Kirschner Johannes, Gomes Anderson H A, Marinho Ricardo R T, Björneholm Olle, Ågren Hans, Carravetta Vincenzo, Ottosson Niklas, Brito Arnaldo Naves de, Bakker Huib J
Ultrafast Spectroscopy, AMOLF, 1098 XG Science Park, Amsterdam, The Netherlands.
Phys Chem Chem Phys. 2021 May 21;23(19):11568-11578. doi: 10.1039/d0cp06387h. Epub 2021 May 11.
Mixtures of water and alcohol exhibit an excess surface concentration of alcohol as a result of the amphiphilic nature of the alcohol molecule, which has important consequences for the physico-chemical properties of water-alcohol mixtures. Here we use a combination of intensity vibrational sum-frequency generation (VSFG) spectroscopy, heterodyne-detected VSFG (HD-VSFG), and core-level photoelectron spectroscopy (PES) to investigate the molecular properties of water-ethanol mixtures at the air-liquid interface. We find that increasing the ethanol concentration up to a molar fraction (MF) of 0.1 leads to a steep increase of the surface density of the ethanol molecules, and an increased ordering of the ethanol molecules at the surface. When the ethanol concentration is further increased, the surface density of ethanol remains more or less constant, while the orientation of the ethanol molecules becomes increasingly disordered. The used techniques of PES and VSFG provide complementary information on the density and orientation of ethanol molecules at the surface of water, thus providing new information on the molecular-scale properties of the surface of water-alcohol mixtures over a wide range of compositions. This information is invaluable in understanding the chemical and physical properties of water-alcohol mixtures.
由于酒精分子的两亲性，水和酒精的混合物表现出酒精的过量表面浓度，这对水 - 酒精混合物的物理化学性质具有重要影响。在这里，我们结合使用强度振动和频产生（VSFG）光谱、外差检测VSFG（HD - VSFG）和芯能级光电子能谱（PES）来研究水 - 乙醇混合物在气 - 液界面的分子性质。我们发现，将乙醇浓度增加到摩尔分数（MF）为0.1会导致乙醇分子表面密度急剧增加，并且表面乙醇分子的有序性增强。当乙醇浓度进一步增加时，乙醇的表面密度或多或少保持恒定，而乙醇分子的取向变得越来越无序。所使用的PES和VSFG技术提供了关于水表面乙醇分子密度和取向的互补信息，从而在广泛的组成范围内提供了关于水 - 酒精混合物表面分子尺度性质的新信息。这些信息对于理解水 - 酒精混合物的化学和物理性质非常宝贵。
