Accurate determination of liquid‐crystal tilt bias angles
Accurate determination of liquid‐crystal tilt bias angles
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DOI：
10.1063/1.323928
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发表时间：
1977-05
影响因子：
3.2
通讯作者：
T. Scheffer;J. Nehring
中科院分区：
文献类型：
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作者：
T. Scheffer;J. Nehring
本文详细分析了三种确定液晶与界面接触的倾斜偏角的方法。这些方法中的两种，晶体旋转和电容方法，具有严重的缺点，如应用范围有限，精度不足，有时需要的知识，必须通过单独的实验来确定的晶体材料常数。第三种更有用的方法是磁零位法，它可以直接确定倾斜偏角，只需一次测量，精度为0.1°，而不管角度的大小或液晶的性质。采用磁零点法研究了与倾斜蒸镀一层二氧化硅的玻璃基片接触的向列相的倾斜偏角。我们发现，倾斜偏角随蒸发角（两个角度测量样品平面），直到一个临界蒸发角？达到14°，于是指向矢重新定向到蒸发束的入射平面之外，并且呈现垂直于该平面的方向，具有0°倾斜偏置。我们还发现，不同的化合物的倾斜偏角相同的蒸发参数，并受温度和微量杂质。
A detailed analysis is given for three techniques used to determine the tilt bias angle of a nematic liquid crystal in contact with a boundary surface. Two of these methods, the crystal rotation and capacitive methods, have severe disadvantages, such as a restricted range of application, an insufficient accuracy, and sometimes require knowledge of nematic material constants which have to be determined by separate experiments. A third and more useful method, a magnetic null method, makes it possible to determine the tilt bias angle directly with only one measurement to an accuracy of 0.1°, regardless of the size of the angle or the nature of the nematic liquid crystal. Using the magnetic null method we have investigated the tilt bias angles of nematics in contact with glass substrates onto which a coating of SiO had been obliquely evaporated. We find that the tilt bias angle decreases with increasing evaporation angle (both angles measured from sample plane) until a critical evaporation angle of ?14° is reached, whereupon the director reorients out of the plane of incidence of the evaporation beam and assumes a direction normal to this plane with a 0° tilt bias. We also find that the tilt bias angle varies from compound to compound for the same evaporation parameters and is influenced by temperature and trace impurities.