Aggregation Behavior of Amphiphilic Statistical Polymers and Their Interactions with Nonionic Surfactants

A series of amphiphilic polymers were synthesized by the statistical polymerization of 2-(acrylamido)-dodecanesulfonic acid (AMC(12)S) with 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) and they contained a high mole fraction of AMC(12)S (X=0.1, 0.3, 0.5). The aggregation behaviors of the polymers and their interactions with three nonionic surfactants HO(CH2CH2O)(10)C12H25 (C12E10), HO(CH2CH2O)(20)C12H25 (C12E20), and HO(CH2CH2O)(40)C12H25 (C12E40) in aqueous solutions were investigated by steady-state fluorescence and quasi-elastic light scattering measurements. The effect of X on the association performance and the influence of the surfactant's hydrophilic group length on these interactions were also investigated. The critical aggregation concentration (CAC) of the polymer was found to significantly decrease with increasing X. The CAC of the polymer with X=0.5 is as low as 0.0039 g.L-1. The hydrodynamic sizes of the aggregates (R-h) are larger than 26 nm, and increase with an increase in polymer concentration, indicating that the polymeric molecules exhibit a strong tendency for interpolymer association, leading to the formation of multimolecular aggregates. When X increases, both R-h and its tendency to increase decrease, suggesting that the aggregates become more compact. The interaction between surfactant and polymer is very strong and the polymer aggregates begin to collapse when the surfactant concentration reaches the critical micelle concentration (CMC) in the mixed solutions and mixed aggregates form. The destructive ability of the surfactant increases as the length of the hydrophilic group increases. The R-h value of the mixed aggregates formed by C12E40 and the polymer with X=0.5 is 6.8 nm, which is consistent with the R-h value of the C12E40 aggregates.