Loading of PNIPAM Based Microgels with CoFe₂O₄ Nanoparticles and Their Magnetic Response in Bulk and at Surfaces

Abstract

The present paper addresses the loading of thermoresponsive poly-N-isopropylacrylamide (PNIPAM) based microgel particles with magnetic nanoparticles (MNP: CoFe2O4@PAA (PAA = poly(acrylic acid))) and their response to an external magnetic field. The MNP uptake is analyzed by transmission electron microscopy (TEM). Obviously, the charge combination of MNP and microgels plays an important role for the MNP uptake, but it does not explain the whole uptake process. The MNP uptake results in changes of size and electrophoretic mobility, which is investigated by dynamic light scattering (DLS) and a Zetasizer. The microgels loaded with MNP preserve their thermosensitivity, and they show magnetic separability and are considered as magnetic microgels. After adsorption at a surface the magnetic microgels are studied with a scanning force microscope and indentation experiments. The magnetic microgels show an elongation along the magnetic field parallel to the surface while the height of the microgels (perpendicular to the surface and to the magnetic field) is compressed. This result is in good agreement with simulations of volume change of ferrogels in a magnetic field.

The influence of an applied magnetic field on the self-assembly of magnetic nanogels

“…In difference with other responsive behaviours, that are mainly associated to the physical and chemical properties of the polymers forming the soft particle, a response to external magnetic fields can be settled for micro-and nanogels by embedding magnetic nanoparticles into the polymer network. This idea was introduced for the creation of macroscopic magnetic gels [38][39][40][41][42][43][44][45] and soon adopted for the synthesis of microscopic gel particles [46,47]. The use of magnetic fields as control stimuli allows to avoid possible side effects induced by changing parameters to which many soft matter substancesparticularly biochemical compounds-are sensitive, such as pH or electric field.…”

Characterization and phase‐transition behavior of thermoresponsive PVME nanogels in the presence of cellulose nanowhiskers: Rheology, morphology, and FTIR studies

“…Hydrogels are chemically or physically crosslinked polymer networks with the ability to absorb considerable amounts of water and can be either in the form of macroscopic networks or in smaller dimensions like microgels or nanogels . Smart hydrogels can respond to external stimuli such as temperature, PH, light, magnetic field, and so forth and their physicochemical properties such as water solubility, shape, volume and optical properties can change in response to such stimuli . For example, in temperature sensitive hydrogels, increasing the temperature above the lower critical solution temperature (LCST) results in a significant decrease in the system volume .…”

The effect of magnetic nanoparticle concentration on the structure organisation of a microferrogel

“…Microferrogels (magnetic microgels, microscopic ferrogels, MFGs) are isolated soft polymers objects with typical sizes in the range of 0.1-10 μm containing embedded magnetic nanoparticles (NPs); typical NP materials are magnetite and cobalt ferrite [1,2]. Strong coupling between the magnetic NPs and the polymer mesh, in which the NPs take on the role of cross-linkers, ensures the dependence of mechanical and structural properties of a MFG object on the external magnetic field.…”