Preparation of Submicrometer-Sized Quaternary Ammonium-Based Poly(ionic liquid) Particles via Emulsion Polymerization and Switchable Responsiveness of Emulsion Film

Emulsion polymerization of ionic liquid monomer [2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)amide ([MTMA][TFSA]) was performed. In the presence of potassium persulfate and sodium dodecyl sulfate as the ionic initiator and emulsifier, respectively, the system was colloidally unstable and coagulated, owing to anion exchange between the ionic liquid monomer and ionic emulsifier. When a nonionic initiator and emulsifier were used (2,2′-azobis 2-methyl-[1,1-bis(hydroxymethyl)-2-hydroxyethylpropionamide]; VA-080, polyoxyethylenesorbitan monooleate; Tween 80, respectively), a stable emulsion was obtained without coagulation, and the zeta potential of the prepared particles exhibited a high positive charge. Utilizing this surface charge, poly([MTMA][TFSA]) (PIL) particles were then successfully prepared via emulsifier-free emulsion polymerization without an ionic initiator. Moreover, the contact angle of water on the PIL emulsion film (emulsifier-free emulsion polymerization) was found to be ∼70° (static measurement), indicating that the surface of the PIL film was relatively hydrophobic. The retreating contact angle (∼28°) also indicated water wettability. However, when water was dropped on the PIL film just after the water already on the surface had completely retreated, the PIL film was instantaneously hydrophobic again. This result suggests that responsiveness of the PIL emulsion film was switchable between hydrophobic (in air) and hydrophilic (in water).