Zhou Tingtao, Brady John F
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125.
Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125.
Proc Natl Acad Sci U S A. 2024 Dec 10;121(50):e2407424121. doi: 10.1073/pnas.2407424121. Epub 2024 Dec 3.
Mechanical properties of disordered materials are governed by their underlying free energy landscape. In contrast to external fields, embedding a small fraction of active particles within a disordered material generates nonequilibrium internal fields, which can help to circumvent kinetic barriers and modulate the free energy landscape. In this work, we investigate through computer simulations how the activity of active particles alters the mechanical response of deeply annealed polydisperse colloidal gels. We show that the "swim force" generated by the embedded active particles is responsible for determining the mode of mechanical failure, i.e., brittle vs. ductile. We find, and theoretically justify, that at a critical swim force the mechanical properties of the gel decrease abruptly, signaling a change in the mode of mechanical failure. The weakening of the elastic modulus above the critical swim force results from the change in gel porosity and distribution of attractive forces among gel particles, while below the critical swim force, the ductility enhancement is caused by an increase of gel structural disorder. Above the critical swim force, the gel develops a pronounced heterogeneous structure characterized by multiple pore spaces, and the mechanical response is controlled by dynamical heterogeneities. We contrast these results with those of a simulated monodisperse gel that exhibits a nonmonotonic trend of ductility modulation with increasing swim force, revealing a complex interplay between the gel energy landscape and embedded activity.
无序材料的力学性能由其潜在的自由能景观决定。与外部场不同，在无序材料中嵌入一小部分活性粒子会产生非平衡内部场，这有助于规避动力学障碍并调节自由能景观。在这项工作中，我们通过计算机模拟研究活性粒子的活性如何改变深度退火的多分散胶体凝胶的力学响应。我们表明，嵌入的活性粒子产生的“游动力”决定了机械失效的模式，即脆性与韧性。我们发现并从理论上证明，在临界游动力下，凝胶的力学性能会突然下降，这表明机械失效模式发生了变化。临界游动力以上弹性模量的减弱是由于凝胶孔隙率和凝胶颗粒间吸引力分布的变化，而在临界游动力以下，延展性的增强是由凝胶结构无序度的增加引起的。在临界游动力以上，凝胶形成了以多个孔隙空间为特征的明显非均匀结构，并且力学响应由动力学非均匀性控制。我们将这些结果与模拟的单分散凝胶的结果进行对比，后者表现出随着游动力增加延展性调制的非单调趋势，揭示了凝胶能量景观与嵌入活性之间的复杂相互作用。
