Cocamidopropyl Betaine Can Behave as a Cationic Surfactant and Electrostatically Associate with Polyacids of High Molecular Weight
Matheus Ouverney Ferreira, Huliana Francisca Câmara de Assis e Ana Maria Percebom
Many practical applications, especially cosmetics, use mixtures of zwitterionic surfactants with polymers, but the scarcity of studies limits the control of their mixture properties. In the specific case of cocamidopropyl betaine (CAPB) and polyanions, the occurrence of phase separation with no previous characterization and the lack of knowledge of the involved parameters motivated the present study. Comparison of mixtures of CAPB with polyacrylic acid (PAA) of different chain lengths indicated phase separation only occurs if the chain is long enough to promote bridging. Surface tension measurements confirmed the aggregation between CAPB and PAA, but not at neutral pH. Scattering techniques allowed to elucidate the structures formed by CAPB with the polymers at different conditions. The results demonstrate that the association between PAA and CAPB occurs even when the polymeric chain is short because PAA reduces the pH and the protonated form of CAPB behaves as a cationic surfactant. However, there is no bridging when the micelles are associated with short chains, being still water-soluble. In conclusion, low pH is important for the association between CAPB and PAA, but high degree of polymerization is a requirement for the phase separation, whereas ionic strength is not essential for these phenomena.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | 2022