Thermal and Structural Analysis of Cross-Linking Dynamics in Polyzwitterion/ChCl Blends

Polyzwitterions (PZIs) form intra- and inter-chain crosslinks due to presence of cationic and anionic units on each side group. Dissociated salt ions disrupt the crosslinks through electrostatic shielding, reducing molecular confinement and inducing strong hydration. The dense hydration layer formed at the zwitterionic moieties and the hydrophobic PZI backbone drive self-assembly of micellar structures that resist protein absorption and, in filtration membranes, exhibit strong anti-fouling properties. Choline chloride (ChCl) was blended with poly(sulfobetaine acrylate) (PSBA) at different molar ratios of PZI monomeric units to salt. Structural and thermal analysis determined the confinement of each blend. Wide-angle X-ray scattering measured the PSBA amorphous halo’s peak position and width. Peak broadening would indicate decreased confinement. Fourier-transform infrared spectroscopy showed whether confinement was due to ChCl ion and zwitterionic moiety interaction. Thermogravimetric analysis provided the degradation profile of each blend, while differential scanning calorimetry measured bound water content, glass transition temperature (Tg), and heat capacity increment at Tg. Increased heat capacity increment has been shown to be a direct indicator of molecular confinement [1].

[1] Thomas, J., Chum, S., Deucher, W., Mondal, A., Asatekin, A., & Cebe, P. Thermal and structural properties of polyzwitterions: Effects of monomer chemistry and salt addition. Thermochimica Acta. (2023) 730, 179617.