title: Highly cooperative stress relaxation in two-dimensional soft colloidal crystals.
abstract: Stress relaxation in crystalline solids is mediated by the formation and diffusion of defects. Although it is well established how externally generated stresses relax, through the proliferation and motion of dislocations in the lattice, it remains relatively unknown how crystals cope with internal stresses. We investigate, both experimentally and in simulations, how highly localized stresses relax in 2D soft colloidal crystals. When a single particle is actively excited, by means of optical tweezing, a rich variety of highly collective stress relaxation mechanisms results. These relaxation processes manifest in the form of open strings of cooperatively moving particles through the motion of dissociated vacancy-interstitial pairs, and closed loops of mobile particles, which either result from cooperative rotations in transiently generated circular grain boundaries or through the closure of an open string by annihilation of a vacancy-interstitial pair. Surprisingly, we find that the same collective events occur in crystals that are excited by thermal fluctuations alone; a large thermal agitation inside the crystal lattice can trigger the irreversible displacements of hundreds of particles. Our results illustrate how local stresses can induce large-scale cooperative dynamics in 2D soft colloidal crystals and shed light on the stabilization mechanisms in ultrasoft crystals.
authors.affiliation: Laboratory of Physical Chemistry and Colloid Science, Wageningen University, 6703 HB, Wageningen, The Netherlands; and Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, 3584 CC, Utrecht, The Netherlands.
authors.forename: Berend
authors.initials: B
authors.lastname: van der Meer
authors.affiliation: Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, 3584 CC, Utrecht, The Netherlands.
authors.forename: Weikai
authors.initials: W
authors.lastname: Qi
authors.affiliation: Laboratory of Physical Chemistry and Colloid Science, Wageningen University, 6703 HB, Wageningen, The Netherlands; and.
authors.forename: Remco G
authors.initials: RG
authors.lastname: Fokkink
authors.affiliation: Laboratory of Physical Chemistry and Colloid Science, Wageningen University, 6703 HB, Wageningen, The Netherlands; and.
authors.forename: Jasper
authors.initials: J
authors.lastname: van der Gucht
authors.affiliation: Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, 3584 CC, Utrecht, The Netherlands.
authors.forename: Marjolein
authors.initials: M
authors.lastname: Dijkstra
authors.affiliation: Laboratory of Physical Chemistry and Colloid Science, Wageningen University, 6703 HB, Wageningen, The Netherlands; and joris.sprakel@wur.nl.
authors.forename: Joris
authors.initials: J
authors.lastname: Sprakel
keywords: collective dynamics; colloids; crystals; defects; stress relaxation