ORIENTED FILMS FROM POLYMERIC AMPHIPHILES WITH MESOGENIC GROUPS - LANGMUIR-BLODGETT LIQUID-CRYSTALS

Langmuir-Blodgett films prepared from performed amphiphilic polymers containing mesogenic chromophores ("amphotropic" polymers) exhibit a phase change to a less ordered state on heating. This reversible transition occurs at the same temperature as the onset of liquid-crystal formation in the bulk material. Spectroscopic and ellipsometric characterization provides quantitative information on the chromophore orientation in the films as a function of temperature. These results show a highly ordered aggregated structure at room temperature with a sharp transition to a more mobile state at about 60-degrees-C. The chromophores are then no longer aggregated and exhibit a broader distribution of orientations, although on the average they are still quite highly aligned. This behavior is similar to liquid-crystal formation in bulk materials and opens the possibility of inducing monodomain formation in Langmuir-Blodgett films. For the polymer studied in most detail, the liquid-crystal-like condition persists in the films up to the highest temperature studied, ca. 150-degrees-C in contrast to the bulk material that becomes isotropic by 84-degrees-C. The ordered aggregated structure is recovered reversibly on cooling even from the highest temperature without loss of film integrity, demonstrating an enhanced stabilization in the Langmuir-Blodgett film environment.