We present a measurement cell that allows simultaneous measurement of second harmonic generation (SHG) and streaming potential (SP) at mineral-water interfaces with flat specimen that are suitable for non-linear optical (NLO) studies. The set-up directly yields SHG data for the interface of interest and can also be used to obtain information concerning the influence of flow on NLO signals from that interface. The streaming potential is at present measured against a reference substrate (PTFE). The properties of this inert reference can be independently determined for the same conditions. With the new cell, for the first time the SHG signal and the SP for flat surfaces have been simultaneously measured on the same surface. This can in turn be used to unambiguously relate the two observations for identical solution composition. The SHG test of the cell with a fluorite sample confirmed previously observed differences in NLO signal under flow vs. no flow conditions in sum frequency generation (SFG) investigations. As a second test surface, an inert (“hydrophobic”) OTS covered sapphire-c electrolyte interface was studied to verify the zeta-potential measurements with the new cell. For this system we obtained combined zeta-potential/SHG data in the vicinity of the point of zero charge, which were found to be proportional to each other as expected. Furthermore, on the accessible time scales of the SHG measurements no effects of flow, flow velocity and stopped flow occurred on the interfacial water structure. This insensitivity to flow for the inert surface was corroborated by concomitant molecular dynamics simulations. Finally, the set-up was used for simultaneous measurements of the two properties as a function of pH in automated titrations with an oxidic surface. Different polarization combinations obtained in two separate titrations, yielded clearly different SHG data, while under identical conditions zeta-potentials were exactly reproduced. The polarization combination that is characteristic for dipoles perpendicular to the surface scaled with the zeta-potentials over the pH-range studied, while the other did not. The work provides an advanced approach for investigating liquid/surface interactions which play a major role in our environment. The set-up can be upgraded for SFG studies, which will allow more detailed studies on the chemistry and the water structure at a given interface, but also the combined study of specific adsorption including kinetics in combination with electrokinetics. Such investigations are crucial for the basic understanding of many environmental processes from aquatic to atmospheric systems.

我们提供了一个测量单元，该单元可以同时测量适用于非线性光学（NLO）研究的带有扁平标本的矿泉水界面处的二次谐波生成（SHG）和流电势（SP）。该设置直接产生感兴趣接口的SHG数据，也可用于从该接口获取有关流量对NLO信号影响的信息。目前，相对于参考衬底（PTFE）测量了流动电势。对于相同条件，可以独立确定该惰性参考的属性。对于新电池，首次在同一表面上同时测量了SHG信号和用于平坦表面的SP。反过来，这可以用于将两个观察值明确地关联为相同的溶液成分。用萤石样品对电池进行的SHG测试证实了先前在总和频率生成（SFG）研究中在流动与无流动条件下观察到的NLO信号差异。作为第二测试表面，研究了惰性（“疏水性”）OTS覆盖的蓝宝石-c电解质界面，以验证新电池的ζ电位测量结果。对于该系统，我们在零电荷点附近获得了zeta势/ SHG组合数据，发现它们与预期的相互成比例。此外，在SHG测量的可访问时间尺度上，界面水结构上没有发生流量，流速和停止流量的影响。伴随的分子动力学模拟证实了这种对惰性表面流动的不敏感性。最后，该设置用于在具有氧化表面的自动滴定中同时测量两种性质随pH的变化。在两个单独的滴定中获得的不同极化组合产生了明显不同的SHG数据，而在相同条件下精确地再现了Zeta电位。在研究的pH范围内，垂直于表面的偶极子的极化组合具有zeta电位，而其他的则没有。这项工作为研究在我们的环境中起主要作用的液体/表面相互作用提供了一种先进的方法。可以升级设置以进行SFG研究，这将允许在给定的界面上对化学和水结构进行更详细的研究，而且还包括对特定吸附的综合研究，包括动力学与电动学的结合。这种调查对于从水到大气系统的许多环境过程的基本理解至关重要。