Department of Physics, Institute for Soft Matter Synthesis and Metrology, Georgetown University, 37th and O Streets, N.W., Washington District Of Columbia 20057, USA.
CAPES Foundation, Ministry of Education of Brazil, Brasilia - DF 70.040-020, Brazil.
Nat Commun. 2017 Jun 21;8:15846. doi: 10.1038/ncomms15846.
Soft solids with tunable mechanical response are at the core of new material technologies, but a crucial limit for applications is their progressive aging over time, which dramatically affects their functionalities. The generally accepted paradigm is that such aging is gradual and its origin is in slower than exponential microscopic dynamics, akin to the ones in supercooled liquids or glasses. Nevertheless, time- and space-resolved measurements have provided contrasting evidence: dynamics faster than exponential, intermittency and abrupt structural changes. Here we use 3D computer simulations of a microscopic model to reveal that the timescales governing stress relaxation, respectively, through thermal fluctuations and elastic recovery are key for the aging dynamics. When thermal fluctuations are too weak, stress heterogeneities frozen-in upon solidification can still partially relax through elastically driven fluctuations. Such fluctuations are intermittent, because of strong correlations that persist over the timescale of experiments or simulations, leading to faster than exponential dynamics.
具有可调机械响应的软固体是新材料技术的核心，但应用的一个关键限制是它们随时间的渐进老化，这会显著影响它们的功能。普遍接受的观点是，这种老化是渐进的，其起源是比指数慢的微观动力学，类似于过冷液体或玻璃中的动力学。然而，时间和空间分辨测量提供了相反的证据：快于指数的动力学、间歇性和突然的结构变化。在这里，我们使用微观模型的 3D 计算机模拟来揭示控制通过热波动和弹性恢复分别进行应力松弛的时间尺度对于老化动力学至关重要。当热波动太弱时，凝固时冻结的应力各向异性仍可以通过弹性驱动的波动部分松弛。这种波动是间歇性的，因为在实验或模拟的时间尺度上仍然存在强烈的相关性，导致快于指数的动力学。
