Kim Hojin, Esser-Kahn Aaron P, Rowan Stuart J, Jaeger Heinrich M
Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637.
James Franck Institute and Department of Physics, University of Chicago, Chicago, IL 60637.
Proc Natl Acad Sci U S A. 2023 Dec 5;120(49):e2310088120. doi: 10.1073/pnas.2310088120. Epub 2023 Nov 28.
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.
浓缩悬浮液的一个标志是非牛顿行为，即一旦超过特征剪切速率或应力，粘度就会急剧增加。这种强烈的剪切增稠被认为源于摩擦颗粒间接触力网络，该网络在足够大的应力下形成，动态演化，并适应变化的载荷。虽然有很多来自模拟的证据表明在剪切增稠过程中会出现这种网络，但实验证实一直很困难。在这里，我们使用压电纳米颗粒悬浮液，并利用网络内强烈的局部应力聚焦来激活电荷产生。然后可以在测量的交流电导率中检测到这种充电，并将其作为摩擦接触形成的标志。通过跟踪振荡剪切下接触网络中结构记忆的出现，以及展示应力激活摩擦如何驱动具有非线性反应动力学的化学反应的机械转导，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。综上所述，这使得压电悬浮液的交流电导率成为与摩擦相互作用相关的微观力学的灵敏原位报告器。
