Impact of graphene oxide on the magnetorheological behaviour of BaFe12O19 nanoparticles filled polyacrylamide hydrogel

Abstract

Development of magneto-sensitive smart hydrogels based on crosslinked polyacrylamide (PA) mixed with either nanoparticles of barium ferrite (BaM) or combinations of both BaM and graphene oxide (GO), as nanosheets, have been carried out. Spherical BaM particles with an average crystallite size of 46.63 nm were synthesized using an ultrasonic assisted novel coprecipitation method. Thin films of isotropic PA hydrogel nanocomposites were obtained by solution casting of in-situ polymerized mixture of acrylamide, N,N methylene bisacrylamide monomer (crosslinker) and a redox initiator and the fillers, as above. Variety of characterization techniques viz., XRD, for determination of crystal structure of nanofillers; X-ray photoelectron spectroscopy, for determination of chemical composition and oxidation state of elements in BaM; FTIR, for interaction of BaM and GO with polymer matrix; DSC, for determination of glass transition temperature and FESEM and TEM, for correlation of morphological features with the magnetorheological (MR) properties were used. MR studies were conducted in a parallel plate rheometer and the composites were found to exhibit both negative and positive MR effects depending on concentration and dispersion of the fillers added to the polymer. High surface energy and permanent magnetization of the nanoparticles lead to formation of large clusters interconnected through bridges. The positive MR effect at very low concentration of BaM is attributed to the localized hardening of the polymer matrix by the heterogeneously dispersed BaM clusters. Addition of GO along with BaM improves further the dispersion of BaM nanoparticles but the negative MR effect still holds up to 10 wt% loading of BaM. However, increase in BaM loading to 20 wt% in presence of GO leads to a positive MR effect. This is due to higher concentration of BaM which formed a continuous network of nanoparticles and the shear stress could not break the connectivity between the nanoparticles resulting in a positive MR effect.