The results of a Kent State study of a variety of glass substrates of the type used in liquid crystal displays (LCDs) revealed for the first time the way liquid crystals align. All substrates used in 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 also have been developed, including UV treatment and plasma exposure. The results show that even when the surface is untouched but exposed to polarized UV, it develops a structure that is anisotropic and rough.
This research was performed over the past 10 years and appeared as a report in the Feb. 25, 2005, issue of the prestigious journal Physical Review Letters.
For more information, Dr. Kumar can be reached directly at 330-672-2566 or skumar@kent.edu .
Physical Review Letters