Interfacial behavior of randomly charged sulfonated polystyrene (PSS) at the air/water interface

Langmuir monolayers of randomly charged polystyrene sulfonated acid, PSSx, with various degrees of sulfonation (x) ranging from 4 up to 35% were studied. Three characteristic regimes of PSSx were determined, according to the balance between electrostatic and hydrophobic interactions in these ranges. Low charged PSS (4–5%) aggregates to irreversible films upon compression, leading to strong hysteresis. Moderately charged PSS (6–16%) is shown to less hysteretic. In contrast, highly charged PSS (35%) formed a reversible film due to dominant electrostatic interactions over hydrophobic interaction. Using in situ neutron reflectivity (NR) we observed that PSS with 35% sulfonation formed a highly stretched brush into the water subphase upon compression.