Effect of Distribution of Functionalized Magnetic Nanoparticles on Ferrogel Actuation

The ferrogels elongate, contract, and deflect in response to an applied magnetic field. In order to study its response to magnetic fields, ferrogels were prepared using meghamite (Fe304) nanoparticles (size ∼ 10–25 nm) using the hydrogel based on N-isopropylacrylamide (NIPAm). The particle distribution is determined for different cross-linking density of the gel in the range of 2% to 8%. The ferrogels were analyzed using ultra small angle x-ray scattering (USAXS) and the particle distribution were compared with direct imaging of the samples using transmission electron microscopy. The uniformity of the distribution of the particles for different samples prepared was determined using USAXS. Magnetic characteristics of the ferrogel were determined using a direct current superconducting quantum interference device (DC-Squid). The magnetic moments of the polyvinylpyrrolidone (PVP) coated Fe₃O₄ nanoparticles based ferrogel are reduced from 2.5 – 0.4 emu/g, as the particle concentration is decreased from 8.75 to 1.25%. Subsequently, the deflection and strain also reduced under static magnetic field. These studies showed that a maximum deflection of 20% and strain of 10% to its original value could be achieved by varying the particle size and/or distribution. The crosslinking ratio of the polymer was varied from 1.2 – 8%. The deflection and elongation characteristics were studied using a custom-built electromagnetic set-up with a pole gap of 10 mm with magnetic field strength up to 2500 Gauss. However, the maximum strain reduces as the crosslinking density increases. This study clearly shows the dependence of the deflection and strain on the functionalization material coated on the particle. Details of the results of our experiments are presented in this paper.