Colloidal gels, sparse particle networks with large voids, are fundamental model systems of disordered porous materials. Unlike dense amorphous solids, they exhibit significant volumetric deformation while expelling solvents when subjected to external compression. Despite their importance in both natural and industrial settings, the relationship between their network microstructure and compressive yielding behavior has remained elusive. To address this problem, we employ confocal microscopy and a specially designed sample cell to observe the gravity-induced collapsing of colloidal gels at a single-particle level. The experimental insight gained is complemented by simulation results for gravitational collapse and homogeneous uniaxial compression. We find that, during compression, the microstructure of gels is uniquely determined solely by the local volume fraction. This relationship remains independent of the deformation strain history but is subtly influenced by the preparation history of the initial state. In contrast, compressive stress evolves as a unique function of local volume fraction, unaffected by both preparation and strain history, as long as the interparticle interaction remains identical. Moreover, we unveil that local yielding occurs in highly strained, narrow network domains, while highly stressed particles form chainlike structures to support the external stress. These findings suggest that colloidal gels undergoing compressive plastic deformation mechanically self-organize into a unique history-independent state to satisfy mechanical balance in a quasistatic condition, providing crucial microscopic insights into the compressive yielding behavior of particle network materials.

中文翻译：

---

单轴压缩屈服过程中颗粒网络的机械自组织

胶体凝胶是具有大空隙的稀疏颗粒网络，是无序多孔材料的基本模型系统。与致密的​​无定形固体不同，它们在受到外部压缩时表现出显着的体积变形，同时排出溶剂。尽管它们在自然和工业环境中都很重要，但它们的网络微观结构和压缩屈服行为之间的关系仍然难以捉摸。为了解决这个问题，我们采用共焦显微镜和专门设计的样品池来观察单颗粒水平上重力引起的胶体凝胶的塌陷。重力塌陷和均匀单轴压缩的模拟结果补充了实验获得的见解。我们发现，在压缩过程中，凝胶的微观结构仅由局部体积分数决定。这种关系仍然独立于变形应变历史，但受到初始状态的准备历史的微妙影响。相比之下，只要颗粒间相互作用保持相同，压应力就会作为局部体积分数的独特函数而演变，不受制备和应变历史的影响。此外，我们发现局部屈服发生在高应变、狭窄的网络域中，而高应力颗粒形成链状结构以支撑外部应力。这些发现表明，经历压缩塑性变形的胶体凝胶会机械地自组织成一种独特的与历史无关的状态，以满足准静态条件下的机械平衡，为颗粒网络材料的压缩屈服行为提供了重要的微观见解。