Zhou Yang, Hou Dongshuai, Geng Guoqing, Feng Pan, Yu Jiao, Jiang Jinyang
Jiangsu Key Laboratory of Construction Materials, School of Materials Science and Engineering, Southeast University, Nanjing 211189, China and Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, USA and State Key Laboratory of High Performance Civil Engineering Materials, Jiangsu Research Institute of Building Science Co., Nanjing 211103, China.
Department of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China.
Phys Chem Chem Phys. 2018 Mar 28;20(12):8247-8266. doi: 10.1039/c8cp00328a. Epub 2018 Mar 12.
The mechanical properties of organic/inorganic composites can be highly dependent on the interfacial interactions. In this work, with organic polymers intercalated into the interlayer of inorganic calcium silicate hydrate (C-S-H), the primary binding phase of Portland cement, great ductility improvement is obtained for the nanocomposites. Employing reactive molecular dynamics, the simulation results indicate that strong interfacial interactions between the polymers and the substrate contribute greatly to strengthening the materials, when C-S-H/poly ethylene glycol (PEG), C-S-H/poly acrylic acid (PAA), and C-S-H/poly vinyl alcohol (PVA) were subject to uniaxial tension along different lattice directions. In the x and z direction tensile processes, the Si-OCa bonds of the C-S-H gel, which were elongated and broken to form Si-OH and Ca-OH, play a critical role in loading resistance, while the incorporation of polymers bridged the neighboring silicate sheets, and activated more the hydrolytic reactions at the interfaces to avoid strain localization, thus increasing the tensile strength and postponing the fracture. On the other hand, Si-O-Si bonds of C-S-H mainly take the load when tension was applied along the y direction. During the post-yield stage, rearrangements of silicate tetrahedra occurred to prevent rapid damage. The polymer intercalation further elongates this post-yield period by forming interfacial Si-O-C bonds, which promote rearrangements and improve the connectivity of the defective silicate morphology, significantly improving the ductility. Among the polymers, PEG exhibits the strongest interaction with C-S-H, and thus C-S-H/PEG possesses the highest ductility. We expect that the molecular-scale mechanisms interpreted here will shed new light on the stress-activated chemical interactions at the organic/inorganic interfaces, and help eliminate the brittleness of cement-based materials on a genetic level.
有机/无机复合材料的力学性能可能高度依赖于界面相互作用。在本研究中，通过将有机聚合物插入无机水化硅酸钙（C-S-H）（波特兰水泥的主要粘结相）的层间，纳米复合材料的延展性得到了极大提高。采用反应分子动力学方法，模拟结果表明，当C-S-H/聚乙二醇（PEG）、C-S-H/聚丙烯酸（PAA）和C-S-H/聚乙烯醇（PVA）沿不同晶格方向承受单轴拉伸时，聚合物与基体之间的强界面相互作用对材料强化有很大贡献。在x和z方向的拉伸过程中，C-S-H凝胶的Si-OCa键被拉长并断裂形成Si-OH和Ca-OH，在承载过程中起关键作用，而聚合物的掺入桥接了相邻的硅酸盐片层，并更多地激活了界面处的水解反应以避免应变局部化，从而提高了拉伸强度并延缓了断裂。另一方面，当沿y方向施加拉力时，C-S-H的Si-O-Si键主要承受载荷。在屈服后阶段，硅酸盐四面体发生重排以防止快速破坏。聚合物插层通过形成界面Si-O-C键进一步延长了该屈服后阶段，促进了重排并改善了有缺陷的硅酸盐形态的连通性，显著提高了延展性。在这些聚合物中，PEG与C-S-H的相互作用最强，因此C-S-H/PEG具有最高的延展性。我们期望这里解释的分子尺度机制将为有机/无机界面处的应力激活化学相互作用提供新的见解，并有助于在基因水平上消除水泥基材料的脆性。
