Variable liquid crystal pretilt angles of any value from 0 to 90° can be obtained by using a nanostructured alignment layer. This layer is robust and reliable. The pretilt angles obtained are stable against high storage and operating temperatures, and have strong anchoring energies.

The pi-cell is studied as a function of its pretilt angle. It is shown experimentally and theoretically that the critical holding voltage decreases as the pretilt angle increases. At high pretilt angles, the critical holding voltage becomes zero and the bend cell becomes stable. The measured total response time of the pi-cell decreases with the pretilt angle as well. There is almost a factor of 2 difference between the total response time of conventional pi-cell and the no-bias bend cell.The pi-cell, also known as the optically compensated bend ͑OCB͒ mode liquid crystal display ͑LCD͒, is capable of fast total response times of less than 1 ms. 1-6 The pi-cell operates between the bend deformation ͑B state͒ at low voltage and the homeotropic state at high voltage. Its response time can be very fast since there is no backflow involved in its' switching.However, the normal OCB cell is actually stable in the splay state ͑S state͒ because the pretilt angle is not high enough. Thus, an OCB display has to be converted ͑primed͒ to the B state first by applying a critical conversion voltage; then a holding voltage is needed to maintain the LCD in the B state. The transformation of a splay cell to the bend state is nontrivial. Since the S state and the B state are topologically inequivalent, nucleation has to be initiated. Many techniques have been proposed to prime the OCB cell into the B state. 7,8 For a large multiplexed display, it is quite difficult to convert the interpixel areas to the B state since there is no voltage across the liquid crystal ͑LC͒ cell in those regions. As a result, the optical performance of the LCD is degraded.Obviously, the critical voltage needed to convert the S state to the B state depends on the pretilt angle of the LC cell. However, no systematic experimental study of this critical voltage has been reported. In this letter, we present theoretical as well as experimental results on the critical voltage needed to transform the S cell to the B cell, as a function of the pretilt angle. This study is made possible by our ability to make LC cells with arbitrary pretilt angles.The fabrication of LC cells with any value of pretilt angle has been discussed previously. It is based on a new nanostructured alignment layer. 9,10 This alignment layer consists of a random distribution of nanoscale domains of homogeneous and vertical alignment materials that impart either vertical or horizontal alignment to the LC molecules. Due to elastic energy minimization, the LC cell will acquire a uniform tilt angle at a short distance above the alignment layer. It is noted that the process is very controllable and repeatable, once the fabrication procedures are fixed. 10 We made a series of LC cells with various pretilt angles and measured their critical voltages. The thickness of the liquid crystal layer was 5 m. The LC material used in the experiment was MDA-01-4679 from Merck with birefringence ⌬n = 0.2001, the elastic constants are K 11 = 14.5 pN and K 33 = 15.3 pN. The critical voltage is measured by observing ...

Abstract-We demonstrate a liquid crystal alignment layer with controllable polar and azimuthal anchoring energies. This alignment layer is based on a nanostructured surface formed by mixing a conventional polyimide and a nonaligning polymer. By using this variable anchoring alignment layer, large cell gap bistable twisted nematic LCD requiring asymmetric anchoring can be fabricated.