Cheng Luqing, Zhou Yang, Zhang Hao, Xiao Shuai, Li Weihuan, Chen Wentao
School of Materials Science and Engineering, Southeast University, Nanjing, Jiangsu 211189, China.
State Key Laboratory of High Performance Civil Engineering Materials, Jiangsu Research Institute of Building Science Co., Nanjing 211103, China.
Phys Chem Chem Phys. 2024 Mar 20;26(12):9399-9412. doi: 10.1039/d3cp05000a.
In recent years, polymers have been demonstrated to effectively toughen cementitious materials. However, the mechanism of interaction between the polymers and C-S-H at the nanoscale remains unclear, and the quantitative impact of the polymer chain length on toughening effectiveness is lacking in research. This study employs molecular dynamics techniques to examine the impact of the polyvinyl alcohol (PVA) chain length on the tensile performance and toughening mechanism of C-S-H. The toughening effect in both the and directions exhibits an initial enhancement followed by a decline with increasing chain length. The optimal degrees of polymerization are determined to be 8 and 12 in the and directions, respectively, resulting in an improvement of fracture energy by 146.7% and 29.5%, respectively. During the stretching process along the and axes, the chain length of PVA molecules significantly influences the variation in the number of Ca⋯O bonds in the system, leading to different stress responses. Additionally, PVA molecules form C-O-Si bonds with the silicate layers of C-S-H, bridging the adjacent layers in a left-right or up-down manner. The toughening effect of PVA on C-S-H depends on the behavior of PVA molecules with different chain lengths, and there exists an optimal range of chain length for PVA, enabling it to enhance structural uniformity and adjust its own conformation to absorb strain energy. When the length of PVA molecular chains is too short, it can easily cause stress concentration in the system and its connection with silicates is not significant. Conversely, when the length of PVA molecular chains is too long, the large molecular structure restricts its extension in the defects of C-S-H, and as the stretching progresses, PVA molecules break and form numerous small segments, thereby losing the advantage of the chain length. This study provides a theoretical basis for the ability of polymers to toughen cementitious materials.
近年来，已证明聚合物能有效增韧水泥基材料。然而，聚合物与纳米尺度的C-S-H之间的相互作用机制仍不明确，且聚合物链长对增韧效果的定量影响缺乏研究。本研究采用分子动力学技术来研究聚乙烯醇（PVA）链长对C-S-H拉伸性能和增韧机制的影响。在 和 方向上的增韧效果均呈现出随链长增加先增强后下降的趋势。确定在 和 方向上的最佳聚合度分别为8和12，这分别使断裂能提高了146.7%和29.5%。在沿 和 轴的拉伸过程中，PVA分子链长显著影响体系中Ca⋯O键数量的变化，导致不同的应力响应。此外，PVA分子与C-S-H的硅酸盐层形成C-O-Si键，以左右或上下方式连接相邻层。PVA对C-S-H的增韧效果取决于不同链长的PVA分子的行为，且PVA存在一个最佳链长范围，使其能够增强结构均匀性并调整自身构象以吸收应变能。当PVA分子链长度过短时，容易在体系中引起应力集中，且其与硅酸盐的连接不显著。相反，当PVA分子链长度过长时，大分子结构会限制其在C-S-H缺陷中的伸展，随着拉伸进行，PVA分子断裂并形成许多小片段，从而失去链长优势。本研究为聚合物增韧水泥基材料的能力提供了理论依据。
