Spin-probe-enabled sensing of fluids in confined geometries and interfaces

当固体表面限制流体的分子时，新的动力学表面将以增强粘度、局部有序或集体运动⎯的形式出现，其实际影响包括从摩擦学、材料加工到膜物理等领域。限制也会影响化学反应中的离子传输和/或速率和平衡浓度，所有这些都使小体积流体的物理化学成为人们广泛关注的主题。然而，研究这些效应是出了名的困难，主要是因为缺乏所需的灵敏度和空间或时间分辨率的实验方法。这个问题在多相系统中尤其严重，在催化或生物科学中很常见，因为从宏观信号中提取典型的微小限制信号往往是不切实际的困难。在这里，我们建议探索一种新的途径，通过使用固体中的近表面点缺陷作为局部纳米探针来研究受限流体。我们确定了两个互补的研究前沿：第一个利用基于NV的新型磁共振波谱方法来研究可变限制条件和表面疏水性下的水扩散；这一努力的一部分是开发适用于重水的新型传感策略，我们将在该领域结合实验和路径积分分子动力学模拟。第二项研究将重点放在外部铁磁针尖诱导梯度的使用上，我们将利用这种梯度来非侵入性地探测分子扩散和成像承压水中表面诱导的有序。在这里，我们将重点转移到中尺度流体系统的研究，在那里顺磁缺陷的使用仍然几乎没有被探索。为此，我们介绍了各种实验方案，我们将这些方案与我们帮助开创的磁共振技术相结合，在受控条件下研究模型流体的纳米体积。在采取这一路线时，我们充分利用了磁共振技术的卓越多功能性，我们在这里利用这一技术在广泛的时间范围内同时提取受限环境中的流体结构和动力学。因此，这一提议的智力价值在于我们选择解决的科学问题的基本价值，我们致力于探索的创新测量策略，以及我们采取的综合方法-同时结合纳米制造、分子动力学建模和测量。

When a solid surface confines the molecules of a fluid, new dynamicsemerges e.g., in the form of enhanced viscosity, local order, or collective motion ⎯ whose practical impact encompasses areas ranging from tribology and materials processing to membrane physics. Confinement also affects ion transport and/or the rate andequilibrium concentration in a chemical reaction, all of which makes the physical chemistry of small fluid volumes the subject of broad interest. Studying these effects, however, is notoriously difficult, mainly due to the lack of experimental methods with the required sensitivity and spatial or time resolution. This problem is particularlyacute in heterogeneous systems, common in catalysis or the biological sciences, because extracting the typically minute signatures of confinement from the macroscopic signals is often impractically difficult. Here we propose to explore a new route toinvestigating confined fluids through the use of near-surface point defects in solids as local, nanoscopic probes. We identify two complementary research fronts: The first one capitalizes on novel NV based magnetic resonance spectroscopy methods to investigatewater diffusion under variable confinement and surface hydrophobicity; also part of this effort is the development of novel sensing strategies adapted to heavy water, an area where we will combine experiments and path-integral molecular dynamics simulations. The second research thrust zeroes in on the use of external ferromagnetic-tip-induced gradients that we will leverage to non-invasively probe molecular diffusion and image surface-induced order in confined water. Here we shift the focus to the investigation ofmesoscale fluidic systems, where the use of paramagnetic defects remains virtually unexplored. To this end we introduce various experimental protocols, which we articulate with magnetic resonance techniques we helped pioneer to investigate nanoscopic volumes of model fluids under controlled conditions. In taking this route, wecapitalize on the superb versatility of magnetic resonance techniques, which we leverage here to simultaneously extract fluidic structure and dynamics in confined environments over a broad time scale. The intellectual merit of this proposal resides, therefore, in thefundamental value of the scientific problem we choose to tackle, the innovative measurement strategies we aim to explore, and the integrated approach we take — simultaneously combining nanofabrication, molecular dynamics modeling, and measurement.