Complexes of an anionic poly(p-phenylene) polyelectrolyte and dioctadecylammonium bromide at the air–water interface

By spreading dioctadecyldimethylammonium bromide on a subphase containing rigid rod-like anionic poly(p-phenylene) sulfonate, a complex monolayer is formed in situ at the air–water interface. Complexation results in an increase of the area per amphiphile molecule compared to the amphiphile on pure water. The change in structural order upon complexation and subsequent compression of the monolayer can be demonstrated employing UV/Vis spectroscopy: A red-shift of the polymer absorption band upon compression and a subsequent partial reversion of this shift after monolayer collapse can be observed. The peak shift is discussed to be a result of the electronic interaction of the π-systems (aggregation) or to be due to a planarisation caused by changes in intramolecular and intermolecular interaction upon complexation and compression. Both explanations require the formation of a highly ordered monolayer structure with increasing surface pressure. Upon collapse of the monolayer, the structure relaxes. Investigation of the complex Langmuir–Blodgett (LB) films employing UV/Vis spectroscopy gives further information about the structural order. XPS measurements reveal that a stoichiometric complex is formed.