The effect of adding cobalt ferrite (CoFe3O4) nanoparticles as fillers on rheological and structural behaviour of gum ghatti-cl-poly(NIPAm) hydrogels

Abstract

The objective of this study was to synthesize a Gum Ghatti-cl-poly(NIPAm)/CoFe₂O₄ (GGNICAF) hydrogel through free radical copolymerization. The key components used in the synthesis included gum ghatti as a biopolymer (GG), methylene bis-acrylamide (MBA), Potassium Persulfate (KPS), and Ammonium Persulfate (APS) as a cross-linker. Additionally, varying quantities (0–50 mg) of cobalt ferrite (CoFe₂O₄) magnetic nanoparticles (CFMNPs) were incorporated as fillers, synthesized through a coprecipitation route.

The hydrogels were characterized using TGA and FTIR studies. Notably, the swelling study in water demonstrated remarkable water absorption properties. Rheological properties were observed at room temperature using a rheometer with a parallel plate at a 1 mm gap. The rheological and microstructural behavior of the composites were investigated through steady-state flow curves, creep-recovery tests, and small amplitude oscillatory shear tests.

Higher biopolymer content in the mixtures resulted in a more elastic and compact structure, characterized by higher values of both \(\mathrm{G}'\) and \(\mathrm{G}''\). Flow curves indicated shear-thinning behavior. Oscillatory tests revealed an increase in the strength of the hydrogel network with higher crosslinker concentrations, decreasing at low polymer concentrations. Within the linear viscoelastic region (LVR), \(\mathrm{G}'\) values consistently exceeded \(\mathrm{G}''\), indicating a predominantly elastic character. Tan \(\delta \) values consistently remained below one, signifying an elastic structure throughout a wide range of concentrations (0–5) for all GGNIPACF samples.

Viscosity vs. shear rate profiles were assessed using the Power Law model, while shear stress vs. shear rate curves were analyzed using the Bingham model and Herschel-Bulkley model.