A Study on the Thermodynamic Properties of Interaction between Poly(acrylic acid) and n-Octyltetraoxyethylene

Polymer–surfactant mixtures have been used in a wide range of commercial applications. Therefore, their behavior is of great interest. In this study, isothermal titration calorimeter (ITC), surface tension and pH meter are applied to investigate the interaction between the surfactant n-octyltetraoxyethylene (C8E4) and the weakly dissociated polyelectrolyte, poly(acrylic acid) (PAA). When the surfactant C8E4 is added into the PAA solution, the critical aggregation concentration (CA) is defined as the onset concentration of binding surfactant onto polymer. While surfactant is further added into the system until polymer is saturated with bound surfactant. That defines the saturation concentration (Cs). The second critical micelle concentration (Cm) is then defined as the concentration where the surfactant starts to form free micelles beyond the saturation concentration. In this study: ITC, surface tension and pH data are applied to extract the information of CA, Cs and Cm. The consistency between these three methods is carefully examined and discussed.