Baum Markus, Rieutord Francois, Juranyi Fanni, Rey Cyrielle, Rébiscoul Diane
CEA, ICSM - UMR 5257 CEA-CNRS-UM-ENSCM , 30207 Bagnols-sur-Cèze Cedex, France.
Univ. Grenoble Alpes, IRIG-MEM , F-38000 Grenoble , France.
Langmuir. 2019 Aug 20;35(33):10780-10794. doi: 10.1021/acs.langmuir.9b01434. Epub 2019 Aug 8.
In this study, we characterized the structure and the dynamics at a picosecond scale of water molecules in aqueous solutions with cations having various kosmotropic properties (XCl where X = Ba, Ca, and Mg) confined in highly ordered mesoporous silica (MCM-41 and grafted MCM-41) by Fourier transform infrared spectroscopy and quasi-elastic neutron scattering. We pinpointed the critical pore size and the electrolyte concentration at which the influence of the ion nature becomes the main factor affecting the water properties. These results suggest that whatever the ions kosmotropic properties, for pore sizes ϕ < 2.6 nm and [XCl] ≤ 1 M, the water dynamics is mainly slowed down by the size of the confinement. For pore sizes of 6.6 nm, the water dynamics depends on the concentration and kosmotropic properties of the ion more than on the confinement. The water properties within the interfacial layer were also assessed and related to the surface ion excesses obtained by sorption isotherms. We showed that, for pore sizes ϕ ≥ 2.6 nm, the surface ion excess at the pore surface is the main driver affecting the structural properties of water molecules and their dynamics within the interfacial layer.
在本研究中，我们通过傅里叶变换红外光谱和准弹性中子散射，对含有具有不同促水合性质的阳离子（XCl，其中X = Ba、Ca和Mg）的水溶液中水分子在皮秒尺度下的结构和动力学进行了表征，这些阳离子被限制在高度有序的介孔二氧化硅（MCM - 41和接枝的MCM - 41）中。我们确定了临界孔径和电解质浓度，此时离子性质的影响成为影响水性质的主要因素。这些结果表明，无论离子的促水合性质如何，对于孔径ϕ < 2.6 nm且[XCl]≤1 M的情况，水动力学主要因受限尺寸而减慢。对于孔径为6.6 nm的情况，水动力学更多地取决于离子的浓度和促水合性质，而非受限情况。还评估了界面层内的水性质，并将其与通过吸附等温线获得的表面离子过量相关联。我们表明，对于孔径ϕ≥2.6 nm的情况，孔表面的表面离子过量是影响水分子结构性质及其在界面层内动力学的主要驱动因素。
