Berlin 2012 – scientific programme

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MA: Fachverband Magnetismus

MA 17: Magnetic Measurement Methods

MA 17.4: Talk

Tuesday, March 27, 2012, 12:30–12:45, EB 202

Estimation of the shear modulus of hydrogels by magneto-optical transmission measurements using ferromagnetic nanorods as probes — •Christoph Schopphoven, Andreas Tschöpe, Philipp Bender, and Rainer Birringer — Universität des Saarlandes, Saarbrücken, Deutschland

Nickel nanorods are synthesized by electrodeposition of nickel into porous alumina templates, and released by dissolving the alumina, using a surfactant to prevent agglomeration. The rods are then dispersed in gelatin sols at 60°C and alligned by applying a magnetic field, which is maintained during subsequent cooling to obtain magnetically textured ferrogels. When a transversal magnetic field is applied perpendicular to the rod axis, a magnetic torque rotates the particles in field direction. With increasing rotation angle the mechanical torque associated with the elastic deformation of the matrix increases until a balance between mechanical and magnetic torque is reached. Due to their cylindrical shape, the nanorods also exhibit significantly different electrical polarizabilities along the principal axes. As a result, the extinction of polarized light depends on the orientation of the nanorods with respect to the polarization direction of the incident light, which allows to determine the equilibrium rotation angle of the nanorods. Measurements of optical transmission as a function of applied magnetic field are exploited to obtain the shear modulus of the gel matrix.