A contact angle observed for a liquid–solid system is not necessarily a unique value, and a few contact angles need to be considered carefully in relation to liquid spreading, adhesion and phase separation. Understanding of the significance of different contact angles has improved in the last few years through direct measurements of interactive forces between droplets/bubbles and solids together with the simultaneous visualization of the changes in their shapes. A microelectronic balance system is employed to measure the force of spreading after either liquid droplet or gas bubble attachment to a substrate surface and the droplet/bubble–substrate adhesion forces after droplet/bubble compression, retraction and detachment. Equipped with a camera in flank and data-acquisition software, the instrument measures directly the forces, monitors droplet/bubble–surface separation with respect to distances over which the droplet/bubble stretches and collects optical images simultaneously. The images are used to analyze capillary pressure and surface tension forces based on the measured droplet/bubble dimensions, shapes of surfaces and values of contact angles. These measurements allow researchers to correlate the advancing, receding and most stable contact angles with liquid–solid interactive forces and analyze their scientific meaning. This review summarizes the very recent literature reports on measurements and interpretation of liquid droplet/gas bubble interactive forces and associated contact angles.

中文翻译：

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用微量天平研究液滴扩散和粘附：综述

液-固系统观察到的接触角不一定是唯一值，需要仔细考虑与液体扩散、粘附和相分离相关的一些接触角。在过去几年中，通过直接测量液滴/气泡和固体之间的相互作用力以及同时可视化它们的形状变化，对不同接触角的重要性的理解有所提高。采用微电子天平系统测量液滴或气泡附着到基板表面后的扩散力，以及液滴/气泡压缩、收缩和分离后的液滴/气泡-基板粘附力。该仪器配备侧面摄像头和数据采集软件，直接测量力，监测液滴/气泡表面分离相对于液滴/气泡拉伸和同时收集光学图像的距离。这些图像用于根据测得的液滴/气泡尺寸、表面形状和接触角值分析毛细管压力和表面张力。这些测量使研究人员能够将前进、后退和最稳定的接触角与液-固相互作用力相关联，并分析它们的科学意义。这篇综述总结了最近关于液滴/气泡相互作用力和相关接触角的测量和解释的文献报告。这些图像用于根据测得的液滴/气泡尺寸、表面形状和接触角值分析毛细管压力和表面张力。这些测量使研究人员能够将前进、后退和最稳定的接触角与液-固相互作用力相关联，并分析它们的科学意义。这篇综述总结了最近关于液滴/气泡相互作用力和相关接触角的测量和解释的文献报告。这些图像用于根据测得的液滴/气泡尺寸、表面形状和接触角值分析毛细管压力和表面张力。这些测量使研究人员能够将前进、后退和最稳定的接触角与液-固相互作用力相关联，并分析它们的科学意义。这篇综述总结了最近关于液滴/气泡相互作用力和相关接触角的测量和解释的文献报告。