Phase behavior and micellar properties of carboxylic acid end group modified pluronic surfactants

The micellar behavior of three different carboxylic acid end standing (CAE) surfactants has been characterized using conductometry, differential scanning calorimetry, isothermal titration calorimetry, and dynamic light scattering. The CAE surfactants are modified high molecular weight Pluronic (PEO-PPO-PEO triblock copolymer) surfactants. The influence of pH and salt additives on the critical micellization temperature (CMT) and the cloud point of the CAE surfactants have been studied. Both the CMT and the cloud points of the CAE surfactants increase as a function of pH and decrease as a function of ionic strength. For the CAE surfactants, the CMT varies by about 5 °C, and the cloud point shows a variation in the order of 20-30 °C, as compared to the unmodified Pluronics. From the different experimental techniques, it follows that at low pH values (pH <3.5), the CAE surfactants show the same micellar behavior as the unmodified Pluronic, while at high pH values (pH > 6), the micellar properties of the CAE surfactants are considerably different from those observed for the corresponding Pluronic. It has been demonstrated that the CAE micelles are capable of removing simultaneously divalent ions and phenanthrane. The CAE surfactants are the first known anionic surfactants that show cloud point behavior with the addition of low concentrations of simple salts, such as, for example, NaCl.