Molecular Simulation on Fluid-to-Solid Phase Transition of Pressure-Activated Sealants
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摘要: 压差激活密封剂是一种含有复合液滴的多分散相流体。复合液滴水化膜在漏点压差作用下变形破碎，其内核在界面活性基团的吸附作用下聚集生长，最终充填微泄漏孔隙，完成密封损伤的原位修复。前期研究探索了复合液滴结构与压差激活的构效关系，为进一步揭示活性内核的聚结衍化规律，基于水化橡胶粒子的结构参数，构建了分散相内核聚集态分子模型，并采用量子化学与分子动力学相结合的方法，分析了聚集态单体与重复片段的静电势、Fukui函数与前线轨道、聚集态空间构型的回转半径与径向分布函数，研究了分散相聚结生长的动力学过程。结果显示：①分子片段中富电子羧基O、氰基N与缺电子共轭碳链共同组成了高分子聚集态的活性位点，其中羧基O与氰基N原子展示了最强局域亲核能力，而共轭碳链则具有最强局域亲电能力；②高分子聚集态具有核-壳空间构型，羧基O、氰基N作为壳层围绕内核展现层级分布，且聚集态亲电与亲核区域呈“锁-钥”构造，有利于分散相的空间识别与稳定缔合；③分散相生长经历了外层分子链收敛、体积塌缩、初始接触与内层分子链扩散4个阶段。研究结果从原子与分子层面揭示了复合液滴分散相的聚结衍化行为，有利于进一步完善力学-化学耦合作用下密封材料的微缺陷自适应修复机理。Abstract: Pressure Activated Sealant(PAS) is a type of polydisperse-phase fluid composed of rubber microparticle composite droplets. The liquid membrane of these composite droplets in PAS undergoes deformation and fragmentation under the impact of pressure differentials, exposing the interface of the rubber particles. The active functional groups at the interface promote microscopic phase coalescence and growth through chemical bonding, ultimately filling micro-leakage pores in situ and completing the mechanically-chemical coupled sealing process. Previous research explored the mechanical deformation behavior of composite droplets under pressure-differential impacts. To further investigate the chemical behavior of coalescence derivation, this work integrates the microstructural parameters of rubber microparticle composite droplets with quantum chemistry and molecular dynamics methods. A molecular model of the aggregated core state within the dispersed phase was constructed, and the following analyses were conducted, including Electrostatic Potential (ESP), Fukui simplified functions and frontier molecular orbitals (FMO), and aggregated spatial configuration (the radius of gyration and radial distribution function). The results showed that: ①Electron-rich carboxyl oxygen (O) and cyano nitrogen (N) atoms, along with electron-deficient conjugated carbon chains, constituted the active sites of the polymeric aggregation, wherein carboxyl O and cyano N atoms exhibited strong nucleophilic capabilities, while conjugated carbon chains demonstrated the strongest electrophilic tendencies; ② The aggregation state displayed a core-shell configuration, with the active carboxyl O and cyano N atoms forming the shell layers surrounding the core, showing unique hierarchical distribution. The nucleophilic and electrophilic regions of the aggregation formed a interesting "lock-and-key" structure, which is conducive to spatial recognition and enhancing the stability of aggregated adsorption and association; ③ The coalescence and fusion of the dispersed phase cores underwent four stages: outer molecular chain convergence, molecular volume collapse, initial contact, and inner molecular chain diffusion, ultimately leading to spontaneous growth into larger aggregated molecules. These findings reveal the chemical driving forces of coalescence within the dispersed phase at the atomic and molecular levels, which can not only improve the dynamic-chemical coupling model of the pressure difference-induced solidification in multiphase dispersed fluid, but also provide methodological insights for exploring the structure-property relationship of functional additives from a "molecular engineering" perspective.
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