Surface free energy and pretilt angle on rubbed polyimide surfaces

To investigate surface free energy of rubbed polyimide surfaces as a function of the rubbing strength, we measured the contact angle of distilled water and methylene iodide on the polyimide surfaces. For this purpose, a main-chain-type and two side-chain-type polyimides were used. The dispersion force (γ^d) and the polar force (γ ^p) of the rubbed polyimide surfaces was measured. The rubbing induced polarity on the polyimide surfaces. Also, polar forces contributed to form a pretilt angle of liquid crystals on the rubbed polyimide surfaces. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 267–271, 1999