Hipp Julie B, Ramos Paolo Z, Liu Qingsong, Wagner Norman J, Richards Jeffrey J
Center for Neutron Science, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716.
Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208.
Proc Natl Acad Sci U S A. 2024 Aug 20;121(34):e2403000121. doi: 10.1073/pnas.2403000121. Epub 2024 Aug 13.
Electron transport in complex fluids, biology, and soft matter is a valuable characteristic in processes ranging from redox reactions to electrochemical energy storage. These processes often employ conductor-insulator composites in which electron transport properties are fundamentally linked to the microstructure and dynamics of the conductive phase. While microstructure and dynamics are well recognized as key determinants of the electrical properties, a unified description of their effect has yet to be determined, especially under flowing conditions. In this work, the conductivity and shear viscosity are measured for conductive colloidal suspensions to build a unified description by exploiting both recent quantification of the effect of flow-induced dynamics on electron transport and well-established relationships between electrical properties, microstructure, and flow. These model suspensions consist of conductive carbon black (CB) particles dispersed in fluids of varying viscosities and dielectric constants. In a stable, well-characterized shear rate regime where all suspensions undergo self-similar agglomerate breakup, competing relationships between conductivity and shear rate were observed. To account for the role of variable agglomerate size, equivalent microstructural states were identified using a dimensionless fluid Mason number, [Formula: see text], which allowed for isolation of the role of dynamics on the flow-induced electron transport rate. At equivalent microstructural states, shear-enhanced particle-particle collisions are found to dominate the electron transport rate. This work rationalizes seemingly contradictory experimental observations in literature concerning the shear-dependent electrical properties of CB suspensions and can be extended to other flowing composite systems.
复杂流体、生物体系和软物质中的电子输运是从氧化还原反应到电化学能量存储等一系列过程中的一个重要特性。这些过程通常采用导体 - 绝缘体复合材料，其中电子输运性质从根本上与导电相的微观结构和动力学相关联。虽然微观结构和动力学被公认为是电性能的关键决定因素，但尚未确定它们影响的统一描述，特别是在流动条件下。在这项工作中，通过利用最近对流动诱导动力学对电子输运影响的量化以及电性能、微观结构和流动之间已确立的关系，对导电胶体悬浮液的电导率和剪切粘度进行了测量，以建立统一描述。这些模型悬浮液由分散在不同粘度和介电常数流体中的导电炭黑（CB）颗粒组成。在所有悬浮液都经历自相似团聚体破裂的稳定、特征明确的剪切速率范围内，观察到了电导率和剪切速率之间的竞争关系。为了考虑团聚体尺寸变化的作用，使用无量纲流体梅森数[公式：见原文]确定了等效微观结构状态，这使得能够分离动力学对流动诱导电子输运速率的作用。在等效微观结构状态下，发现剪切增强的颗粒 - 颗粒碰撞主导了电子输运速率。这项工作解释了文献中关于CB悬浮液剪切依赖电性能的看似矛盾的实验观察结果，并且可以扩展到其他流动复合体系。
