Epilogue

Abstract

We started the work on liquid crystal surfaces and interfaces with a question “Why do certain surfaces align liquid crystals and others not?”. Now, at the end of this book we can give the following answer: “We do understand and see what are the mechanisms that are responsible for liquid crystal alignment. Although these may differ from one surface to another, there are clearly common features”. On polymer surfaces, the predominant alignment mechanism is due to polymer chain and side group alignment in the top layer of the polymer, together with surface corrugations. By the combined output of the various methods presented, we do now understand, why rubbed polyimide shows alignment parallel to the rubbing direction, why rubbed polystirene aligns perpendicular to the rubbing direction, and what is the origin of the pretilt angle. We know, that only a statistically significant number of bonds with preferred orientation in the top layer of a polymer is enough to induce macroscopic liquid crystal alignment. There is no need for regions of crystalline or quasi-crystalline order, which is most clearly demonstrated in amorphous carbon alignment layers, formed by random bombardment of a polymer surface.