近日，美国芝加哥大学詹姆斯·弗兰克研究所和物理系的Heinrich M.Jaeger与普利兹克分子工程学院的Stuart J. Rowan等人合作并取得一项新进展。经过不懈努力，他们成功利用压电纳米颗粒实现剪切悬浮液中应激活化摩擦的探测
该研究团队采用压电纳米颗粒悬浮液，并利用网络内部强烈的局部应力聚焦来激活电荷生成。这种充电现象可以在测量的交流电导中得以检测，作为摩擦接触形成的明确标志。研究人员进一步证明了应力激活的摩擦颗粒相互作用与压电悬浮液响应之间的直接联系，方法是通过追踪在振荡剪切作用下接触网络中结构记忆的形成，以及通过非线性反应动力学来揭示应力激活的摩擦是如何驱动化学反应的力传导的。综合来看，这些发现使得压电悬浮体的交流电导，成为一个对与摩擦相互作用相关的微力学高度敏感的原位报告工具。
据悉，浓缩悬浮液展现出一种非牛顿行为，即当剪切速率或应力超过一定阈值时，其粘度会突然急剧增加。这种强烈的剪切增稠被认为源于摩擦颗粒-颗粒接触力的网络。这种网络在受到足够大的应力时会形成，随着应力的变化动态演变，并能适应不同的载荷情况。尽管在模拟剪切增稠过程时有大量证据表明这种网络的存在，但通过实验手段来直接证实它一直存在挑战。
附：英文原文
Title: Stress-activated friction in sheared suspensions probed with piezoelectric nanoparticles
Author: Kim, Hojin, Esser-Kahn, Aaron P., Rowan, Stuart J., Jaeger, Heinrich M.
Issue&Volume: 2023-11-28
Abstract: A hallmark of concentrated suspensions is non-Newtonian behavior, whereby the viscosity increases dramatically once a characteristic shear rate or stress is exceeded. Such strong shear thickening is thought to originate from a network of frictional particle–particle contact forces, which forms under sufficiently large stress, evolves dynamically, and adapts to changing loads. While there is much evidence from simulations for the emergence of this network during shear thickening, experimental confirmation has been difficult. Here, we use suspensions of piezoelectric nanoparticles and exploit the strong local stress focusing within the network to activate charge generation. This charging can then be detected in the measured ac conductance and serve as a signature of frictional contact formation. The direct link between stress-activated frictional particle interactions and piezoelectric suspension response is further demonstrated by tracking the emergence of structural memory in the contact network under oscillatory shear and by showing how stress-activated friction can drive mechano-transduction of chemical reactions with nonlinear reaction kinetics. Taken together, this makes the ac conductance of piezoelectric suspensions a sensitive in-situ reporter of the micromechanics associated with frictional interactions.
DOI: 10.1073/pnas.2310088120
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2310088120