙炔类液晶的响应性能。粗略估计，如果将所设计的两种稠环芳香烃类液晶分子掺入到目前实验室所用的混合液晶中，响应速度能够提高约20%，因此稠环芳香烃类液晶在提高液晶波前校正器的响应速度方面具有非常大的潜力。 研究了固定位相调制量下预倾角对液晶波前校正器响应速度的影响，发现液晶波前校正器的响应速度随预倾角的减小而显著提高，因此为了提高液晶波前校正器的响应速度，必须尽可能的减小液晶盒基板表面的预倾角至1°左右；研究了数值计算法和单次光电测量法获得最佳盒厚的物理机理和理论依据，利用实验验证了两种方法确定最佳盒厚的可行性和准确性；研究了平行模式液晶盒提高液晶波前校正器响应速度的机理，在固定相位调制量下比较了平行模式液晶盒与反平行模式液晶盒的响应速度，发现如果平行模式液晶盒的分子流动明显加速了其转动，那么就可以选择平行模式液晶盒来加速液晶波前校正器的响应速度。 本论文采用理论与实验相结合的方法，并参考文献数据，系统的研究了通过改善液晶材料性能及优化校正器结构来提高液晶波前校正器响应速度的方法。相信本文所设计的新型液晶分子和器件结构必将进一步提高液晶波前校正器的响应速度，为提高整个液晶自适应光学系统的成像效果作出贡献。
英文摘要	Liquid crystal wavefront corrector (LCWFC) is a critical component of liquid crystal adaptive optical system, which response speed can directly affect the correction quality of liquid crystal adaptive optical system. The fundamental way to improve the response speed of LCWFC is to improve the performance of liquid crystal materials and optimize the structure of the corrector. Based on the elastic theory of liquid crystal, and to fix the phase modulation as the constraint conditions, the response speed of LCWFC is proportional to the square of birefringence ∆n of the liquid crystal material, inversely proportional to the liquid crystal material viscosity γ1. Therefore, the improvement of the material properties of LCWFC is to improve the ∆n of the liquid crystal material and at the same time reduce the γ1. The device structure optimization of LCWFC involves the following aspects: how pretilt angle can affect the response speed; how to achieve the optimal cell gap accurately and reliably; the mechanism to improve the response speed using the parallel mode and a comparison with the anti- parallel mode. Firstly, based on the classical theory, a harmonic oscillator model is used to analyze the interaction of light with the liquid crystal molecules, which clearly shows that the birefringence ∆n of the liquid crystal is closely related to the anisotropy of the electronic polarizability ∆α. The physical mechanism of the birefringence ∆n is achieved from a quantum mechanics viewpoint, it has been known that the anisotropy of the electronic polarizability ∆α is proportional to the square of the radius of liquid crystal molecule, inversely proportional to the energy difference of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Combining the valence bond theory, in order to reduce the energy difference between HOMO and LUMO, increase the molecular polarizability and ultimately improve the liquid crystal birefringence ∆n, the length of conjugated system must be extended. The feasibility of calculation of anisotropic mediums including liquid crystal using the Vulks equation has been studied by comparing the calculated value and experimental results. The effect of size and type of the central group on the birefringence has been studied, on the basis, we have designed a central group which consists of the polycyclic aromatic hydrocarbon. The molecular structures of four kinds of high ∆n were determined through the analysis of the influence of lateral axial polar groups, the polar group and the flexible tail chain on the ∆n of liquid crystal. A method to study the rotational viscosity and phase state of liquid crystal has been proposed based on the dynamic simulation of liquid crystal molecules and we have provided the detailed theoretical basis for the rotational viscosity calculation. According to the simulation, the liquid crystal molecules of high ∆n in the vicinity of 313K will be in the smectic phase, so we can’t compare their rotational viscosity directly through the simulation of monomer. To solve this problem, a method to compare the rotational viscosity of liquid crystals based on the molecular dynamics of mixtures has been established, which feasibility and accuracy have been verified using literature and experimental data. By comparing the birefringence, rotational viscosity and phase state of the liquid crystal molecules of high ∆n, we found that the liquid crystal containing the polycyclic aromatic hydrocarbon have a high ∆n and a relatively low rotational viscosity, which response performance can be even better than the liquid crystal containing the phenyl-acetylene benzene. It is predicted roughly that the incorporation of two designed molecules into the mixtures used in our laboratory will improve the response speed of 20%. So the liquid crystal with the polycyclic aromatic hydrocarbon has a great potential in improving the response speed of LCWFC. The effect of pretilt angle on the response speed of LCWFC has been discussed at a fixed phase modulation, and then the following conclusions are drawn: the response speed of LCWFC decreases with the increased pretilt angle, so in order to improve the response speed of LCWFC, the pretilt angle must be reduced as much as possible to about 1 degrees. The physical mechanism and theoretical basis for obtaining the optimal cell gap accurately from a numerical calculation and a single photoelectric measurement have been studied thoroughly and systematically, these methods have been analyzed theoretically and confirmed experimentally. Finally, the mechanism to improve the response speed using the parallel mode and a comparison with the anti- parallel mode have been discussed, and it is concluded that the parallel mode can be used to accelerate the response speed of LCWFC under the condition of accelerating molecular rotation obviously. A systematic study on the improvement of response speed of LCWFC has been performed combining theoretical analysis and experimental analysis, the reference data also included. We believe that the new liquid crystal molecules and the new structure of the device designed in this paper will further improve the response speed of LCWFC, which must greatly contribute to improve the imaging effect of the liquid crystal adaptive optical system.
公开日期	2015-12-24
内容类型	学位论文
源URL	[http://ir.ciomp.ac.cn/handle/181722/48911]
专题	长春光学精密机械与物理研究所_中科院长春光机所知识产出
推荐引用方式 GB/T 7714	王启东. 快速液晶材料的分子设计及校正器结构优化研究[D]. 中国科学院大学. 2015.

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