Department of Chemical Engineering, Industrial Chemistry and Materials Science, University of Pisa, via Diotisalvi 2, 56126 Pisa, Italy.
Langmuir. 2010 Jun 1;26(11):8474-82. doi: 10.1021/la904914h.
A series of experimental precipitated calcium carbonates (PCCs) coated with commercial stearic acid (stearin), with the coating amount of stearin added to the PCC particles ranging from 3 to 13.5 wt %, were prepared in aqueous medium and characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). FTIR and TGA results indicated that only calcium stearate is present without any free stearic acid left on the surface of the produced PCCs. It was also found that the calcium stearate formed on the coated surface is partially chemisorbed and partially physisorbed. Interestingly, the surface coverage of the chemisorbed stearate, determined by the DSC technique in about 3.25 wt %, was much lower than the theoretical full monolayer coverage (4.17 wt %) for the same set of particles. This result was confirmed by determining the amount necessary to cover the filler with a full monolayer of surfactant by means of a dissolution method where the amount of dissolved surface agent, after the coating reaction, was measured by gas chromatography (GC). In other words, a complete chemisorbed monolayer on the surface cannot be reached, even in the presence of an amount of stearate ions far in excess compared to those required by the stoichiometry. This can be explained by considering that the coating in aqueous medium is quite different from solvent or dry coating, since the process is controlled by micelle adsorption, followed by the collapse of micelles into double or multiple layers during the drying stage.
一系列实验沉淀碳酸钙（PCC）用商业硬脂酸（硬脂）涂覆，硬脂酸的添加量范围为 PCC 颗粒的 3 至 13.5wt%，在水介质中制备并通过傅里叶变换红外光谱（FTIR）、热重分析（TGA）和差示扫描量热法（DSC）进行了表征。FTIR 和 TGA 结果表明，只有硬脂酸钙存在，而在生产的 PCC 表面上没有游离硬脂酸残留。还发现，在涂覆表面上形成的硬脂酸钙部分化学吸附和部分物理吸附。有趣的是，通过 DSC 技术确定的化学吸附硬脂酸的表面覆盖率（约 3.25wt%）远低于同一组颗粒的理论单层覆盖率（4.17wt%）。这一结果通过溶解法来确定用表面活性剂的单层完全覆盖填充剂所需的量来确认，其中在涂覆反应后，通过气相色谱（GC）测量溶解的表面活性剂的量。换句话说，即使存在远远超过化学计量所需的硬脂酸离子量，也无法达到表面的完全化学吸附单层。这可以通过考虑到在水介质中的涂层与溶剂或干涂层非常不同来解释，因为该过程由胶束吸附控制，随后在干燥阶段胶束坍塌成双层或多层。
