Laube Jens, Salameh Samir, Kappl Michael, Mädler Lutz, Colombi Ciacchi Lucio
Max Planck Institute for Polymer Research , 55128 Mainz, Germany.
Langmuir. 2015 Oct 20;31(41):11288-95. doi: 10.1021/acs.langmuir.5b02989. Epub 2015 Oct 6.
Interparticle forces govern the mechanical behavior of granular matter and direct the hierarchical assembling of nanoparticles into supramolecular structures. Understanding how these forces change under different ambient conditions would directly benefit industrial-scale nanoparticle processing units such as filtering and fluidization. Here we rationalize and quantify the contributions of dispersion, capillary, and solvation forces between hydrophilic TiO2 nanoparticles with sub-10 nm diameter and show that the humidity dependence of the interparticle forces is governed by a delicate interplay between the structure of adsorbed water layers and the surface roughness. All-atom molecular dynamics modeling supported by force-spectroscopy experiments reveals an unexpected decrease in the contact forces at increasing humidity for nearly spherical particles, while the forces between rough particles are insensitive to strong humidity changes. Our results also frame the limits of applicability of discrete solvation and continuum capillary theories in a regime where interparticle forces are dominated by the molecular nature of surface adsorbates.
颗粒间作用力决定了颗粒物质的力学行为，并指导纳米颗粒分层组装成超分子结构。了解这些力在不同环境条件下如何变化，将直接惠及诸如过滤和流化等工业规模的纳米颗粒加工单元。在此，我们对直径小于10 nm的亲水性TiO₂纳米颗粒之间的色散力、毛细力和溶剂化力的贡献进行了合理化分析和量化，并表明颗粒间作用力对湿度的依赖性由吸附水层结构与表面粗糙度之间的微妙相互作用所决定。由力谱实验支持的全原子分子动力学模拟表明，对于近球形颗粒，接触力在湿度增加时意外下降，而粗糙颗粒之间的力对湿度的强烈变化不敏感。我们的结果还界定了离散溶剂化理论和连续毛细管理论在颗粒间作用力由表面吸附物的分子性质主导的 regime 中的适用范围。
