Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands.
Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, Netherlands.
Phys Rev Lett. 2018 Dec 14;121(24):246102. doi: 10.1103/PhysRevLett.121.246102.
The curvature dependence of the surface tension is central to the nucleation of liquids, but remains difficult to access experimentally and predict theoretically. This curvature dependence arises from the curvature-dependent molecular structure, which, for small nuclei, can deviate significantly from that of the planar liquid interface. Simulations and density functional theory have been used to predict this curvature dependence, however with contradicting results. Here, we provide the first direct measurement of the curvature-dependent surface tension in nucleating colloidal liquids. We employ critical Casimir forces to finely adjust colloidal particle interactions and induce liquid nucleation, and image individual nuclei at the particle scale to measure their curvature-dependent surface tension directly from thermally excited surface distortions. Using continuum models, we elucidate the interplay between nucleus structure, particle pair potential, and surface tension. Our results reveal a 20% lower surface tension for nuclei of critical size compared to bulk liquids, leading to 3 orders of magnitude higher nucleation rates, thus highlighting the importance of surface tension curvature corrections for accurate prediction of nucleation rates.
表面张力的曲率依赖性是液体成核的核心问题，但在实验上仍然难以测量，理论上也难以预测。这种曲率依赖性源于曲率依赖性的分子结构，对于小核，其可以与平面液体界面的结构显著偏离。模拟和密度泛函理论已被用于预测这种曲率依赖性，但结果却相互矛盾。在这里，我们首次直接测量了成核胶体液体的曲率依赖性表面张力。我们利用临界 Casimir 力来精细调节胶体粒子相互作用并诱导液体成核，并在粒子尺度上对单个核成像，从而直接从热激发的表面变形来测量它们的曲率依赖性表面张力。通过连续体模型，我们阐明了核结构、粒子对势能和表面张力之间的相互作用。我们的结果表明，与体相液体相比，临界尺寸核的表面张力低 20%，这导致成核速率高出 3 个数量级，从而突出了表面张力曲率修正对于准确预测成核速率的重要性。
