Shear modulus of two-dimensional colloidal crystals
Universität Konstanz, Fachbereich Physik, Fach M 621
D-78457 Konstanz, Germany
2 Institut C. Sadron, CNRS - 6 rue Boussingault F-67083 Strasbourg Cedex, France
Accepted: 25 October 2001
A new method for the determination of elastic constants of colloidal systems is described. We study super-paramagnetic microspheres confined by gravity to a two-dimensional layer at a water-air interface. Under an external vertical magnetic field the particles arrange in a crystalline triangular phase because of the repulsive dipole-dipole interaction. By use of an optical tweezer, one triangle formed by three spheres is rotated from its equilibrium position and the relaxation time measured using video-microscopy. We demonstrate that this time is directly related to the shear modulus μ of the crystal and study μ as a function of the magnetic particle interaction strength.
PACS: 62.20.Dc – Elasticity, elastic constants / 82.70.Dd – Colloids
© EDP Sciences, 2002