Over the last half-century, direct measurements of surface forces have been instrumental in the exploration of a multitude of phenomena in liquid, soft, and biological matter. Measurements of van der Waals interactions, electrostatic interactions, hydrophobic interactions, structural forces, depletion forces, and many other effects have checked and challenged theoretical predictions and motivated new models and understanding. The gold-standard instrument for these measurements is the surface force balance (SFB), or surface forces apparatus, where interferometry is used to detect the interaction force and distance between two atomically smooth planes, with 0.1 nm resolution, over separations from about 1 µm down to contact. The measured interaction force vs. distance gives access to the free energy of interaction across the fluid film; a fundamental quantity whose general form and subtle features reveal the underlying molecular and surface interactions and their variation. Motivated by new challenges in emerging fields of research, such as energy storage, biomaterials, non-equilibrium and driven systems, innovations to the apparatus are now clearing the way for new discoveries. It is now possible to measure interaction forces (and free energies) with control of electric field, surface potential, surface chemistry; to measure time-dependent effects; and to determine structure in situ. Here, we provide an overview the operating principles and capabilities of the SFB with particular focus on the recent developments and future possibilities of this remarkable technique.

中文翻译：

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表面力平衡：直接测量流体和软物质的相互作用

在过去的半个世纪中，表面力的直接测量有助于探索液体、软物质和生物物质中的多种现象。范德华相互作用、静电相互作用、疏水相互作用、结构力、耗尽力和许多其他效应的测量已经检查和挑战了理论预测，并激发了新的模型和理解。这些测量的黄金标准仪器是表面力天平 (SFB) 或表面力装置，其中干涉测量法用于检测两个原子级光滑平面之间的相互作用力和距离，分辨率为 0.1 nm，间距约为 1 µm下来联系。测量到的相互作用力与距离的关系可以得出跨液膜相互作用的自由能；一个基本量，其一般形式和微妙特征揭示了潜在的分子和表面相互作用及其变化。在能源存储、生物材料、非平衡和驱动系统等新兴研究领域的新挑战的推动下，设备的创新正在为新发现扫清道路。现在可以通过控制电场、表面电势、表面化学来测量相互作用力（和自由能）；测量随时间变化的影响；并确定原位结构。在这里，我们概述了 SFB 的操作原理和功能，特别关注这项卓越技术的最新发展和未来的可能性。