Surface pressure and surface potential isotherms of ytterbium bisphthalocyanine Langmuir monolayers

A systematic study is reported on the monolayer characteristics of ytterbiu m bisphthalocyanine (YbPc2) at the air-water interface, using surface press ure and surface potential isotherms. The influence of various experimental parameters was analyzed, including compression speed, spreading volume, pos ition of the pressure sensor, and subphase temperature. The area per molecu le decreased with increasing spreading volumes. Interestingly, the position of the Wilhelmy plate affected the pressure-area isotherms, which does not occur for traditional aliphatic compounds. No significant influence from t he subphase temperature was detected. Upon varying the compression speed, t he surface potential curve and the collapse pressure were affected, even th ough the area per molecule remained practically the same. When these monola yers with distinct dipole moments were transferred onto a gold-coated glass substrate, the resulting multilayer LB films exhibited the same surface po tential, probably:due to molecular rearrangement upon transfer.