SHEAR-INDUCED PARTIAL TRANSLATIONAL ORDERING OF A COLLOIDAL SOLID
SHEAR-INDUCED PARTIAL TRANSLATIONAL ORDERING OF A COLLOIDAL SOLID
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DOI：
10.1103/physreva.30.906
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发表时间：
1984-01-01
影响因子：
2.9
通讯作者：
CLARK, NA
中科院分区：
文献类型：
--
作者：
ACKERSON, BJ;CLARK, NA
高电荷亚微米塑料球悬浮在水中，在低离子强度下，会自发排列成bcc晶体或多晶体。一个简单的线性剪切通过迫使（110）平面垂直于剪切梯度堆叠，并以与溶剂流动平行的< 111>方向相对滑动来定向和扰乱这些晶体。本文详细分析了bcc晶体在超出其固有弹性极限时发生的无序和流动过程。我们得到一个模型，在这个模型中，胶体晶体的流动被解释为与原子晶体中的流动有着根本不同的过程。在胶体晶体中，粒子运动与背景流体的耦合形成均匀流动，其中每一层相对于相邻层都处于运动状态。相反，原子固体中的塑性流动是缺陷介导的流动。在最低的外加应力下，胶体晶体中的局部bcc阶表现出平行和垂直于外加应力方向的剪切应变。假设胶体粒子之间有屏蔽的库仑对相互作用，利用bcc和畸变bcc晶体的构型能量来估计这些变形的大小。随着外加应力的增加，晶体的固有弹性极限被超过，晶体开始与相邻层流动，执行由粘性和屏蔽库仑力平衡控制的振荡路径。该路径从零剪切时观察到的bcc 1和bcc 2孪晶结构到中等剪切速率下扭曲的二维hcp结构，随着剪切的增加层间配准的损失。这一理论模型也与其他实验观察结果相一致。
Highly charged submicrometer plastic spheres suspended in water at low ionic strength will order spontaneously into bcc crystals or polycrystals. A simple linear shear orients and disorders these crystals by forcing (110) planes to stack normal to the shear gradient and to slide relative to each other with a< 111> direction parallel to the solvent flow. In this paper we analyze in detail the disordering and flow processes occurring beyond the intrinsic elastic limit of the bcc crystal. We are led to a model in which the flow of a colloidal crystal is interpreted as a fundamentally different process from that found in atomic crystals. In the colloidal crystal the coupling of particle motion to the background fluid forces a homogeneous flow, where every layer is in motion relative to its neighboring layers. In contrast, the plastic flow in an atomic solid is defect mediated flow. At the lowest applied stress, the local bcc order in the colloidal crystal exhibits shear strains both parallel and perpendicular to the direction of the applied stress. The magnitude of these deformations is estimated using the configurational energy for bcc and distorted bcc crystals, assuming a screened Coulomb pair interaction between colloidal particles. As the applied stress is increased, the intrinsic elastic limit of the crystal is exceeded and the crystal begins to flow with adjacent layers executing an oscillatory path governed by the balance of viscous and screened Coulomb forces. The path takes the structure from the bcc 1 and bcc 2 twins observed at zero shear to a distorted two-dimensional hcp structure at moderate shear rates, with a loss of interlayer registration as the shear is increased. This theoretical model is consistent with other experimental observations, as well.