CO₂-Induced Interaction between a Pentablock Nonionic Copolymer and an Anionic Fluorocarbon Surfactant

Abstract

A polymer-surfactant complex is significant in understanding the interactions between amphiphilic molecules and has great potential for use in a vast number of industries. In addition, the stimuli-responsive polymersurfactant complex represents a hot research topic for the colloid community. However, the use of CO2 gas to tune their interaction and the corresponding morphological change in the polymer-surfactant complex has been less documented. In this work, the commercially available triblock copolymer Pluronic F127 was used as a starting material and the macromolecular initiator Br-F127-Br was synthesized via esterification. Then, the pentablock copolymer poly(2-(diethylamino)ethyl methacrylate))-block-F127-block-poly(2-(diethylamino)ethyl methacrylate)) (PDEAEAM-b-F127-b-PDEAEMA) was prepared via atom transfer radical polymerization (ATRP) of Br-F127-Br and the monomer 2-(diethylamino)ethyl methacrylate. Both Br-F127-Br and PDEAEAM-b-F127-b-PDEAEMA were characterized by FT-IR and 1 H NMR spectroscopies as well as gel permeation chromatography (GPC). The results indicated that both Br-F127-Br and PDEAEAM-b-F127-b-PDEAEMA were synthesized successfully. The CO2-responsive behavior of the pentablock copolymer was examined by tracking the changes in pH and electrical conductivity of the polymer solution after alternatingly bubbling CO2 and N2. It was found that cyclic streaming of CO2/N2 could alter the pH of the polymer solution between 7.2 and 5.3, leading to the protonation degree of PDEAEAM-b-F127-b-PDEAEMA varying between 0.26 and 0.96; this in turn varied the electrical conductivity of the polymer solution between 19.4 μS•cm −1 and 70.6 μS•cm −1 . The reversible changes in pH and electrical conductivity of the polymer solution indicate the good CO2-stimuli responsiveness of PDEAEAM-b-F127-b-PDEAEMA. The interaction of PDEAEAM-b-F127-b-PDEAEMA with an anionic fluorocarbon surfactant potassium nonafluoro-1-butanesulfonate (C4F9SO3K) with and without CO2 was studied by ultraviolet-visible absorption spectrometry (UV-Vis), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The transmittance of the mixed solution of PDEAEAM-b-F127-b-PDEAEMA and C4F9SO3K could be varied between 84% and 52% in the absence and presence of CO2, indicating the formation of aggregates with different sizes. The DLS results showed that the size of aggregates could be modified reversibly between tens of nanometers and several micrometers by bubbling CO2 and replacing CO2 by N2. The TEM image revealed the reversible morphological transition of the aggregates from spherical to wormlike micelles after bubbling CO2. The carbonic acid formed from CO2 and water can protonate the PDEAEMA in the pentablock copolymer to form PDEAEMA•H + , and thus the interaction between the pentablock copolymer and C4F9SO3K becomes strong. When CO2 is replaced by N2, PDEAEMA•H + reverts to PDEAEMA, and the interaction becomes weak once again. It can therefore be concluded that the protonation/deprotonation process of the pentablock copoly...