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.
Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, 3584 CC, Utrecht, The Netherlands.
Proc Natl Acad Sci U S A. 2014 Oct 28;111(43):15356-61. doi: 10.1073/pnas.1411215111. Epub 2014 Oct 15.
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.
晶体中的应力松弛是通过缺陷的形成和扩散来介导的。尽管已经很好地确定了外部产生的应力如何通过晶格中位错的增殖和运动来松弛，但晶体如何应对内部应力仍然相对未知。我们通过实验和模拟研究了 2D 软胶体晶体中高度局域化的应力如何松弛。当单个粒子通过光镊被主动激发时，会产生多种高度集体的应力松弛机制。这些松弛过程表现为通过分离的空位-间隙对的协同运动和移动粒子的闭合环来协同移动的开放字符串，这要么是由于瞬时生成的圆形晶界中的协同旋转产生的，要么是通过空位-间隙对的湮灭来闭合开放字符串产生的。令人惊讶的是，我们发现仅由热波动激发的晶体中也会发生相同的集体事件；晶格内部的大热骚动会引发数百个粒子的不可逆位移。我们的结果说明了局部应力如何在 2D 软胶体晶体中诱导大规模的协同动力学，并揭示了超软晶体中的稳定机制。
