Project Details
Projekt
Field-induced rotation of ferromagnetic nanorods in hydrogels
Applicant
Dr.-Ing. Andreas Tschöpe
Subject Area
Synthesis and Properties of Functional Materials
Experimental Condensed Matter Physics
Experimental Condensed Matter Physics
Term
from 2013 to 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 237974252
This project is concerned with magnetic composites of Ni-nanorods dispersed in a soft elastic polyacrylamide (PAM) hydrogel. Previous studies focused on the characterization of the Ni nanorods physical properties and their mechanical interaction with the soft elastic matrix. Based on the obtained results, we now investigate the macroscopic deformation of Ni-nanorod/PAM hydrogel composites in homogeneous transversal magnetic fields. First, homogeneous cylinders with a magnetic texture perpendicular to the cylinder axis will be prepared. The field-induced torsion of the cylinders will be measured depending on the orientation of the anisotropy axis with respect to the field direction and the results will be compared with analytic and FEM-based model calculations. The major question to be answered is, how the anisotropy axes of the nanorods in the as-prepared hydrogel cylinder should be oriented to ensure the maximum possible torque for all nanorods at a given field. The answer is directly related to the change in the nanorod axis caused by the macroscopic torsion of the cylinder as well as the local rotation of the individual nanorods in the soft elastic matrix. Our objective is to derive a physical model, based on the microscopic properties of these composites, which enables the optimization of the magnetic texture of torque-based actuators. This approach will also be transferred and applied to the bending of filaments and more complex structures of anisotropy. In addition, 2D layers of Ni-nanorod/hydrogel composites will be prepared by magnetophoretic deposition from colloidal suspension. By applying different gradient fields, the nanorod axis can be aligned either perpendicular or parallel to the deposition plane. Increasing nanorod volume fraction results in an increasing contribution of dipolar interaction to the overall magnetic anisotropy energy and affects the bending of the 2D composite layer.We will continue our investigations on the rotational dynamics of Ni-nanorods in viscoelastic soft matter as contribution to the workgroup ‘rheology’ within the priority program. The current studies of nanorod relaxation in poly-(ethylene glycol) (PEG) solutions of different molecular weight and concentration will be finalized. The dynamic (entangled polymer solutions) or static (chemically cross-linked hydrogels) elasticity associated with the formation of polymer network structures will be characterized based on the oscillation amplitude and relaxation times of the Ni nanorods of variable length. The major objective is to make use of the scale-dependent particle-matrix-interaction for designing ferrogels with viscoelastic properties that are strongly affected and controlled by dipolar field-induced self-assembled network structures of magnetic nanoparticles.
DFG Programme
Priority Programmes
