Dresden 2009 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 19: Focus: Magnetic Soft Matter I

CPP 19.4: Invited Talk

Tuesday, March 24, 2009, 11:00–11:30, ZEU 222

Mechanical Properties of Uniaxial Magnetic Gels — •Philippe Martinoty — Institut Charles Sadron, Strasbourg, France

Magnetic gels are composite materials made up of magnetic particles embedded in a polymeric matrix. They are called uniaxial when the magnetic particles are oriented in a permanent way in a given direction.

Two questions are crucial for optimizing uniaxial magnetic gels: how they are formed, and what are their responses to a mechanical field? However, these questions remained unstudied, essentially because the conventional rheometers do not allow performing shear measurements under magnetic field. Here we show some results taken during the formation process of a uniaxial magnetic gel and on the formed material with the piezoelectric rheometer we have recently developed.

This apparatus enables to take measurements of the complex shear modulus in a wide frequency range and for very weak applied strains. The kinetics of formation of the gel was followed by placing the cell in the air-gap of an electromagnet, and the organization of the magnetic particles observed by placing the cell under an optical microscope. Two types of uniaxial magnetic gel were studied; an aqueous gel based on a commercial ferrofluid, and an organic gel containing magnetite particles. This presentation is rounded off by a comparison with the mechanical properties of liquid crystal elastomers.