Hou Dongshuai, Sun Mengqi, Wang Muhan, Chen Zheng, Wang Xinpeng, Zhang Yue, Wang Pan
Department of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China.
School of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China.
Phys Chem Chem Phys. 2023 Nov 15;25(44):30349-30360. doi: 10.1039/d3cp03266c.
Calcium ion, as an essential component in CASH, affects the aggregation and formation process of CASH, thereby influencing its microstructure and mechanical properties. However, the mechanism by which calcium ions affect the polymerization process of CASH is not yet fully understood. In this study, the effects of calcium ions on the polymerization process, coagulation state, and microstructure of CASH are investigated molecular dynamics simulation. The results indicate that the presence of a trace amount of Ca attracts oligomers towards the calcium-rich region, thus speeding up the polymerization to some extent, but as the Ca content increases, more Ca binds to the oxygen atoms in silica-oxygen tetrahedra and aluminum-oxygen tetrahedra, forming tight ion pairs and occupying the hydroxyl binding sites required for the polycondensation reaction. This inhibits the continuous aggregation of CASH gel and slows down the rate of polymerization. Additionally, Ca attracts oxygen atoms from free water molecules and free OH, forming Ca(OH) dispersed in the spatial structure, which hinders the formation of larger clusters. As a result, the higher the Ca ion content in the system, the lower the overall polymerization degree of the CASH gel, resulting in a decrease in the conversion of the 1 dimer to 2 and 3 chain structures, a shorter average chain length, poorer overall connectivity, and a transition from large clusters in a better-aggregated state to dispersed small clusters. This study sheds light on the polymerization reaction mechanism of CASH gels.
钙离子作为CASH中的一种必需成分，会影响CASH的聚集和形成过程，从而影响其微观结构和力学性能。然而，钙离子影响CASH聚合过程的机制尚未完全清楚。在本研究中，通过分子动力学模拟研究了钙离子对CASH聚合过程、凝聚状态和微观结构的影响。结果表明，微量Ca的存在会将低聚物吸引到富钙区域，从而在一定程度上加速聚合，但随着Ca含量的增加，更多的Ca与硅氧四面体和铝氧四面体中的氧原子结合，形成紧密的离子对并占据缩聚反应所需的羟基结合位点。这抑制了CASH凝胶的持续聚集并减缓了聚合速率。此外，Ca会从自由水分子和游离OH中吸引氧原子，形成分散在空间结构中的Ca(OH)，这阻碍了更大聚集体的形成。结果，体系中Ca离子含量越高，CASH凝胶的整体聚合度越低，导致1聚体向2链和3链结构的转化率降低、平均链长缩短、整体连通性变差，以及从聚集状态较好的大聚集体转变为分散的小聚集体。本研究揭示了CASH凝胶的聚合反应机制。
