Thermodynamic Study on Upper Critical Solution Temperature (UCST) Behavior of Polyguanidinium in Aqueous Midea
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Liquid-liquid phase separation (LLPS) in aqueous solutions of polyguanidinium (G) induced by salt addition, displaying upper critical solution temperature (UCST) phase behavior. In this work, we characterize the UCST behavior of G aqueous solutions using transmittance, light scattering and small-angle neutron scattering, providing phase diagrams and the pertinent thermodynamic parameters. The phase separation boundaries gradually increase across a wide temperature range as salt concentration increases. Also, theta temperature (Tθ) and effective interaction parameter (χeff) for G solutions are quantitatively modulated with salt concentration. These results indicate that the attractive monomer-monomer interactions via pi-pi interactions of guanidinium groups can be precisely controlled by salt concentration, leading to the UCST behavior. Our findings provide thermodynamic insights into the role of associative interactions for LLPS that exhibits UCST phase behavior in aqueous media.