Synthesis, Physicochemical, and Rheological Evaluation of Cellulose-Based Stimuli-Sensitive Polymer Microgels

Abstract

Different samples of PNIPAAm–cellulose–PMAA based microgel were prepared via free-radical polymerization approach under an inert atmosphere. All samples were synthesized using the same precursors: cellulose, N-isopropylacryl amide (NIPAAm), methylene bisacrylamide (MBA) as a cross-linker, methacrylic acid (MAA), and ammonium persulphate (APS) functioning as polymerization initiating agent. However, the amount of reacting species was varied during different formulations. The synthesized microgel samples were thoroughly purified and subjected to a comprehensive suite of characterization techniques, including spectroscopic, rheological, dynamic light scattering (DLS), thermogravimetric analysis (TGA), and some fundamental physiological approaches. Spectroscopic analysis confirmed the successful fabrication of desired polymeric microgels. The storage modulus (G') and loss modulus (G'') of all samples remained constant across the range of angular frequencies tested. Analysis of damping factor (\(\tan \delta \) = G ''/G ') demonstrated that the microgel with a value less than 1 behaved elastic nature, whereas those having a value greater than 1 were highly viscous in nature. The viscosity and shear stress were found dependent on applied shear rates and temperatures. Owing to the thermoresponsive nature of NIPAAm, the gel exhibited lower shear stress rate below its lower critical solution temperature (LCST), while increased hydrophobicity above 30°C led to higher deformation resistance. Light scattering analysis revealed stable hydrodynamic size and dispersion below the pK_a (pH) of MAA across varying temperature. TGA further confirmed the thermal robustness and defined the degradation pattern of the microgel samples. The results indicated that the desired and tunable stimuli-responsive behavior could be effectively modulated by adjusting the feed composition.