In liquid crystals homogeneous alignment, sometimes called planar alignment, is the state of alignment where molecules align in parallel to a substrate. The opposite method is homeotropic alignment.
For planar alignment - polyimides can be used. One of the popular ones is PI-2555.
The surface has to be rubbed by paper or by a velvet or similar cloth in order to make the alignment axis parallel to the rubbing. However the exact mechanism of this alignment is not entirely clear.
References
Jones, Lesley Parry (2012), Chen, Janglin; Cranton, Wayne; Fihn, Mark (eds.), "Alignment Properties of Liquid Crystals", Handbook of Visual Display Technology, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 1390–92, doi:10.1007/978-3-540-79567-4_86, ISBN 978-3-540-79566-7, retrieved 2025-01-08 978-3-540-79566-7 ↩
Jones, Lesley Parry (2012), Chen, Janglin; Cranton, Wayne; Fihn, Mark (eds.), "Alignment Properties of Liquid Crystals", Handbook of Visual Display Technology, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 1390–92, doi:10.1007/978-3-540-79567-4_86, ISBN 978-3-540-79566-7, retrieved 2025-01-08 978-3-540-79566-7 ↩