Material-independent determination of anchoring properties on rubbed polyimide surfaces

A material-independent method for determining liquid-crystal (LC) anchoring energy on rubbed polyimide (PI) surfaces has been devised. This method exp loits the changes in the easy axis of rubbed PI film induced by exposure to linearly polarized UV (LPUV) Light. The distribution of PI chains in a rub bed film is approximated by a Gaussian function and its width determined fr om the measured rotation of the LC easy axis as a function of exposure time . A quasimicroscopic free energy of the LC-substrate interface is used to m odel LC anchoring properties. The experimental and calculated values of the azimuthal anchoring energy are in good agreement and found to depend inver sely on the width of the distribution function. The measurements of the wid th of the chain distribution function provide a simple LC material-independ ent method for determining the LC anchoring properties. With this method, i t is also possible to calculate the strength of the interaction between PI chains and LC molecules. [S1063-651X(99)04612-7].