Reda Hilal, Katsamba Panayiota, Chazirakis Anthony, Harmandaris Vagelis
Computation-based Science and Technology Research Center, The Cyprus Institute, Aglantzia, Nicosia, 2121, Cyprus.
Institute of Applied and Computational Mathematics, Foundation for Research and Technology - Hellas, Heraklion, GR-71110, Greece.
Macromol Rapid Commun. 2024 Dec;45(24):e2400612. doi: 10.1002/marc.202400612. Epub 2024 Sep 18.
Polymer nanocomposites have found ubiquitous use across diverse industries, attributable to their distinctive properties and enhanced mechanical performance compared to conventional materials. Elucidating the elastic-to-plastic transition in polymer nanocomposites under diverse mechanical loads is paramount for the bespoke design of materials with desired mechanical attributes. In the current work, the elastic-to-plastic transition is probed in model systems of polyethylene oxide (PEO) and silica, SiO, nanoparticles, through detailed atomistic molecular dynamics simulations. This comprehensive, multi-scale analysis unveils pivotal markers of the elastic-to-plastic transition, highlighting the quintessential role of microstructural and regional heterogeneities in density, strain, and stress fields, featuring the polymer-nanoparticle interphase region. At the atomic level, the behavior of polymer chains interacting with nanoparticle surfaces is traced, differentiating between free and adsorbed chains, and identifying the microscopic origins of the linear-to-plastic transition. The mechanical behavior of subregions are characterized within the PEO/SiO nanocomposites, focusing on the interphase and bulk-like polymer areas, probing stress heterogeneities and their decomposition into various force contributions. At the inception of plasticity, a disruption is discerned in isotropy of the polymeric density field, the emergence of low-density regions, and microscopic voids/cavities within the polymer matrix concomitant with a transition of adsorbed chains to free. The yield strain also emerges as an inflection point in the local versus global strain diagram, demarcating the elastic limit, and the plastic regime shows pronounced strain heterogeneities. The decomposition of the atomic Virial stress into bonded and non-bonded interactions indicates that the rigidity of the material is primarily governed by non-bonded interactions, significantly influenced by the volume fraction of the nanoparticle. These findings emphasize the importance of the microstructural and micromechanical environment at the polymer-nanoparticle interface on the linear-to-plastic transition, which is of great importance in the design of nanocomposite materials with advanced mechanical properties.
聚合物纳米复合材料因其独特的性能以及与传统材料相比增强的机械性能，已在各行各业得到广泛应用。阐明聚合物纳米复合材料在不同机械载荷下的弹塑性转变，对于定制具有所需机械属性的材料至关重要。在当前工作中，通过详细的原子分子动力学模拟，对聚环氧乙烷（PEO）和二氧化硅（SiO）纳米颗粒的模型系统中的弹塑性转变进行了探究。这种全面的多尺度分析揭示了弹塑性转变的关键标志，突出了微观结构和区域不均匀性在密度、应变和应力场中的重要作用，尤其强调了聚合物 - 纳米颗粒界面区域的作用。在原子层面，追踪了与纳米颗粒表面相互作用的聚合物链的行为，区分了自由链和吸附链，并确定了线性到塑性转变的微观起源。对PEO/SiO纳米复合材料内各子区域的力学行为进行了表征，重点关注界面和类本体聚合物区域，探究应力不均匀性及其分解为各种力的贡献。在塑性开始时，聚合物密度场的各向同性出现破坏，低密度区域出现，聚合物基质内出现微观孔隙/空洞，同时吸附链向自由链转变。屈服应变也表现为局部与全局应变图中的一个拐点，划定了弹性极限，塑性区域表现出明显的应变不均匀性。将原子维里应力分解为键合和非键合相互作用表明，材料的刚度主要由非键合相互作用控制，受纳米颗粒体积分数的显著影响。这些发现强调了聚合物 - 纳米颗粒界面处的微观结构和微观力学环境对线性到塑性转变的重要性，这在设计具有先进机械性能的纳米复合材料中具有重要意义。
