An Investigation of the Behavior of Binary Mixed Langmuir Monolayer of 2,2′-p-Phenylenebis (5-phenyloxazol) and Arachidic Acid

Abstract

A systematic study is reported on the monolayer characteristics of 2,2′-p-phenylenebis (5-phenyloxazol) (POPOP) mixed with arachidic acid (AA) at the air-water interface, using surface pressure versus area per molecule (π-A) isotherms complemented with absorption spectroscopy as well as scanning electron microscopy. The (π-A) isotherms of POPOP mixed with AA at different mole fractions show a plateau like region at very low surface pressure, which suggests a phase transition corresponding to a reorientation of the POPOP molecules at the air-water interface. The mixing behavior was obtained from surface pressure-area isotherms by using the surface phase rule and excess area criterion. Results show that POPOP is immiscible in AA, leading to the formation of aggregates. These observations are confirmed by ultraviolet-visible absorption spectroscopy and scanning electron microscopy. Absorption spectra of the mixed LB films reveal that I-type of aggregates play their prominent role in the mixed LB films.