Li Tianchi, Dufresne Eric R, Kröger Martin, Heyden Stefanie
Soft and Living Materials, Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland.
Polymer Physics, Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland.
Macromolecules. 2023 Feb 8;56(4):1303-1310. doi: 10.1021/acs.macromol.2c02576. eCollection 2023 Feb 28.
Fracture phenomena in soft materials span multiple length and time scales. This poses a major challenge in computational modeling and predictive materials design. To pass quantitatively from molecular to continuum scales, a precise representation of the material response at the molecular level is vital. Here, we derive the nonlinear elastic response and fracture characteristics of individual siloxane molecules using molecular dynamics (MD) studies. For short chains, we find deviations from classical scalings for both the effective stiffness and mean chain rupture times. A simple model of a nonuniform chain of Kuhn segments captures the observed effect and agrees well with MD data. We find that the dominating fracture mechanism depends on the applied force scale in a nonmonotonic fashion. This analysis suggests that common polydimethylsiloxane (PDMS) networks fail at cross-linking points. Our results can be readily lumped into coarse-grained models. Although focusing on PDMS as a model system, our study presents a general procedure to pass beyond the window of accessible rupture times in MD studies employing mean first passage time theory, which can be exploited for arbitrary molecular systems.
软材料中的断裂现象跨越多个长度和时间尺度。这在计算建模和预测性材料设计中构成了重大挑战。为了从分子尺度定量过渡到连续介质尺度，精确表示分子水平的材料响应至关重要。在此，我们通过分子动力学（MD）研究推导了单个硅氧烷分子的非线性弹性响应和断裂特性。对于短链，我们发现有效刚度和平均链断裂时间均偏离经典标度律。一个由库恩链段组成的非均匀链的简单模型捕捉到了观察到的效应，并且与MD数据吻合良好。我们发现主导的断裂机制以非单调方式取决于所施加的力的尺度。该分析表明，常见的聚二甲基硅氧烷（PDMS）网络在交联点处失效。我们的结果可以很容易地整合到粗粒化模型中。尽管我们将重点放在PDMS作为一个模型系统上，但我们的研究提出了一种通用方法，可超越使用平均首次通过时间理论的MD研究中可及的断裂时间窗口，该方法可用于任意分子系统。
