화학공학소재연구정보센터
Langmuir, Vol.18, No.17, 6484-6490, 2002
New insights on the interaction mechanism within oppositely charged polymer/surfactant systems
The interactions between dodecyltrimethylammonium bromide and anionic polymers such as neutralized poly(acrylic acid) and methacrylic acid/ethyl acrylate copolymers were investigated using isothermal titration calorimetry (ITC). The ITC results suggest that in the initial stage of titration, the cationic headgroups of surfactant individually bind to the anionic carboxylate groups on the polymer chains due to electrostatic attraction. When the surfactant concentration reaches. a critical value C', the micellization of polymer-bound surfactant occurs, resulting in the formation of insoluble polymer/surfactant complexes. The thermodynamic parameters derived from ITC measurements suggest that the electrostatic binding is an endothermic process driven by entropy. The positive entropy is attributed to the recovery of translational entropy of released counterions by the bound surfactant. The ITC curves for titrations performed in different salt conditions show that addition of salt screens the electrostatic repulsion between surfactant headgroups and attraction between oppositely charged polymer chains and surfactant molecules, which favors the formation of free micelles, and weakens the binding of surfactant onto the polymers.