ESTIMATION OF MICROSCOPIC RUBBING ALIGNMENT PARAMETERS

We report an examination of the cloth-rubbing process, widely used to effect liquid crystal alignment, from a simplified microscopic perspec tive. We define strength of rubbing by the average applied force per r ubbing fibre (approximately 11-22 mu N under our conditions, assuming all fibres passing the surface make contact), and extent of rubbing by the fraction of total surface area contacted during the process. Fibr e-surface microscopic contact widths estimated from atomic force micro scopy images of rubbed alignment polymer surfaces were in the range 10 -500 nm. Taking 100 nm as an average value, we show that the entire al ignment surface may be contacted several times during a typical rubbin g process. Fibre-surface contact shear stresses can approach the GPa r ange, several orders of magnitude greater than the macroscopic rubbing pressure.