Effect of Cross-linker on the Physicochemical and Stimuli Responsive Behavior of Chitosan-Based Microgels

— This manuscript displays a detailed investigation on the preparation, characterization and physicochemical properties of poly( N -isopropyl acrylamide)-chitosan-poly( N -isopropyl acrylamide)-poly(acrylic acid) represented as [CS-P(NIPAAm-AA)]. Microgels were synthesized by a one-pot approach using ammonium persulfate (APS) as a redox initiator and N , N '-methylenebisacrylamide (MBA) as a crosslinker. Various techniques such as UV–Vis and Fourier transform infrared (FTIR) spectroscopy, dynamic laser light scattering (DLLS), dynamic rheology, Ostwald viscometry, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were used in this study. The synthesized microgels were confirmed by spectroscopic techniques. The temperature-dependent behavior of the microgels was assessed through visual observations, DLLS and rheological measurements. Physico-chemical properties such as storage modulus, shear stress, elasticity, dissipation/loss factor, viscosity, and swelling/de-swelling were studied in the terms of rheological measurements and hydrodynamic radii (Rh) of the microgels. The effect of the amount of cross-linker on these parameters at different temperatures in aqueous media was also studied. In addition, TGA was used to monitor the thermal stability of microgels, while for measuring the surface morphology and approximate particle size of the microgel particles the SEM analysis was performed. Various physico-chemical properties of the described polymeric microgels were observed to be affected by the chemical composition of the microgels, the experimental and solution conditions used.