Macroscopic and mesoscopic patterns observed in thin films formed due to polymerization of aniline at the air–water interface

Abstract

We report two-dimensional mesoscopic and macroscopic patterns observed in thin films formed due to polymerization of aniline at the air–water interface. The polymerization at the interface was coupled to a reaction in the bulk medium that was either an iron (ferroin)-catalyzed Belousov–Zhabotinsky (BZ) reaction or another reaction condition where the ferroin component of BZ reaction was replaced by FeSO₄ or Mohr's salt [(NH₄)₂SO₄·FeSO₄·6H₂O]. Also, a simple mixture of KBrO₃ and KBr in aqueous acidic solution produced patterned polymers at the interface, observed with aniline introduced from both the vapor phase and the bulk phase (by dissolving in H₂SO₄). Observation under an optical microscope revealed that the macroscopic patterns consisted of mesoscopic patterns of various geometrical shapes. In one case, regular circular mesoscopic patterned polymer growth was observed when the reaction was carried out in the presence of 2.02 mM sodium dodecyl sulfate. On the other hand, when the film was grown in an ultrasonicator bath there were no observable mesoscopic or macroscopic patterns in the film.