Homogeneous alignment

In liquid crystals, Homogeneous alignment sometimes called Planar alignment - this is the state of alignment of molecules which is opposite to homeotropic alignment. The molucules here align parallel to a substrate.

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 if this alignment is not entirely clear.