Effect of high pretilt angle for anchoring strength in nematic liquid crystal on rubbed polyimide surface containing trifluoromethyl moieties

The effects of high pretilt angle are investigated on the polar anchoring energy of the nematic liquid crystal (NLC), 5CB, on rubbed polyimide (PI) films containing trifluoromethyl moieties. The pretilt angle of 5CB rapidly increases up to about 45°with the rubbing strength (RS). Also, the polar anchoring energy of 5CB initially increases with the RS for weak rubbing and then decreases. From these results, we determined the relationship between the pretilt angle and the anchoring energy on rubbed PI films. We suggest that the polar anchoring energy of 5CB with a high pretilt angle is very small because of the combination of the microsurface excluded volume effect and the van der Waals interaction between the LC molecules and the substrate surface on weakly rubbed PI films containing trifluoromethyl moeities.