8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P9.48Tue 611:23-14:00Cluster crystals under shearArash Nikoubashman, 1 Gerhard Kahl, 2 and Christos Likos 31 Vienna University of Technology, Institute of Theoretical Physics and CMS, WiednerHauptstraße 8-10 1040, Vienna, Austria2 Vienna University of Technology, Vienna, Austria3 University of Vienna, Vienna, AustriaThe behavior of ordered crystals under steady shear is an open problem that has attractedstrong interest of experimental, theoretical and simulation research both for atomic [1] andfor colloidal [2] systems. Based on appropriate simulation techniques that correctly accountfor hydrodynamics, we show that a distinct class of colloidal crystals, consisting of mutuallyoverlapping ultrasoft particles, has a novel and universal response to steady shear. In particular, wediscover the formation of a string phase, in which the original, three-dimensional crystalline orderis reduced to a two-dimensional one, by the formation of long strings along the flow direction,which order in a hexagonal lattice on the gradient-vorticity plane. Such self-organization isunknown for conventional materials, which rather respond to shear by formation of interplanezig-zag motions or sliding planes [3]. This phenomenon can be nicely explained, taken intoaccount the stabilizing forces of an equilibrium cluster crystal and the self-amplifying, destructiveeffect of the shear forces. We further find that the hexagonal array of strings melts at highshear rates and we determine the critical shear rate by means of theoretical estimates that areconfirmed by the simulations. Finally, we establish that the nucleation rates of a crystal out of ametastable uniform melt are enormously accelerated by the application of shear, a phenomenonoften observed in experimental systems, in which pre-shearing of the substance is employed as amechanism to circumnavigate glass formation.[1] C. J. Wu et al., Nat. Mater. , 8, 223 (2009).[2] Y. L. Wu et al., Proc. Natl. Acad. Sci. U. S. A. , 106, 10564 (2009).[3] J. Vermant and M. J. Solomon, J. Phys.: Condens. Matter, 17, R187 (2005).The corresponding article has been submitted to Phys. Rev. Lett. on April 20th 2011.48