POLAR POLYMERIC LANGMUIR-BLODGETT-FILMS CONTAINING NITROBIPHENYL GROUPS

Side-chain liquid crystalline copolymers containing nitrobiphenyl were used to fabricate polar Langmuir multilayers. (Methoxyethoxy)methoxy terminal groups were incorporated in the copolymers to enhance the spr eadability and monolayer formation of the copolymers. X-ray diffractio n, second harmonic measurements, and pyroelectric studies all support the existence of a noncentrosymmetric structure for the polymeric mult ilayers. Thus, the possibility of using polymeric monolayers to preven t molecular turnaround upon X-type horizontal deposition was demonstra ted. The molecular susceptibility for nitrobiphenyl was measured to be (9.8 +/- 1.0) X 10(-30) esu. The linear relationship between the squa re root of the second harmonic intensity (pp) and the number of layers (see Schemes I-V) indicates the good quality of the multilayers. The copolymeric multilayers with shorter spacers (see Schemes I-V) were fo und to have a lower second harmonic response. An unusual pyroelectric response was observed for Cop11 multilayers. The pyroelectric coeffici ents were determined to be 2.85 X 10(-10) C cm-2 degrees-C-1 for Cop11 and 2.0 X 10(-10) C cm-2 degrees-C-1 for Cop4. FTIR-RA studies show t hat the aromatic rings of Cop4 and Cop11 multilayers stay oriented in liquid crystalline phases.