Whereas classical surface chemistry holds that capillarity controls fluid behavior, recent investigations indicate that it also dominates the mechanics of soft solids at scales below the elastocapillary length (l_e), which is the ratio of surface tension γ of liquid to elastic modulus E of the solid. We used atomic force microscopy to probe elastocapillary deformations induced by droplets of various radii (R) on partially wetting rubbery films of entangled polymers possessing thicknesses down to 230 nm. The transition from elasticity to capillarity dominated deformation with decreasing R values is visualized with high spatial resolution. The elasticity-to-capillarity transition shifted to lower R values, when the film thickness (h) is reduced to a threshold below approximately 10 times of the bulk l_e (l_e,bulk) values, indicative of a smaller l_e on the thin films. This enabled the identification of a thickness-dependent elastocapillary length (l_e,h) ∼ (h³γ/E)^1/4 for soft polymer films on rigid substrates, and, by extension, suggests the scaling l_e,h ∼ h^–n, where n varies with the contrast between the moduli of the films and substrates. The results resolve the foundation of the fluid wetting and interactions with thin, substrate-supported soft films.

中文翻译：

---

受支撑的橡胶状聚合物薄膜的润湿诱导弹性毛细管变形


虽然经典表面化学认为毛细作用控制流体行为，但最近的研究表明，在低于弹性毛细管长度 （l e） 的尺度上，毛细管作用也主导着软固体的力学，弹性毛细管长度 （l_e） 是液体表面张力 γ 与固体弹性模量 E 的比率。我们使用原子力显微镜探测各种半径 （R） 的液滴在厚度低至 230 nm 的缠结聚合物的部分润湿橡胶膜上诱导的弹性毛细管变形。随着 R 值减小，从弹性到毛细作用为主的变形的转变以高空间分辨率可视化。当薄膜厚度 （h） 降低到低于体积 l_e （l_e，bulk） 值的大约 10 倍的阈值时，弹性到毛细管的转变转变为较低的 R 值，这表明薄膜上的 l_e 较小。这使得能够识别刚性基材上软聚合物薄膜的厚度依赖性弹性毛细管长度 （l _e，h） ∼ （h³γ/E）^1/4，并引申出标度 l _e，h∼ h^–n，其中 n随薄膜和基材模量之间的对比度而变化。结果解决了流体润湿的基础以及与基材支撑的薄软膜的相互作用。