The complex formed between Cocamidopropyl betaine (CAPB) – sulfonated polystyrene (PSS) via electrostatic and hydrophobic interactions

This work produced a polyelectrolyte, sulfonated polystyrene (PSS) from polystyrene waste. The resulting PSS was characterized by FTIR spectrometry, which shows the bands of the sulfur trioxide group. Thermogravimetric analysis (TGA) confirms the material’s high stability compared to the starting material. The interactions between oppositely charged polyelectrolyte (PSS) and the surfactant cocamidopropyl betaine (CAPB) in an aqueous solution of three different pH values were also studied at 25°C, using conductimetry and viscometry techniques. The CMC of the surfactant is above the critical aggregation concentration (CAC) and well below the C2 (saturation concentration). PSS interacts strongly with the zwitterionic surfactant CAPB. At pH 2.5, the polymer is a strong polyanion, and binding is dominated by electrostatic charge neutralization with the cationic surfactant at this pH. At pH 5.2 and 9, the electrostatic attraction between CAPB and PSS weakens, and the hydrophobic interaction strengthens. The effect of salt concentration on the interaction between CAPB and PSS depends on the competition between increasing interaction and filtering interaction. The ionic strength is essential to these interactions after salt and acid injection. CAC and C2 are affected by the charge of the electrolyte and the medium due to the synergistic effects of alkali on the surfactant compared to the polymer system without alkali-surfactant and probably also due to the increase in the formed bond between the polyelectrolyte and the surfactant in the presence of salt.