Spontaneous styrene sulfonate polymerization in Langmuir films: evidence for an anionic mechanism

When a dioctadecyldimethylammonium bromide (DODA) monolayer is spread over styrene sulfonate (SSt) aqueous solution, this monomer was shown to undergo a spontaneous polymerization process which was reported previously. In the present work, this process is followed in real time. The surface pressure variations at constant molecular area (π–t) and/or the molecular area variation at constant surface pressure (A–t) are recorded versus time. The spontaneous polymerization characteristics depend upon the monomer concentration, the surface pressure π, the subphase ionic strength and pH. The polymerization is inhibited by carbon dioxide, sodium bicarbonate and LiClO4. The results presented here show that the polymerization occurs at the interface and that the mechanism is most probably anionic.