Enhancement in field induced heating efficiency of TMAOH coated superparamagnetic Fe3O4 nanoparticles by texturing under a static bias field

Abstract

We demonstrate ~36% enhancement in heating efficiency in an aqueous magnetic fluid containing tetramethyl ammonium hydroxide (TMAOH) coated superparamagnetic (SPM) Fe3O4 nanoparticles (MNPs), after external static bias field (HDC ~ 80 Oe) induced in situ texturing, parallel to the radio frequency alternating magnetic field (RFAMF). Under the influence of HDC, the dispersed SPM MNPs undergo a disorder-to-order transition by forming linear chain-like structures parallel to the direction of HDC, which is confirmed from atomic force microscopy images. Using flexible chain model, the ensemble averaged chain length is determined and formation of such chains is found to enhance the effective anisotropy energy density by ~24%. Calorimetric experiments show ~8–15 and 26–36% enhancement in RFAMF induced heating efficiency for the oriented ferrofluids with MNP concentrations of 6 and 8 wt%, respectively. High frequency dynamic hysteresis loops simulated for the oriented samples indicate ~37% enhancement in heating efficiency over the randomly oriented samples, which is found to be in good agreement with the experimental results. Our findings validate the recently proposed in situ orientation protocol for enhancing RFAMF induced heating efficiency and provide further impetus towards successful implementation of magnetic fluid hyperthermia for cancer therapy by minimizing exposure time and offering new opportunities to mitigate the undesired loss of heating efficiency in viscous tissue-like environments.