Thu, 24 Jul 2008 22:02:25 BST CiteULike: di dchen Tierno http://www.citeulike.org/user/dchen/author/Tierno CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/dchen/article/2766831 <i>Physical Review Letters, Vol. 100, No. 14. (2008)</i><br /><br />We investigate the collective organization of paramagnetic colloidal particles externally driven above the periodic stripes of a uniaxial ferrimagnetic garnet film. An external field modulation induces vibration of the stripe walls and produces random motion of the particles. Defects in the stripe pattern break the symmetry of the potential and favor particle nucleation into large clusters above a critical density. Mismatch between particle size and pattern wavelength generates assemblies with different morphological order. At even higher field strengths, repulsive dipolar interactions between the particles induce cluster melting. We propose a novel approach to generate and externally control a variety of colloidal assemblies. Colloidal Assembly on Magnetically Vibrated Stripes Pietro Tierno Thomas Fischer Tom Johansen Francesc Sagués doi:10.1103/PhysRevLett.100.148304 Physical Review Letters, Vol. 100, No. 14. (2008) 2008-05-07T15:36:01-00:00 2008 Physical Review Letters 100 14 APS clusters colloids magnetic http://www.citeulike.org/user/dchen/article/2563145 <i>Physical Review Letters, Vol. 98, No. 2. (2007)</i><br /><br />Paramagnetic particles in a liquid above a solid dynamically self-assemble into two-dimensional (2D) viscoelastic clusters in a precessing magnetic field if the precession angle exceeds the magic angle. Hexagonal clusters rotate with a frequency proportional to the precession frequency of the magnetic field. The rotation is explained by viscoelastic shear waves excited in the clusters that can be visualized slightly above the magic angle. The cluster rotation and the visualization of viscoelastic modes are independent techniques to probe the rheological properties of the cluster. We find agreement between both techniques when determining the 2D cluster viscosity c10-11 N s/m. Viscoelasticity of Dynamically Self-Assembled Paramagnetic Colloidal Clusters Pietro Tierno Ramanathan Muruganathan Thomas Fischer doi:10.1103/PhysRevLett.98.028301 Physical Review Letters, Vol. 98, No. 2. (2007) 2008-03-19T17:16:50-00:00 2007 Physical Review Letters 98 2 APS 2007 cluster colloids magnetic