Wilken Sam, Guerra Rodrigo E, Pine David J, Chaikin Paul M
Center for Soft Matter Research, Department of Physics, New York University, New York 10003, USA.
Phys Rev Lett. 2020 Oct 2;125(14):148001. doi: 10.1103/PhysRevLett.125.148001.
In periodically sheared suspensions there is a dynamical phase transition, characterized by a critical strain amplitude γ_{c}, between an absorbing state where particle trajectories are reversible and an active state where trajectories are chaotic and diffusive. Repulsive nonhydrodynamic interactions between "colliding" particles' surfaces have been proposed as a source of this broken time reversal symmetry. A simple toy model called random organization qualitatively reproduces the dynamical features of this transition. Random organization and other absorbing state models exhibit hyperuniformity, a strong suppression of density fluctuations on long length scales quantified by a structure factor S(q→0)∼q^{α} with α>0, at criticality. Here we show experimentally that the particles in periodically sheared suspensions organize into structures with anisotropic short-range order but isotropic, long-range hyperuniform order when oscillatory shear amplitudes approach γ_{c}.
在周期性剪切悬浮液中，存在一种动态相变，其特征为临界应变幅值γₑ，处于粒子轨迹可逆的吸收态与轨迹混沌且扩散的活跃态之间。“碰撞”粒子表面之间的排斥性非流体动力学相互作用被认为是这种时间反演对称性破缺的一个来源。一个名为随机组织的简单玩具模型定性地再现了这种转变的动力学特征。随机组织和其他吸收态模型表现出超均匀性，即在临界状态下，由结构因子S(q→0)∼qᵅ（α>0）量化的长长度尺度上密度涨落的强烈抑制。在这里，我们通过实验表明，当振荡剪切幅值接近γₑ时，周期性剪切悬浮液中的粒子会组织成具有各向异性短程有序但各向同性、长程超均匀有序的结构。
