In this study, we investigate the anomalous diffusion of methylene diphenylmethane-4,4′-diisocyanate (MDI) into fumed silica filled poly(dimethylsiloxane) (PDMS) elastomer, which occurs in the industrial application of polyurethane vacuum casting. The absorbed MDI polymerizes with moisture to polyurea within the silicone medium, forming a sequential semi interpenetrating polymer network. This results in the formation of polyurea clusters near the exposed surface. Here we focus on the spatially resolved chemical characterization on the micrometer scale utilizing time-of-flight secondary ion mass spectrometry (ToF-SIMS), transmission electron microscopy (TEM), helium ion microscopy (HIM), atomic force microscopy (AFM), thermo-gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) as well as nuclear magnetic resonance spectroscopy (NMR). The concentration profile was determined experimentally using a customized method based on TGA. It was shown that the polyurea reaction of the MDI causes a time-dependency of both the surface concentration and the diffusion coefficient. Six analytical solutions to the diffusion equation obeying different time-dependent boundary conditions with different physical implications are proposed and used to model the measured concentration profiles. The parameterized models showed good predictive power for the measured absorption data and thus substantiated the conjectured molecular phenomena.

在这项研究中，我们研究了亚甲基二苯基甲烷-4,4'-二异氰酸酯 (MDI) 向气相二氧化硅填充的聚二甲基硅氧烷 (PDMS) 弹性体中的异常扩散，这种扩散发生在聚氨酯真空浇注的工业应用中。吸收的 MDI 与水分在有机硅介质中聚合成聚脲，形成连续的半互穿聚合物网络。这导致在暴露表面附近形成聚脲簇。在这里，我们专注于利用飞行时间二次离子质谱 (ToF-SIMS)、透射电子显微镜 (TEM)、氦离子显微镜 (HIM)、原子力显微镜 (AFM)、热重分析 (TGA)、X 射线光电子能谱 (XPS) 以及核磁共振光谱 (NMR)。使用基于 TGA 的定制方法通过实验确定浓度分布。结果表明，MDI 的聚脲反应导致表面浓度和扩散系数的时间依赖性。提出了遵守具有不同物理含义的不同时间相关边界条件的扩散方程的六个解析解，并用于模拟测量的浓度分布。参数化模型对测量的吸收数据显示出良好的预测能力，从而证实了推测的分子现象。提出了遵守具有不同物理含义的不同时间相关边界条件的扩散方程的六个解析解，并用于模拟测量的浓度分布。参数化模型对测量的吸收数据显示出良好的预测能力，从而证实了推测的分子现象。提出了遵守具有不同物理含义的不同时间相关边界条件的扩散方程的六个解析解，并用于模拟测量的浓度分布。参数化模型对测量的吸收数据显示出良好的预测能力，从而证实了推测的分子现象。