Abstract
The present work reports the synthesis of a stable aqueous magnetic fluid (AMF) by dispersing double-surfactant-coated Fe3O4 magnetic nanoparticles (MNPs) in water using a facile ambient scalable wet chemical route. MNPs do not disperse well in water, resulting in low stability. This was improved by dispersing double-surfactant (oleic acid and sodium oleate)-coated MNPs in water, where cross-linking between the surfactants improves the stability of the AMFs. The stability was probed by rheological measurements and all the AMF samples showed a good long-term stability and stability against a gradient magnetic field. Further, the microwave spin resonance behavior of AMFs was studied in detail by corroborating the experimental results obtained from the ferromagnetic resonance (FMR) technique to theoretical predictions by appropriate fittings. A broad spectrum was perceived for AMFs which indicates strong ferromagnetic characteristics. The resonance field shifted to higher magnetic field values with the decrease in particle size as larger-size MNPs magnetize and demagnetize more easily since their magnetic spins can align in the field direction more definitely. The FMR spectra was fitted to obtain various spin resonance parameters. The asymmetric shapes of the FMR spectra were observed with a decrease in particle sizes, which indicates an increase in relaxation time. The relaxation time increased with a decrease in particle sizes (sample A to D) from 37.2779 ps to 42.8301 ps. Further, a detailed investigation of the structural, morphological, and dc magnetic properties of the AMF samples was performed. Room temperature dc magnetic measurements confirmed the superparamagnetic (SPM) characteristics of the AMF and the M-H plot for each sample was fitted with a Langevin function to obtain the domain magnetization, permeability, and hydrodynamic diameter of the MNPs. The saturation magnetization and coercivity of the AMF samples increased with the increase in dispersed MNPs’ size of the samples. The improvement in the stability and magnetic characteristics makes AMFs suitable candidates for various biomedical applications such as drug delivery, magnetic fluid hyperthermia, and biomedicines.
Highlights
Aqueous magnetic fluids (AMFs) have emerged with great potential due to their substantial development in the field of biomedical applications [1,2,3]
The ferromagnetic resonance (FMR) spectra of all the AMF samples were recorded at room temperature and different microwave spin resonance parameters such as resonance field, peak-to-peak line width (∆H), g-value, spin–spin relaxation time, and spin concentration were calculated by fitting the FMR spectra
This shows that the prepared AMF samples are highly stable for a prolonged period and do not settle down due to gravity
Summary
Aqueous magnetic fluids (AMFs) have emerged with great potential due to their substantial development in the field of biomedical applications [1,2,3]. Reported the preparation of AMFs stabilized by sodium oleate (SO) and dodecylbenzene sulphonic acid (DBSA) They correlated the properties of the AMFs with varying surfactant types both in the presence and absence of externally applied magnetic field. Both DBSA and SO produced a micelle structure and interacted with the surfactant concentration, which resulted in an aggregation of MNPs and a large and fractal-type aggregation observed in the prepared AMFs [27]. The stability of the prepared AMF is probed by rheological measurements both in the absence and presence of the externally applied magnetic field. The present work focuses on solving the grand challenge associated with biomedical applications of AMFs, i.e., technical issues related to the synthesis of AMFs for homogeneous, biocompatible, high magnetic strengths and stable MFs in large-scale production
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