Anisotropic and rough

Researchers at Kent State University have uncovered the mechanisms of liquid crystal alignment, a puzzle scientists have not been able to explain for more than 30 years.


Researchers at KentStateUniversity, headed by Dr. Satyendra Kumar, professor of physics, have uncovered the mechanisms of liquid crystal alignment, a puzzle scientists have not been able to explain for more than 30 years.



The alignment of liquid crystals in devices such as laptop computers and palm pilots makes the displays on these devices readable.



All substrates used in liquid crystal displays (LCDs) have anisotropic surface roughness. Such a surface is smooth along the grooves but rough in the perpendicular direction. When liquid crystal molecules in LCDs find themselves near such a surface, they orient parallel to the “smooth” direction. This is true of all surfaces, irrespective of the nature of the surface and the treatment method used to prepare it.



In order to make LCDs work, companies have aligned liquid crystal molecules with the optic axis in liquid crystal displays. The most common method used requires glass plates coated with a polymer that are mechanically “rubbed” with a linen cloth.



The surface becomes smooth along the rubbing direction and the LCD’s optic axis aligns along the rubbing direction. Several methods other than rubbing have also been developed, including UV treatment and plasma exposure. The results show that even when the surface is untouched but exposed to polarised UV, it develops a structure that is anisotropic and rough.