(The) preparation and transfer characteristics of polymide langmuir-blodgett film for liquid crystal alignment

Abstract

The stabilities of the monolayers of the two kinds of polyamic acid alkylamine salts (PAAS) were investigated as a function of the alkyl chain length of alkylamine and pH, and the characteristics of the LB film were determined. The stability increases as the chain length of salts increases and the hysteresis of the isotherms is found. The transferabilities of the monolayers were sharply influenced by the stability at the interface, but not affected by the dipping conditions, i.e., the width of the substrate (up to 45 mm) and the dipping speed (up to 30 mm/min). In a well balanced condition, the Langmuir film is transferred as a Y-type on various substrates. The transferred multilayers of PAAS were converted to the polyimide (PI) film only by a thermal heating. The thickness of PAAS was found to be $16.7 \mbox{\AA}$, but during imidization, reduced to $5.6 \mbox{\AA}$ per layer in average, and no ordering of PI film was found. Finally, it``s also found that the surface free energy of PAAS LB film is lowered when PAAS films are converted to PI. In LC cell, the film of PAAS(SE-150) showed better alignment of liquid crystals than that of PAAS(PMDA-3,3``-ODA).