Temperature-Responsive Aqueous Two-Phase System Based on Cationic Polyelectrolytes for Polymer Microspheres...

Polymer microspheres are typically prepared via emulsion methods that rely on organic solvents, leading to environmental concerns and separation challenges. Aqueous two-phase systems (ATPS), based on water-water phase separation, offer a sustainable and environmentally benign alternative. However, a key challenge lies in responsive formation and in situ solidification of aqueous droplets. In this work, a temperature-responsive and self-curable ATPS is developed. Poly(1-cyanomethyl-3-vinylimidazolium bromide) (PILCN) and poly(diallyldimethylammonium chloride) (PDDA) undergo liquid-liquid phase separation (LLPS) at low temperature, forming PILCN-rich droplets. Upon heating, the system transitions into a homogeneous phase, followed by adjustment to mildly alkaline conditions, which triggers in situ self-crosslinking of PILCN and leads to the formation of solid microspheres. The size and morphology of the microspheres can be effectively tuned by pH, temperature, and concentration, while the formation process is dictated by the competitive interplay between LLPS and cyano crosslinking. The resulting PILCN microspheres exhibit excellent adsorption performance toward tetracycline, with a maximum adsorption capacity of 826.5 mg/g. The adsorption behavior is well-described by the Langmuir isotherm and pseudo-second-order kinetic models, suggesting monolayer adsorption is predominantly governed by chemisorption. The adsorption process arises from a synergistic combination of electrostatic interactions, hydrogen bonding, π-π interactions, and cation-π interactions.