Generation of Pretilt Angles in Nematic Liquid Crystal, 5CB, Media Aligned on Polyimide Films Prepared by Spin-Coating and LB Techniques: Effect of Rubbing

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Abstract
The pretilt angles generated in nematic liquid crystal (5CB) media that are disposed in sandwich type cells and oriented by using various orientation films are shown to depend both on the nature of the orientation films and the rubbing strengths in the following way: first, in a cell with alkyl branched polyimide (PI (1)) prepared by spin-coating, the obtained prettily angle 6P shows a giant peak reaching 51 degrees at the low rubbing strength (RS) region and then it decreases monotonically with the increase of the RS; second, with another alkyl branched PI (PI (2)), the obtained value of Q p is around 4 degrees for a wide range of the RS; third, with branchless spin-coated PI (PI (3)) that is featured by its high electrical polarization, the θ P increases monotonically with the RS from zero level and tends to saturate and level-off as θ P to be 4.5 degrees; fourth, with as stacked PI-Langmuir-Blodgett (LB) films using the same precursors as those used for above mentioned PI (1, 2, and 3), the θ P are always nil; finally, contrary to above results, by the application of rubbing on the PI-LB films with a medium RS, the obtained values of θ p are shown to take the following order; PI-LB (3) > PI-LB (2) > PI-LB (1). This order is the reverse compared with the data for the spin-coated and rubbed PI films.